Prospective evidence for independent nitrogen and phosphorus limitation of grasshopper (Chorthippus curtipennis) growth in a tallgrass prairie - Rode, M.; Lemoine, N.P.; M.D. Smith (PLoS One, 2017)
Insect herbivores play a pivotal role in regulating plant production and community composition, and their role in terrestrial ecosystems is partly determined by their feeding behavior and performance among plants of differing nutritional quality. Historically, nitrogen (N) has been considered the primary limiting nutrient of herbivorous insects, but N is only one of many potential nutrients important to insect performance. Of these nutrients, phosphorus (P) is perhaps the most important because somatic growth depends upon P-rich ribosomal RNA. Yet relatively few studies have assessed the strength of P-limitation for terrestrial insects and even fewer have simultaneously manipulated both N and P to assess the relative strengths of N- and P-limitation. Here, we tested for potential N and P limitation, as well as N:P co-limitation, on Chorthippis curtipennis (Orthoptera, Acrididae), an abundant member of arthropod communities of central US prairies. Our results demonstrate weak evidence for both N and P limitation of C. curtipennis growth rates in laboratory feeding assays. Importantly, P-limitation was just as strong as N-limitation, but we found no evidence for NP co-limitation in our study. Furthermore, nutrient limitation was not apparent in field studies, suggesting that insect growth rates may be predominately controlled by other factors, including temperature and predation. Our results suggest that P should be jointly considered, along with N, as a primary determinant of herbivore feeding behavior under both current and future climate conditions.

Pushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years - Alan K. Knapp; M.L. Avolio; Beier, C.; Carroll, C.J.W.; Scott. L. Collins; Dukes, J.S.; Fraser, L.H.; Griffin-Nolan, R.J.; Hoover, D.L.; Jentsch, A.; Loik, M.E.; Phillips, R.P.; et al. (Global Change Biology, 2017)
Intensification of the global hydrological cycle, ranging from larger individual precipitation events to more extreme multiyear droughts, has the potential to cause widespread alterations in ecosystem structure and function. With evidence that the incidence of extreme precipitation years (defined statistically from historical precipitation records) is increasing, there is a clear need to identify ecosystems that are most vulnerable to these changes and understand why some ecosystems are more sensitive to extremes than others. To date, opportunistic studies of naturally occurring extreme precipitation years, combined with results from a relatively small number of experiments, have provided limited mechanistic understanding of differences in ecosystem sensitivity, suggesting that new approaches are needed. Coordinated distributed experiments (CDEs) arrayed across multiple ecosystem types and focused on water can enhance our understanding of differential ecosystem sensitivity to precipitation extremes, but there are many design challenges to overcome (e.g., cost, comparability, standardization). Here, we evaluate contemporary experimental approaches for manipulating precipitation under field conditions to inform the design of ‘Drought-Net’, a relatively low-cost CDE that simulates extreme precipitation years. A common method for imposing both dry and wet years is to alter each ambient precipitation event. We endorse this approach for imposing extreme precipitation years because it simultaneously alters other precipitation characteristics (i.e., event size) consistent with natural precipitation patterns. However, we do not advocate applying identical treatment levels at all sites – a common approach to standardization in CDEs. This is because precipitation variability varies >fivefold globally resulting in a wide range of ecosystem-specific thresholds for defining extreme precipitation years. For CDEs focused on precipitation extremes, treatments should be based on each site's past climatic characteristics. This approach, though not often used by ecologists, allows ecological responses to be directly compared across disparate ecosystems and climates, facilitating process-level understanding of ecosystem sensitivity to precipitation extremes.

Reconciling inconsistencies in precipitation– productivity relationships: implications for climate change - Alan K. Knapp; Ciais, P.; M.D. Smith (New Phytologist, 2017)
Precipitation (PPT) is a primary climatic determinant of plant growth and aboveground net primary production (ANPP) over much of the globe. Thus, PPT–ANPP relationships are important both ecologically and to land–atmosphere models that couple terrestrial vegetation to the global carbon cycle. Empirical PPT–ANPP relationships derived from long-term site-based data are almost always portrayed as linear, but recent evidence has accumulated that is inconsistent with an underlying linear relationship. We review, and then reconcile, these inconsistencies with a nonlinear model that incorporates observed asymmetries in PPT–ANPP relationships. Although data are currently lacking for parameterization, this new model highlights research needs that, when met, will improve our understanding of carbon cycle dynamics, as well as forecasts of ecosystem responses to climate change.

Recovery and relative influence of root, microbial, and structural properties of soil on physically sequestered carbon stocks in restored grassland - Scott, D.A.; S.G. Baer; John M. Blair (Soil Science Society of America Journal, 2017)
Managing soil to sequester C can help mitigate increasing CO2 in the atmosphere. To maximize this ecosystem service, more knowledge of factors influencing C sequestration is needed. The objectives of this study were to (i) quantify recovery of the roots, microbial biomass and composition, and soil structure across a chronosequence of grassland restorations and (ii) use a structural equation model to develop a data-based hypothesis on the relative influence of physical and biological soil properties on the soil C aggregate fraction diagnostic of sequestered C. Belowground plant biomass and tissue quality (C/N ratio), soil microbial biomass C, phospholipid fatty acid (PLFA) concentrations, soil structure, and soil C stocks in the bulk soil and each aggregate fraction were quantified from a cultivated field, prairies restored for 1 to 35-yr (n = 6), and a never-cultivated (native) prairie. Root biomass, microbial biomass C, arbuscular mycorrhizal fungi (AMF) PLFA biomass across the chronosequence increase to resemble native prairie following 35 yr of restoration. Many aspects of soil structure (i.e., bulk density, proportional mass of aggregate fractions, and aggregate mean weighted diameter) and the distribution C among soil fractions, including C in the micro-within-macro aggregate fraction (sequestered C), also became representative of native prairie within 35 yr of restoration. Total soil C stock and physically protected C increased at a similar rate (23 and 27 g C m-2 yr-1) respectively, across the chronosequence. After 35 yr of restoration, 50% of the total C pool was physically protected. The structural equation modeling developed by these data hypothesizes that microbial biomass C and AMF biomass (microbial composition) have the strongest causal influence on physically protected C. This model needs to be tested using independent sites to achieve greater inference.

Restoration and management for plant diversity enhances the rate of belowground ecosystem recovery - Klopf, Ryan P.; S.G. Baer; E.M. Bach; Six, Johan (Ecological Applications, 2017)
The positive relationship between plant diversity and ecosystem functioning has been criticized for its applicability at large scales and in less controlled environments that are relevant to land management. To inform this gap between ecological theory and application, we compared recovery rates of belowground properties using two chronosequences consisting of continuously cultivated and independently restored fields with contrasting diversity management strategies: grasslands restored with high plant richness and managed for diversity with frequent burning (n = 20) and grasslands restored with fewer species that were infrequently burned (n = 15). Restoration and management for plant diversity resulted in 250% higher plant richness. Greater recovery of roots and more predictable recovery of the active microbial biomass across the high diversity management strategy chronosequence corresponded with faster recovery of soil structure. The high diversity grasslands also had greater nutrient conservation indicated by lower available inorganic nitrogen. Thus, mesic grasslands restored with more species and managed for high plant diversity with frequent burning enhances the rate of belowground ecosystem recovery from long-term disturbance at a scale relevant to conservation practices on the landscape
Keywords: Aggregates; Biodiversity; carbon; Ecosystem function; nitrogen; phospholipid fatty acid; prairie; root; soil

Restored prairie response to reduction in ectophagous insects - Black, S.M. (Southern Illinois University, 2017)

The role of soil heterogeneity in the recruitment of new species and interactions with grasshoppers (Acrididae) and Katydids (Tettigoniidae) in restored prairie - T. Adams (Southern Illinois University, 2017)

Role of spatial and temporal vegetation heterogeneity from fire-grazing interactions to the assembly of tallgrass prairie spider communities - Gómez, Jesús Enrique (Department of Biology, 2017)
North American tallgrass prairie is a dynamic ecosystem that evolved with variable regimes of fire and grazing interactions (pyric herbivory), and variable mid-continental weather. Combined, these ecological factors create a shifting mosaic of plant communities that create heterogeneous and structurally complex habitats that move around across the landscape in time and space. The overarching goal of my dissertation was to study how bottom-up habitat templates created in response to fire-grazing interactions influence the community structure of spiders, key arthropod predators in grassland food-webs. Spiders are a ubiquitous and diverse group of terrestrial predators that partition their habitat at fine scales with species distributions and abundances that are sensitive to habitat structure. Primary hypotheses examined include: (H1) Spider density, species diversity, species evenness and functional richness of hunting strategies should increase as the spatial heterogeneity of habitat structure and overall habitat productivity increases, as predicted by the habitat complexity and heterogeneity hypothesis. (H2) Pyric herbivory indirectly determines spider community structure through is effect on vegetation structure and spatial heterogeneity, thereby promoting the formation of a mosaic of spider species assemblages that track changes in the distribution of key habitat resources. My research takes advantage of a long-term, watershed-level manipulations of fire frequency and bison grazing across a topographically variable landscape at Kansas State University’s Konza Prairie Biological Station, a tallgrass prairie research site near Manhattan KS. Spider communities were sampled for three years at 23 sites representative of multiple habitat types ranging from low-stature grass-dominated sites to grassland-gallery forest transition zones. In addition, a field experiment was performed to test the hypothesis that vegetation structure contributes directly to web-builder abundance and web-type richness of spiders in open grasslands. Here, the availability of structure for web placement was increased by adding dead woody stems along transects in three watersheds that differed in burn histories and existing habitat structure in the absence of grazing. Results were consistent with the three key hypotheses. Species diversity and the functional diversity of spiders increased as the spatial heterogeneity and overall structure of habitat increased in response to fire-grazing interactions. Vegetation heterogeneity influenced spider community responses most strongly in the summer. Structural complexity of vegetation influenced spider diversity, species evenness and richness of hunting strategies throughout the growing season, becoming most important by the end of the growing season. The transitional ecotone between grasslands and woodlands supported a hotspot for spider density, species diversity and richness of hunting strategies along vegetation gradients (H1), and among habitat types (H2). Increasing the availability of web-anchoring structures in open grasslands led to increased web-builder density in open grassland, particularly for small and medium sized orb-web species that took advantage of increased physical structure. Disturbance from pyric herbivory indirectly promoted dynamic and malleable assemblages of spider species that coexisted in syntopy through effects on vegetation structure and its availability in time and space. Changes in habitat structure and heterogeneity as spatially and temporally shifting mosaics of habitat type increased the overall spider diversity at the landscape scale.
Keywords: Fire and grazing interactions; habitat structure; Konza Prairie Biological Station; Spatial and temporal heterogeneity; Spider community

Small mammals in anthropogenic brome fields as compared to native tallgrass prairie in the northern flint hills of kansas - D.W. Kaufman; Kaufman, G.A. (Transactions of the Kansas Academy of Science, 2017)
We studied small mammals in planted smooth brome (Bromus inermis) fields on Konza Prairie to assess the small mammal community associated with these frequently occurring anthropogenic grasslands in eastern Kansas. Also, we wanted to understand the impacts of land use changes resulting from this type of anthropogenic change as compared to native habitats. Relative to this latter interest, we compared the small mammal community in brome fields to that found in native tallgrass prairie, also on Konza Prairie, for the same years and seasons during the early to mid-1980s. Small mammals were trapped in brome (n = 2 study sites) and native tallgrass prairie (n = 14) in autumn (6 years), spring (5) and summer (4) during 1981–1986. Overall, 173 and 1893 individuals of rodents and shrews were captured in brome and native prairie, respectively. Across all seasons, community abundance in brome was greater in autumn than in spring and summer. Patterns of community abundance among seasons in brome were not proportionally similar to those found in tallgrass prairie. Although proportions in autumn were similar, the patterns in spring and summer were in contrasting directions; spring was higher in brome and summer was higher in prairie. When all seasons were combined, no effect on community abundance was observed from burning the brome fields. Community abundance in brome was similar on burned and unburned traplines in autumn and spring but not in summer. In summer, greater abundance of small mammals occurred on burned than on unburned research sites. The proportion of small mammals in burned brome fields in the three seasons mirrored the proportions observed on burned sites in native prairie. In contrast, these proportions were not similar for spring and summer in brome and prairie for unburned study sites. Species composition and the numerical dominance of species varied greatly between brome fields and native prairie overall as well as among seasons. Prairie voles (Microtus ochrogaster) were numerically dominant in brome fields, whereas deer mice (Peromyscus maniculatus) were in native prairie. Furthermore, herbivorous rodents were numerically dominant in brome fields, whereas seed-eating omnivores were the predominant species in native prairie. Finally, our study indicates that agricultural land use change can result in temporally and spatially variable small mammal communities that do not mirror those found in native tallgrass prairie.
Keywords: community abundance; deer mouse; fire; prairie vole; relative abundance; rodents; shrews; Species composition; Species richness

Small vegetation gaps increase reseeded yellow-flowered alfalfa performance and production in native grasslands - Zhou, Jiqiong; Zhang, Yingjun; G.T. Wilson; Cobb, Adam B.; Lu, Wenjie; Guo, Yanping (Basic and Applied Ecology, 2017)
Reseeding yellow-flowered alfalfa (YFA) in degraded grasslands may require a vegetation-free microsite for germination and subsequent establishment. This study aimed to examine the role of microclimates of different-sized vegetation gaps on seedling performance and adult plant production of YFA. Field microsites were established in the meadow steppe of Hulunber, Inner Mongolia, China. Seedling performance, plant production, the microclimate within vegetation gaps, and soil nutrients (plant-available N, P, and K, total N concentration) were assessed at the end of each growing season from 2013 to 2015. Our results indicate light availability, and topsoil temperature of each gap were significantly increased as gap size increased, while topsoil moisture and air relative moisture were decreased in larger gaps. Small gaps (diameter ≤10 cm) improved seedling emergence, survival, biomass, and root nodulation, as compared with seedling performance associated with the larger gaps, presumably in response to increased shade and moisture. Additionally, large gaps (>20 or >40 cm) were characterized by significantly lower plant-available P, total N concentrations, plant-available K, and soil pH. However, root exclusion treatments did not improve overall seedling performance, plant production, or soil properties, as compared to corresponding microsites with root presence, regardless of gap size. Our results suggest that reseeding YFA into grasslands where disturbance, such as light grazing, has resulted in small gaps will be more effective than in highly degraded grasslands.

Space use of female greater Prairie-Chickens in response to fire and grazing interactions - Winder, Virginia L.; McNew, Lance B.; Pitman, Jim C.; Sandercock, B.K. (Rangeland Ecology & Management, 2017)
Ecological interactions between fire and grazing have shaped the evolutionary history of grassland ecosystems. Currently, grassland birds have experienced ongoing population declines, following widespread implementation of intensive rangeland management practices that reduce habitat heterogeneity. Patch-burn grazing is an alternative rangeland management strategy that promotes habitat heterogeneity and biodiversity. We conducted a 3-yr. field study in the central Flint Hills of Kansas to compare the spatial ecology of female Greater Prairie-Chickens (Tympanuchus cupido) in rangelands managed with intensive rangeland management versus patch-burn grazing. This is the first study on the effects of patch-burn grazing on the space use decisions of Greater Prairie-Chickens at the home range scale. We used seasonal estimates of home range for 6-mo breeding and nonbreeding periods, as well as resource utilization functions to investigate the response of female prairie chickens to landscape metrics describing fire, grazing, and proximity to anthropogenic structures or lek sites. In our analysis of all radio-marked females, distance to lek was consistently the strongest predictor of space use during both breeding and nonbreeding seasons. Females captured at properties managed with patch-burn grazing selected areas with low stocking rates and high fire frequencies, and they avoided recently burned areas. Our study provides new evidence that patch-burn grazing can improve grassland habitat for Greater Prairie-Chickens, an umbrella species in the tallgrass prairie ecosystem. Patch-burn grazing created preferred habitats for female Greater Prairie-Chickens, with a relatively frequent fire return interval, a mosaic of burned and unburned patches, and a reduced stocking rate in unburned areas avoided by grazers. Widespread implementation of patch-burn grazing could result in significant improvements in habitat quality for wildlife in the tallgrass prairie ecosystem.
Keywords: Home range; intensive early stocking; patch-burn grazing; prescribed fire; resource utilization function; Tympanuchus cupido

Species reordering, not changes in richness, drives long-term dynamics in grassland communities - Jones, Sydney K.; Ripplinger, Julie; Scott. L. Collins (Ecology Letters, 2017)
Determining how ecological communities will respond to global environmental change remains a challenging research problem. Recent meta-analyses concluded that most communities are undergoing compositional change despite no net change in local species richness. We explored how species richness and composition of co-occurring plant, grasshopper, breeding bird and small mammal communities in arid and mesic grasslands changed in response to increasing aridity and fire frequency. In the arid system, grassland and shrubland plant and breeding bird communities were undergoing directional change, whereas grasshopper and small mammal communities were stable. In the mesic system, all communities were undergoing directional change regardless of fire frequency. Despite directional change in composition in some communities, species richness of all communities did not change because compositional change resulted more from reordering of species abundances than turnover in species composition. Thus, species reordering, not changes in richness, explains long-term dynamics in these grass and shrub dominated communities.
Keywords: Community dynamics; desert grassland; desert shrubland; fire; species reordering; Species richness; tallgrass prairie

Temporal variability in large grazer space use in an experimental landscape - Raynor, E.J.; Anthony Joern; Skibbe, A.M.; Sowers, M.; J. M. Briggs; Laws, A.N.; Goodin, D.G. (Ecosphere, 2017)
Land use, climate change, and their interaction each have great potential to affect grazing systems. With anticipated more frequent and extensive future drought, a more complete understanding of the mechanisms that determine large grazer landscape-level distribution under varying climatic conditions is integral to ecosystem management. Using an experimental setting with contrasting fire treatments, we describe the inter-annual variability of the effect of landscape topography and disturbance from prescribed spring fire on large grazer space use in years of variable resource availability. Using GPS telemetry, we investigated space use of plains bison (Bison bison bison) as they moved among watersheds managed with variable experimental burn treatments (1-, 2-, 4-, and 20-year burn intervals) during a seven-year period spanning years of average-to-above average forage production and severe drought. At the landscape scale, bison more strongly favored high-elevation and recently burned watersheds with watersheds burned for the first time in 2 or 4 yr consistently showing higher use relative to annually burned watersheds. In particular, watersheds burned for the first time in 4 yr were avoided to lesser extent than other more frequently burned watersheds during the dormant season. This management type also maintained coupling between bison space use and post-fire regrowth across post-drought growing season months, whereas watersheds with more frequent fire-return intervals attracted bison in only the first month post-fire. Hence, fire frequency played a role in maintaining the coupling of grazer and post-fire regrowth, the fire–grazer interaction, in response to drought-induced reduction in fuel loads. Moreover, bison avoided upland habitat in poor forage production years, when forage regrowth is less likely to occur in upland than in lowland habitats. Such quantified responses of bison to landscape features can aid future conservation management efforts and planning to sustain fire–grazer interactions and resulting spatial heterogeneity in grassland ecosystems.

Testing metabolic cold adaptation as a driver of warm-water fish species replacement along the river continuum - Troia, Matthew J.; K. B. Gido (Environmental Biology of Fishes, 2017)
Hydrologic and thermal regimes vary along the upstream-to-downstream river continuum and drive the assembly of fish communities. The metabolic cold adaptation (MCA) hypothesis predicts that faster development is adaptive for species exposed to shorter growing seasons. Whether gradients of hydrologic variability and seasonal thermal regime associated with the river continuum operate as environmental filters on species with differing developmental rates remains an untested mechanism of community assembly. We analyzed daily records of stream discharge and modeled stream temperatures to quantify these two gradients of abiotic harshness in Kansas, USA. We then used laboratory experiments to compare temperature-dependent larval development rates among three congeneric cyprinid species that are most abundant in small tributaries (Pimephales promelas), medium tributaries (P. notatus), or river mainstems (P. vigilax). Growing season duration increased with stream size, with temperature exceedance thresholds of 22 and 26 °C lasting 1.4 and 270 times longer, respectively, in eighth order river mainstems compared to second order tributaries. The frequency of small flood pulses within the growing season peaked in mid-order streams, whereas the frequency of large flood pulses within the growing season peaked in low-order streams. Larval development rates increased with incubation temperature, but did not differ predictably among species. These findings, when viewed alongside a companion study, suggest that thermal adaptation and not MCA explains the replacements of Pimephales species along the river continuum. The prominent upstream-to-downstream gradient in growing season duration highlights the need for studies on the evolutionary and ecological significance of this infrequently explored characteristic of the river continuum.

Use of vegetation sampling and analysis to detect a problem within a portion of a prairie restoration project - Franson, Raymond; Scholes, Chad; Krabbe, Stephen (International Journal of Phytoremediation, 2017)
In June 2005, the Department of Energy (DOE) began establishing the 60-ha Howell Prairie around the disposal cell at the DOE Weldon Spring Site (WSS). Prairies were historically present in the area of the site. Quantitative Cover sampling was used to quantify Total Cover, Native Grass Cover, Non-Native Grass Cover, Native Forb Cover, Non-Native Forb Cover, Warm Season (C-4 Grass), Cool Season (C-3 Grass), Perennial Cover and Annual Cover, Litter, and Bare Ground. Four permanent vegetation sampling plots were established. The first 4 years of vegetation measurements at Howell Prairie were made during above-average rainfall years on burned and unburned plots. The fifth-year (2012) vegetation measurements were made after below-average rainfall. Five years of results not only document the consistency of the restoration effort in three areas, but also demonstrate deficiencies in Grass Cover in a fourth area. The results are not only useful for Howell Prairie, but will be useful for restoration work throughout the region. Restoration work suffers from a lack of success monitoring and in this case from a lack of available reference areas. Floristic Quality Indices are used to make qualitative comparisons of the site to Konza Prairie sites.
Keywords: land restoration; Plant cover; prairie; success monitoring; Vegetation analysis; vegetation sampling

Validation of a field-ready handheld meter for plasma β-hydroxybutyrate analysis - Sommers, Amie S.; W. A. Boyle; McGuire, Liam P. (Journal of Field Ornithology, 2017)
Plasma metabolite analysis is frequently used to assess the energetic state and energy intake of birds. Plasma β-hydroxybutyrate (BUTY) is a common metabolite used in these studies, and is correlated with fasting and mass loss. BUTY is typically quantified in laboratory assays that are costly, time-consuming, and prone to human error. We tested the accuracy and precision of a field-ready handheld BUTY meter. We compared BUTY concentration values obtained in the laboratory and with the handheld meter in plasma samples from 19 Grasshopper Sparrows (Ammodramus savannarum), and assessed precision with repeat analysis of a single sample. The handheld meter reported BUTY concentrations in < 2 min, was highly precise, and as accurate as the laboratory assay method—all ideal for field conditions. Collecting blood samples for laboratory analysis, particularly from remote field sites, involves a series of risks and challenges for permitting or the logistics of storage and shipping, as well as the associated costs. Analyzing samples on site, whether with the unit we tested or other similar handheld meters, makes plasma metabolite analysis practical and possible in field conditions and for taxa where this technique has been underused due to permitting, transport, or other logistical constraints of laboratory analysis methods. The cost of analysis is similar on a per sample basis, but, without the need to store and transport samples, using handheld meters in the field may be cheaper.

Above- and below-ground responses of native and invasive prairie grasses to future climate scenarios - E.B. Duell; G.T. Wilson; Hickman, K.R. (Botany, 2016)
More intense and frequent droughts, coupled with elevated temperatures, are projected for grasslands worldwide. Although it has been suggested that alterations in temperature and precipitation will increase the success of biological invasions, studies that combine these climate change scenarios are limited. These changes in climate may increase the success of non-native, invasive plant species directly, as these species often possess traits that are favored by variable climates, or indirectly through negative impacts on native vegetation or alterations in soil microbial communities, such as arbuscular mycorrhizal (AM) fungi. The goal of our research was to assess above- and below-ground production and mycorrhizal fungal abundance of functionally similar native and invasive non-native grass species under projected climate-change scenarios. We assessed plant biomass, intra-radical AM root colonization, and relative abundance of extra-radical fungal biomass of two native (Schizachyrium scoparium (Michx.) Nash, Pascopyrum smithii (Rydb.) Á.Löve) and two invasive (Bothriochloa ischaemum (L.) Keng, Bromus inermis Leyss.) grass species subjected to increased temperature and decreased soil water availability. Regardless of temperature or soil moisture, the invasive grasses in our study displayed greater seedling growth as compared with paired native species. Invasive grasses were also generally characterized by greater intra-radical colonization by AM fungi, compared with native species. Our data suggest that invasive grasses will continue to be problematic and successfully out-compete native grasses following increased temperatures and reduced water availability, as projected by climate-change models.
Keywords: Bothriochloa ischaemum; Bromus imermis; Climate change; Invasive species; Pascopyrum smithii; Schizachyrium scoparium

Addition of multiple limiting resources reduces grassland diversity - Harpole, W. S.; L.L. Sullivan; Lind, E.M.; Firn, J.; P. Adler; E.T. Borer; Chase, J.; Fay, P.A.; Hautier, Y.; Hillebrand, H.; MacDougall, A.S.; Seabloom, E.W.; et al. (Nature, 2016)
Niche dimensionality provides a general theoretical explanation for biodiversity—more niches, defined by more limiting factors, allow for more ways that species can coexist1. Because plant species compete for the same set of limiting resources, theory predicts that addition of a limiting resource eliminates potential trade-offs, reducing the number of species that can coexist2. Multiple nutrient limitation of plant production is common and therefore fertilization may reduce diversity by reducing the number or dimensionality of belowground limiting factors. At the same time, nutrient addition, by increasing biomass, should ultimately shift competition from belowground nutrients towards a one-dimensional competitive trade-off for light3. Here we show that plant species diversity decreased when a greater number of limiting nutrients were added across 45 grassland sites from a multi-continent experimental network4. The number of added nutrients predicted diversity loss, even after controlling for effects of plant biomass, and even where biomass production was not nutrient-limited. We found that elevated resource supply reduced niche dimensionality and diversity and increased both productivity5 and compositional turnover. Our results point to the importance of understanding dimensionality in ecological systems that are undergoing diversity loss in response to multiple global change factors.

Altered rainfall patterns increase forb abundance and richness in native tallgrass prairie - Jones, Sydney K.; Scott. L. Collins; John M. Blair; M.D. Smith; Alan K. Knapp (Scientific Reports, 2016)
Models predict that precipitation variability will increase with climate change. We used a 15-year precipitation manipulation experiment to determine if altering the timing and amount of growing season rainfall will impact plant community structure in annually burned, native tallgrass prairie. The altered precipitation treatment maintained the same total growing season precipitation as the ambient precipitation treatment, but received a rainfall regime of fewer, larger rain events, and longer intervals between events each growing season. Although this change in precipitation regime significantly lowered mean soil water content, overall this plant community was remarkably resistant to altered precipitation with species composition relatively stable over time. However, we found significantly higher forb cover and richness and slightly lower grass cover on average with altered precipitation, but the forb responses were manifest only after a ten-year lag period. Thus, although community structure in this grassland is relatively resistant to this type of altered precipitation regime, forb abundance in native tallgrass prairie may increase in a future characterized by increased growing season precipitation variability.

Assessing the potential for transitions from tallgrass prairie to woodlands: are we operating beyond critical transitions? - Z. Ratajczak; J. M. Briggs; Goodin, D.G.; Mohler, R.; Jesse B. Nippert; Obermeyer, B.K. (Rangeland Ecology & Management, 2016)
A growing body of evidence suggests humans are pushing ecosystems near or beyond key ecological thresholds, resulting in transitions to new, sometimes undesirable phases or states that are costly to reverse. We used remotely sensed fire data to assess if the Flint Hills—a landscape of tallgrass prairie in the Central Great Plains, United States—is operating beyond fire frequency thresholds. Long-term fire experiments and observational evidence suggests that applying prescribed fire at return intervals > 3 yr can lead to transitions from grassland to shrubland. Fire return intervals > 10 yr and complete fire suppression, in particular, can result in transitions to woodlands over 30 − 50 yr. Once shrublands and woodlands are established, restoration back to grassland is difficult with prescribed fires. We applied these fire frequency cutoffs to remotely sensed fire data from 2000 to 2010 in the Flint Hills, identifying the extent of tallgrass prairie susceptible to shrub and tree expansion. We found that 56% (15 620 km2) of grasslands in this region are burned less than every 3 yr and are therefore susceptible to conversion to shrub or tree dominance. The potential effects of this large-scale shift are greater risk for evergreen (Juniperus virginiana) woodland fires, reduced grazing potential, and increased abundance of woodland adapted species at the expense of the native grassland biota. Of the 12 127-km2 area likely to remain grassland, 43% is burned approximately annually, contributing to vegetative homogenization and potential air-quality issues. While this synthesis forecasts a precarious future for tallgrass prairie conservation and their ecosystem services, increases in shrub or tree dominances are usually reversible until fire frequency has been reduced for more than 20 yr. This delay leaves a small window of opportunity to return fire to the landscape and avoid large-scale transformation of tallgrass prairie.
Keywords: catastrophic shifts; forecasting; mesic grasslands; regime shifts; resilience; tipping points

Baseflow physical characteristics differ at multiple spatial scales in stream networks across diverse biomes - Rüegg, Janine; W. K. Dodds; Daniels, M.D.; Sheehan, Ken R.; Baker, Christina L.; W.B. Bowden; Farrell, Kaitlin J.; Flinn, Michael B.; Harms, Tamara K.; Jones, J.B.; Koenig, Lauren E.; Kominoski, John S.; et al. (Landscape Ecology, 2016)
Context Spatial scaling of ecological processes is facilitated by quantifying underlying habitat attributes. Physical and ecological patterns are often measured at disparate spatial scales limiting our ability to quantify ecological processes at broader spatial scales using physical attributes. Objective We characterized variation of physical stream attributes during periods of high biological activity (i.e., baseflow) to match physical and ecological measurements and to identify the spatial scales exhibiting and predicting heterogeneity. Methods We measured canopy cover, wetted width, water depth, and sediment size along transects of 1st–5th order reaches in five stream networks located in biomes from tropical forest to arctic tundra. We used hierarchical analysis of variance with three nested scales (watersheds, stream orders, reaches) to identify scales exhibiting significant heterogeneity in attributes and regression analyses to characterize gradients within and across stream networks. Results Heterogeneity was evident at one or multiple spatial scales: canopy cover and water depth varied significantly at all three spatial scales while wetted width varied at two scales (stream order and reach) and sediment size remained largely unexplained. Similarly, prediction by drainage area depended on the attribute considered: depending on the watershed, increases in wetted width and water depth with drainage area were best fit with a linear, logarithmic, or power function. Variation in sediment size was independent of drainage area. Conclusions The scaling of ecologically relevant baseflow physical characteristics will require study beyond the traditional bankfull geomorphology since predictions of baseflow physical attributes by drainage area were not always best explained by geomorphic power laws.
Keywords: Boreal forest; Geomorphology; Grasslands; Nested ANOVA; Scaling; Temperate forest

A before-and-after assessment of patch-burn grazing and riparian fencing along headwater streams - Larson, D.M.; W. K. Dodds; M.R. Whiles; .Thompson, T.R.; Fulgoni, J.N. (Journal of Applied Ecology, 2016)
Fire and grazing are common in grasslands world-wide to maintain grass cover and cattle production. The effects of fire, cattle grazing and riparian fencing efficacy on prairie stream ecology are not well characterized at catchment scales. We examined alterations to stream water quality and biology from patch-burn grazing (PBG) in tallgrass prairie during a five-year, replicated, catchment scale experiment that used a Before-After/Control-Impact (BACI) design and was analysed by mixed-effects models. Treatments included two patch-burned control catchments (fire but no grazers) and PBG in two riparian-fenced and two unfenced catchments. We assessed the effectiveness of riparian fencing for mitigating potential water quality impacts by monitoring water quality and riparian usage by cattle via Global Positioning System. Riparian fences effectively excluded cattle; however, in unfenced pastures, cattle aggregated along streams 10–20% of the grazing season. After initiation of PBG, we detected large increases in some nutrients, Escherichia coli, algal biomass, primary productivity and community respiration in all catchments with PBG. Some water quality variables, such as E. coli concentrations, recovered quickly after cattle were removed from pasture, which indicated resiliency. Riparian fencing moderately reduced the impacts to stream variables, indicating either overland flow and/or subsurface flow allowed nutrients and bacteria to enter the streams. Synthesis and applications. Patch-burn grazing is a measurable disturbance that can alter the ecological condition of streams. Riparian fencing lessened the degree of impact, yet some water quality variables still exceeded regional reference conditions. Managers will need to assess the costs of riparian fencing compared to the moderate benefits that fencing provides to water quality.

Belowground interactions with aboveground consequences: Invasive earthworms and arbuscular mycorrhizal fungi - Paudel, S.; Longcore, T.; MacDonald, B.; McCormick, M.K.; Szlavecz, K.; G.T. Wilson; Loss, S.R. (Ecology, 2016)
A mounting body of research suggests that invasive nonnative earthworms substantially alter microbial communities, including arbuscular mycorrhizal fungi (AMF). These changes to AMF can cascade to affect plant communities and vertebrate populations. Despite these research advances, relatively little is known about (1) the mechanisms behind earthworms’ effects on AMF and (2) the factors that determine the outcomes of earthworm–AMF interactions (i.e., whether AMF abundance is increased or decreased and subsequent effects on plants). We predict that AMF-mediated effects of nonnative earthworms on ecosystems are nearly universal because (1) AMF are important components of most terrestrial ecosystems, (2) nonnative earthworms have become established in nearly every type of terrestrial ecosystem, and (3) nonnative earthworms, due to their burrowing and feeding behavior, greatly affect AMF with potentially profound concomitant effects on plant communities. We highlight the multiple direct and indirect effects of nonnative earthworms on plants and review what is currently known about the interaction between earthworms and AMF. We also illustrate how the effects of nonnative earthworms on plant–AMF mutualisms can alter the structure and stability of aboveground plant communities, as well as the vertebrate communities relying on these habitats. Integrative studies that assess the interactive effects of earthworms and AMF can provide new insights into the role that belowground ecosystem engineers play in altering aboveground ecological processes. Understanding these processes may improve our ability to predict the structure of plant and animal communities in earthworm-invaded regions and to develop management strategies that limit the numerous undesired impacts of earthworms.

Beyond arctic and alpine: the influence of winter climate on temperate ecosystems - L. Ladwig; Z. Ratajczak; Ocheltree, T.W.; Hafich, K.A.; Churchill, A.C.; Frey, S.J.K.; Fuss, C.B.; Kazanski, C.E.; Muñoz, J.D.; Petrie, M.D.; Reinmann, A.B.; Smith, J.G. (Ecology, 2016)
Winter climate is expected to change under future climate scenarios, yet the majority of winter ecology research is focused in cold-climate ecosystems. In many temperate systems, it is unclear how winter climate relates to biotic responses during the growing season. The objective of this study was to examine how winter weather relates to plant and animal communities in a variety of terrestrial ecosystems ranging from warm deserts to alpine tundra. Specifically, we examined the association between winter weather and plant phenology, plant species richness, consumer abundance, and consumer richness in 11 terrestrial ecosystems associated with the U.S. Long-Term Ecological Research (LTER) Network. To varying degrees, winter precipitation and temperature were correlated with all biotic response variables. Bud break was tightly aligned with end of winter temperatures. For half the sites, winter weather was a better predictor of plant species richness than growing season weather. Warmer winters were correlated with lower consumer abundances in both temperate and alpine systems. Our findings suggest winter weather may have a strong influence on biotic activity during the growing season and should be considered in future studies investigating the effects of climate change on both alpine and temperate systems.

Bison and cattle grazing management, bare ground coverage, and links to suspended sediment concentrations in grassland streams - Grudzinski, B.P.; Daniels, M.D.; Anibas, K.; Spencer, D. (Journal of the American Water Resources Association, 2016)
This study quantified the impact of bison and cattle grazing management practices on bare ground coverage at the watershed, riparian, and forested riparian scales within the Flint Hills ecoregion in Kansas. We tested for correlations between bare ground coverage and fluvial suspended sediment concentrations during base-flow and storm-flow events. We used remotely sensed imagery combined with field surveys to classify ground cover and quantify the presence of bare ground. Base-flow water samples were collected bi-monthly during rain-free periods and 24 h following precipitation events. Storm-flow water samples were collected on the rising limb of the hydrograph, using single-stage automatic samplers. Ungrazed treatments contained the lowest coverage of bare ground at the watershed, riparian, and forested riparian scales. Bison treatments contained the highest coverage of bare ground at the watershed scale, while high-density cattle treatments contained the highest coverage of bare ground at the riparian and forested riparian scales. In bison and cattle-grazed treatments, a majority of bare ground was located near fence lines, watershed boundaries, and third- and fourth-order stream segments. Inorganic sediment concentrations at base flow were best predicted by riparian bare ground coverage, while storm-flow sediment concentrations were best predicted by watershed scale bare ground coverage.

Changes in soil properties, microbial biomass, and fluxes of C and N in soil following post-agricultural grassland restoration - Rosenzweig, S.T.; Carson, M.A.; S.G. Baer; John M. Blair (Applied Soil Ecology, 2016)
Understanding the dynamics of soil C and N pools and fluxes following grassland restoration in formerly cultivated soils is needed to assess the capacity of this land-use change to return soil properties and function to pre-disturbance conditions. We examined changes in physical (bulk density) and chemical (pH, available P and N, and total stocks of C and N) properties, microbial biomass C and N, and transformation rates of C and N in soil (0–10 cm depth) across a 35-year chronosequence of prairie restorations and never-cultivated (native) prairie to evaluate the rate and extent to which sowing native perennial plants into formerly cultivated soils returns soil to steady state conditions. Bulk density, available P, and extractable inorganic N decreased exponentially across the chronosequence. Soil pH increased linearly across the chronosequence to exceed that in native prairie soil. Total C and N stocks in cultivated soil were <50% that of native prairie, and increased at rates of 26.2 g C m−2 year−1 and 1.68 g N m−2 year−1 across the chronosequence. In the oldest restoration, total C and N stocks were 55% and 41% higher than the cultivated soil, respectively. Recovery of C and N stocks to levels comparable to native prairie soil was estimated to take 350 years. Microbial biomass C and N increased 5-fold. Potential C mineralization rate was comparable to native prairie soil following two decades of restoration, and exceeded native prairie in the 35-years restoration. In situ soil CO2 efflux reached equilibrium in <30 years. Potential net N mineralization rate, however, did not exhibit a directional change across the restoration chronosequence, but was lowest in the oldest restored grasslands. Thus, cessation of tillage and sowing native vegetation leads to rapid decreases in available N and P, and promotes rapid (decadal scale) recovery of labile soil organic matter pools, but recovery of total C and N pools requires several centuries. This study suggests that soil properties related to nutrient retention and regulation of nutrient availability can be reestablished within the first few decades of restoration, while C sequestration will continue on a longer time scale.
Keywords: Bulk density; chronosequence; soil respiration; SOM recovery; tallgrass prairie

Changes in spatial and temporal trends in wet, dry, warm and cold spell length or duration indices in Kansas, USA - Anandhi, Aavudai; Hutchinson, Stacy; Harrington, John; Rahmani, Vahid; Kirkham, Mary B.; C. W. Rice (International Journal of Climatology, 2016)

Characterizing organic matter inputs to sediments of small, intermittent, prairie streams: a molecular marker and stable isotope approach - Pisani, O.; W. K. Dodds; Jaffé, R. (Aquatic Sciences, 2016)
Small rivers and streams are ecologically important because they contribute to the export of organic carbon to coastal environments, likely influencing the global carbon cycle. While organic matter (OM) dynamics in large rivers has been studied in quite some detail, less is known about small streams. Sources of OM in streams ultimately determine its availability to the food web and downstream transport. In this study, sediment samples were collected from the King’s Creek watershed in Konza Prairie (Kansas, USA) and analyzed using molecular biomarkers and bulk 13C stable isotopes with the objective to comparatively assess OM inputs between riparian forest vegetation and watershed grassland to small, intermittent streams. We are interested in the potential influence of woody riparian expansion that has been ongoing at the site. Biomarkers typical of the local C4 grasses (branched n-alkanes, phytadienes) were more abundant in some of the sediments of the upper reaches. The sediments of the lower reaches contained biomarkers of algae (short-chain aliphatic compounds, C25:5 highly branched isoprenoid, brassicasterol) and vascular plant-derived material (triterpenols). Degraded OM (triterpene/triterpenol ratio) was found throughout the watershed with no pattern between the upper and lower reaches. Bulk 13C isotope analysis showed that the upper reaches of the watershed receive significant OM inputs from the C4 grasses (74–99 %) while the lower reaches are more strongly influenced by riparian trees (26–27 %) and algae (21–22 %). These results suggest that the environmental dynamics of bulk OM and the biomarker composition of small prairie streams are highly complex and likely a function of several factors such as light availability, riparian vegetative composition and density, and varying degrees of OM storage, retention and transport along the river continuum.
Keywords: 13C stable isotopes; Biomarkers; Konza Prairie; Riparian; Small streams; Watershed

Characterizing woody encroachment in the konza prairie using object-based analysis of aerial photographs - Shanko, A.R. (University of Kansas, 2016)
Woody encroachment is a threat to the ecological integrity of tallgrass prairie in Kansas.  Encroachment data that covers a large spatial and temporal scale would be valuable to managers of tallgrass prairie, but no such dataset exists.  The objective of this research is to develop a replicable technique for creating woody vegetation maps from aerial photographs.  Rather than using a traditional pixel-by-pixel approach to classification, this project uses an object-based approach, wherein individual pixels are grouped into meaningful image objects according to user-defined parameters and then classified.  I created woody vegetation maps of eight watersheds in the Konza Prairie using imagery from 1978, 1991, 2003, 2006, and 2010.  I also determined the efficacy of LIDAR data in classifying the image from 2006.  Ground-based vegetation survey data exist for two of the watersheds included in the remote sensing portion of this study.  I analyzed the data from the available years nearest to the imagery dates (1983, 1992, 2003, and 2007) in order to provide a measure of validation for the woody vegetation maps.  The results of this research were used to determine the applicability of this mapping technique and to draw preliminary conclusions about the landscape-level factors associated with woody encroachment.
Keywords: Flint Hills; Geographic information science and geodesy; Geography; Object-based image analysis; tallgrass prairie; woody encroachment

Climate modifies response of non-native and native species richness to nutrient enrichment - Flores-Moreno, H.; P.B. Reich; Lind, E.M.; L.L. Sullivan; Seabloom, E.W.; Yahdjian, L.; MacDougall, A.S.; Reichmann, L.G.; J. Alberti; Báez, S.; J.D. Bakker; Cadotte, M.W.; et al. (Philosophical Transactions of the Royal Society B: Biological Sciences, 2016)
Ecosystem eutrophication often increases domination by non-natives and causes displacement of native taxa. However, variation in environmental conditions may affect the outcome of interactions between native and non-native taxa in environments where nutrient supply is elevated. We examined the interactive effects of eutrophication, climate variability and climate average conditions on the success of native and non-native plant species using experimental nutrient manipulations replicated at 32 grassland sites on four continents. We hypothesized that effects of nutrient addition would be greatest where climate was stable and benign, owing to reduced niche partitioning. We found that the abundance of non-native species increased with nutrient addition independent of climate; however, nutrient addition increased non-native species richness and decreased native species richness, with these effects dampened in warmer or wetter sites. Eutrophication also altered the time scale in which grassland invasion responded to climate, decreasing the importance of long-term climate and increasing that of annual climate. Thus, climatic conditions mediate the responses of native and non-native flora to nutrient enrichment. Our results suggest that the negative effect of nutrient addition on native abundance is decoupled from its effect on richness, and reduces the time scale of the links between climate and compositional change.

codyn: An R package of community dynamics metrics - Hallett, L.M.; Jones, S.K.; MacDonald, A.A.M.; Jones, M.B.; Flynn, D.F.B.; Ripplinger, J.; Slaughter, P.; Gries, C.; Scott. L. Collins (Methods in Ecology and Evolution, 2016)
New analytical tools applied to long-term data demonstrate that ecological communities are highly dynamic over time. We developed an r package, library(“codyn”), to help ecologists easily implement these metrics and gain broader insights into ecological community dynamics. library(“codyn”) provides temporal diversity indices and community stability metrics. All functions are designed to be easily implemented over multiple replicates. Temporal diversity indices include species turnover, mean rank shifts and rate of community change over time. Community stability metrics calculate overall stability and patterns of species covariance and synchrony over time, and include a null-modelling method to test significance. Finally, library(“codyn”) contains vignettes that describe methods and reproduce figures from published papers to help users contextualize and apply functions to their own data.

Comparative ecohydrology between Cornus drummondii and Solidago canadensis in upland tallgrass prairie - Muench, A.; O'Keefe, K.; Jesse B. Nippert (Plant Ecology, 2016)
Woody species expansion threatens to transform mesic North American grasslands. In many tallgrass prairies of the central Great Plains with deep soil, Cornus drummondii develops large shrub islands that exhibit non-linear increases in cover through time. Reliance on soil moisture from deeper soil depths facilitates constant gas exchange rates and minimizes competition with coexisting herbaceous species. Conversely, C. drummondii growth and expansion in thin-soil locations is stochastic and these locations are typically free of large shrub islands. At the Konza Prairie in northeast Kansas, USA, we compared the ecohydrology of C. drummondii individuals to a similar-sized forb (Solidago canadensis) in thin-soil locations with varying fire frequency (4-, 20-year) and grazer abundance (bison present or absent). Gas exchange rates were relatively constant for C. drummondii, while S. canadensis declined across the growing season. For S. canadensis, maximum photosynthesis (Amax), daytime transpiration (E), and stomatal conductance (gs) were higher on ungrazed than grazed treatments. Nighttime E rates were higher in C. drummondii, accounting for over 10 % of the daytime E rates. The water source used did not vary among contrasts, with the majority of water uptake occurring from 30 cm depth for both species. These results highlight a unique ecohydrology of C. drummondii (static water flux, and high rates of nighttime E) compared to a similar-sized, co-occurring forb. Whereas C. drummondii is infrequent in thin-soil locations, the climate conditions occurring during measurements were not a likely filter restricting persistence. Rather, drier conditions or interactions with other grassland disturbances are likely required to restrict C. drummondii encroachment in the thins-soil locations of tallgrass prairie.
Keywords: Konza Prairie; Mesic grassland; photosynthesis; Stable water isotopes; Transpiration; woody encroachment

Co-variation in methanotroph community composition and activity in three temperate grassland soils - Judd, Craig R.; Koyama, Akihiro; Simmons, Mark P.; Brewer, Paul; von Fischer, Joseph C. (Soil Biology and Biochemistry, 2016)
Methane is a potent greenhouse gas, and the uptake of methane by methanotrophic bacteria in oxic, well-drained soils is a key global sink. Field studies at the ecosystem scale have observed significant temporal and spatial variation in methane uptake rates, but there is considerable uncertainty about the roles of abiotic and biotic factors, including methanotroph community composition, in structuring these patterns. Here, we present an analysis of Michaelis–Menten kinetics of methane uptake in soils collected from three North American temperate grassland sites of differing soil moisture regimes and their methanotroph community composition. The three sites were Konza Prairie in Kansas, Shortgrass Steppe in Colorado and Sevilleta in New Mexico with mean annual precipitation of 835, 320 and 244 mm, respectively. Michaelis–Menten kinetics and methanotroph community were assessed via lab incubation and pmoA-based phylogeny, respectively. Across the precipitation gradient we observed distinct variation in Michaelis–Menten kinetics and methanotroph community composition. Both KM and VMax values of the Michaelis–Menten kinetics followed the trend of the mean annual precipitation (Konza Prairie > Shortgrass Steppe > Sevilleta). The observed six methanotroph clades were all within the γ-proteobacteria division, and included two novel clades found in Shortgrass Steppe and Sevilleta. The methanotroph communities were dominated by Methylococcus spp, JR2 clade, and USC gamma, in Konza Prairie, Shortgrass Steppe and Sevilleta soils, respectively. The distinct differences in the community composition among the three sites may help explain the functional variation of upland methanotrophy observed in KM. Taken together, the coincident differences in Michaelis–Menten kinetics we observed suggest that methanotroph community composition can be important for CH4 uptake in controlled environments, potentially playing a role in the variation in methane uptake in the fields.
Keywords: Grassland soils; Methanotroph community composition; Methanotroph phylogeny; Michaelis–Menten kinetics

Crab spiders (Thomisidae) attract insect flower-visitors without UV signaling - Welti, E.; Putnam, S.; Anthony Joern (Ecological Entomology, 2016)
1. Crab spiders (Thomisidae) indirectly affect insect flower-visitor and flowering plant interactions by consuming and altering the behaviour of insects. 2. Although one expects insect flower-visitors to avoid crab spiders actively, some crab spider species are known to attract flower-visitors. Crab spiders may use UV signalling to lure potential prey to the flowers they occupy. 3. In the present study, a field experiment was conducted to examine the effects of crab spiders occupying three prairie plant species for the insect flower-visitor community. Pollinating insects were significantly attracted to inflorescences with crab spiders compared to inflorescences without crab spiders for two plant species, and herbivorous insects were attracted to inflorescences with crab spiders for one of these plant species. The two flowering plant species with increased pollinator visitation showed increased seed weights for plants with crab spiders, indicating crab spider presence indirectly increased pollination. 4. To test the UV signalling hypothesis, inflorescences with crab spiders of one plant species were observed under both a UV-blocking plastic and a clear plastic control. Contrary to our prediction, flower-visitors were not more likely to land on inflorescences under the clear plastic; the UV signalling hypothesis was not supported. Other unknown explanations underlie prey attraction to inflorescences with crab spiders.

Does ecosystem sensitivity to precipitation at the site-level conform to regional-scale predictions? - K.R. Wilcox; John M. Blair; M.D. Smith; Alan K. Knapp (Ecology, 2016)
Central to understanding global C cycle dynamics is the functional relationship between precipitation and net primary production (NPP). At large spatial (regional) scales, the responsiveness of aboveground NPP (ANPP) to inter-annual variation in annual precipitation (AP; ANPPsensitivity) is inversely related to site-level ANPP, coinciding with turnover of plant communities along precipitation gradients. Within ecosystems experiencing chronic alterations in water availability, plant community change will also occur with unknown consequences for ANPPsensitivity. To examine the role plant community shifts may play in determining alterations in site-level ANPPsensitivity, we experimentally increased precipitation by ~35% for two decades in a native Central US grassland. Consistent with regional models, ANPPsensitivity decreased initially as water availability and ANPP increased. However, ANPPsensitivity shifted back to ambient levels when mesic species increased in abundance in the plant community. Similarly, in grassland sites with distinct mesic and xeric plant communities and corresponding 50% differences in ANPP, ANPPsensitivity did not differ over almost three decades. We conclude that responses in ANPPsensitivity to chronic alterations in water availability within an ecosystem may not conform to regional AP-ANPP patterns, despite expected changes in ANPP and plant communities. The result is unanticipated functional resistance to climate change at the site scale.

Drivers of variation in aboveground net primary productivity and plant community composition differ across a broad precipitation gradient - Kimberly J. La Pierre; D.M. Blumenthal; C.S. Brown; Klein, J.A.; M.D. Smith (Ecosystems, 2016)
Aboveground net primary production (ANPP) is a key integrator of C uptake and energy flow in many terrestrial ecosystems. As such, ecologists have long sought to understand the factors driving variation in this important ecosystem process. Although total annual precipitation has been shown to be a strong predictor of ANPP in grasslands across broad spatial scales, it is often a poor predictor at local scales. Here we examine the amount of variation in ANPP that can be explained by total annual precipitation versus precipitation during specific periods of the year (precipitation periods) and nutrient availability at three sites representing the major grassland types (shortgrass steppe, mixed-grass prairie, and tallgrass prairie) spanning the broad precipitation gradient of the U.S. Central Great Plains. Using observational data, we found that precipitation periods and nutrient availability were much stronger predictors of site-level ANPP than total annual precipitation. However, the specific nutrients and precipitation periods that best predicted ANPP differed among the three sites. These effects were mirrored experimentally at the shortgrass and tallgrass sites, with precipitation and nutrient availability co-limiting ANPP, but not at the mixed-grass site, where nutrient availability determined ANPP exclusive of precipitation effects. Dominant grasses drove the ANPP response to increased nutrient availability at all three sites. However, the relative responses of rare grasses and forbs were greater than those of the dominant grasses to experimental nutrient additions, thus potentially driving species turnover with chronic nutrient additions. This improved understanding of the factors driving variation in ANPP within ecosystems spanning the broad precipitation gradient of the Great Plains will aid predictions of alterations in ANPP under future global change scenarios.
Keywords: dominant species; Great Plains; Nutrient Network (NutNet); nutrients; precipitation periods; rare species

Ecohydrological and climate change studies at the Konza Prairie Biological Station - J. M. Briggs; John M. Blair; Horne, E.A. (Transactions of the Kansas Academy of Science, 2016)

The effect of timing of growing season drought on flowering of a dominant C4 grass - Dietrich, J.D.; M.D. Smith (Oecologia, 2016)
Timing of precipitation is equally important as amount for determining ecosystem function, especially aboveground net primary productivity (ANPP), in a number of ecosystems. In tallgrass prairie of the Central Plains of North America, grass flowering stalks of dominant C4 grasses, such as Andropogon gerardii, can account for more than 70 % of ANPP, or almost none of it, as the number of flowering stalks produced is highly variable. Although growing season precipitation amount is important for driving variation in flowering stalk production, it remains unknown whether there are critical periods within the growing season in which sufficient rainfall must occur to allow for flowering. The effect of timing of rainfall deficit (drought) on flowering of A. gerardii, was tested by excluding rainfall during three periods within the growing season (starting in mid-April, mid-May and mid-June). Mid-summer drought (starting in mid-June) strongly reduced the flowering rate (e.g., density and biomass) of A. gerardii (e.g., as high as 94 % compared to the control), suggesting flowering is highly sensitive to precipitation at this time. This effect appeared to be related to plant water status at the time of flowering stalk initiation, rather than an indirect consequence of reduced C assimilation. Our results suggest that increased frequency of growing season drought forecast with climate change could reduce sexual reproduction in this dominant grass species, particularly if it coincides with timing of flowering stalk initiation, with important implications for ecosystem functioning.
Keywords: Aboveground net primary productivity; Andropogon gerardii; Ecophysiology; Precipitation timing; tallgrass prairie

The effects of P fertilizer addition on P transformations on high-P fixing and grassland soils - Pierzynski, Joy (Kansas State University, 2016)
Although phosphorus (P) is an essential nutrient for the growth of plants, it is one of the most limiting nutrients in terms of availability as a high proportion of applied P rapidly transforms into insoluble forms with low solubility in soils. To further understand the fate of P applied to soils, two separate but related studies using three high P-fixing soil types each were used for which the objectives were to investigate the mobility, availability, and reaction products from two granular and one liquid P fertilizer alone or plus a fertilizer enhancement product. Energy dispersive spectroscopy showed a substantial amount of P remained in the granule following a 5-week incubation. At the end of the 35-day incubation period there was evidence that the fluid fertilizer was superior over the granular sources in terms of enhanced diffusion and extractability of P for three calcareous soils with varying levels of CaCO₃. Phosphorus x-ray absorption near-edge structure (XANES) spectroscopy results in conjunction with resin-extractable P indicated a strong negative correlation between Ca-P solids formed and P extractability, suggesting that degree of Ca-P formation limits P solubility. For the three acidic P-fixing soils the results were complex. In two out of three acid soils, liquid P treatments diffused farther from the application point than the granular treatments. Phosphorus XANES results suggested that Fe-P or Al-P interactions control the overall P solubility. Integration of pH, resin extractable-P and XANES results suggested the P retention mechanism was either dominated by adsorption or precipitation depending on soil pH. More acidic soil conditions favored precipitation. The objectives of the third study were to observe how long-term (14 years) addition of P with or without N influences the inorganic and organic P pools in a native grassland soil using sequential fractionation, XANES, and ³¹P-nuclear magnetic resonance (NMR) spectroscopy. The overall results suggested that P and N fertilization and associated changes in plant productivity induced significant changes in soil P pools such as Ca-P, phytic acid, monoesters, and residual forms of P. The addition of P alone induced formation of inorganic P forms while the addition of P and N induced transformation of residual P forms into more labile and/or organic P forms.
Keywords: High phosphorus-fixing acid soil; High phosphorus-fixing calcareous soil; High phosphorus-fixing soil; Soil phosphorus; Soil phosphorus cycle; Tall grassland soils

Environmental extremes drive plant and soil community dynamics of native and disturbed grasslands - Zaiger, K. (Oklahoma State University, 2016)

Environmental heterogeneity has a weak effect on diversity during community assembly in tallgrass prairie - S.G. Baer; John M. Blair; Scott. L. Collins (Ecological Monographs, 2016)
Understanding what constrains the persistence of species in communities is at the heart of community assembly theory and its application to conserving and enhancing biodiversity. The “environmental heterogeneity hypothesis” predicts greater species coexistence in habitats with greater resource variability. In the context of community assembly, environmental heterogeneity may influence the variety and strength of abiotic conditions and competitive interactions (environmental filters) to affect the relative abundance of species and biodiversity. We manipulated key resources that influence plant diversity in tallgrass prairie (i.e., soil depth and nitrogen availability) to increase environmental heterogeneity prior to sowing native prairie species into a former agricultural field. We compared variability in nutrient availability, aboveground annual net primary productivity (ANPP), and the composition of species between replicate plots containing soil heterogeneity manipulations and plots with no resource manipulations (n = 4 per treatment) during the first 15 yr of community assembly as a test of the “environmental heterogeneity hypothesis.” The manipulations increased environmental heterogeneity, measured as the coefficient of variation in NO3-N availability and ANPP. Plant diversity, however, was similar and decayed exponentially and indiscriminately over time between the heterogeneity treatments. Species richness declined linearly over time in both heterogeneity treatments, but richness was higher in the more heterogeneous soil 2 yr following a second propagule addition 8 yr after the initial sowing. As a result, there was a lower rate of species loss over time in the more heterogeneous soil (0.60 species yr−1) relative to the control soil (0.96 species yr−1). Communities in each treatment exhibited strong convergence over time resulting from a shift in dominant species across all treatments and a gradual increase in the clonal C4 grass, Andropogon gerardii. We attribute the weak effect of heterogeneity on diversity to increasing dominance of a clonal species, which decreased the scale of soil treatments relative to plant size, dispersal limitation, and absence of a key driver (grazing) known to increase plant diversity under a frequent fire regime. Thus, steering community assembly to attain high biodiversity may depend more on manipulating processes that reduce dominance and facilitate the arrival of new species than promoting environmental heterogeneity.

Few multiyear precipitation–reduction experiments find a shift in the productivity–precipitation relationship - Estiarte, M.; Vicca, S.; Peñuelas, J.; Michael Bahn; Beier, C.; Emmett, B.A.; Fay, P.A.; Hanson, P.J.; R. Hasibeder; Kigel, J.; Kröel-Dulay, G.; Larsen, K.S.; et al. (Global Change Biology, 2016)
Well-defined productivity–precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity–precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation–reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation–manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity–precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation–reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid.

The first to arrive and the last to leave: colonisation and extinction dynamics of common and rare fishes in intermittent prairie streams - Whitney, J.E.; K. B. Gido; Martin, E.C.; Hase, K.J. (Freshwater Biology, 2016)
1. The objectives of our research were to examine commonness–rarity patterns in fish communities in networks of intermittent streams. We quantified species abundance distributions and the importance of nestedness and turnover to community dissimilarity and then related commonness to colonisation, extinction and physiological tolerance. Patterns and relationships were evaluated spatially among sites and temporally within sites during non-drought and drought periods in tallgrass prairie streams of eastern Kansas, U.S.A. 2. Supra-seasonal drought during 2011–2013 resulted in complete or partial drying of some sites and provided an opportunity to evaluate whether commonness was predictive of rather than predicted by colonisation and extinction. Abundance was used to predict re-colonisation in desiccated reaches and persistence in drying pools. 3. Few species were common, while most were rare regardless of drought, and nestedness drove community dissimilarity across sites. Common species had higher colonisation and lower extinction than rarer species, but physiological tolerance was unrelated to commonness. 4. Abundant species were generally the first to re-colonise desiccated reaches, but pre-drought abun-dance did not predict persistence in partially desiccated reaches. 5. Although common species were the first to colonise and the last to go extinct, we were unable to determine whether commonness was predictive of rather than predicted by colonisation and extinc-tion. Regardless, our study demonstrates linkages among commonness, colonisation and extinction.

Foraging decisions underlying restricted space use: effects of fire and forage maturation on large herbivore nutrient uptake - Raynor, E.J.; Anthony Joern; Jesse B. Nippert; J. M. Briggs (Ecology and Evolution, 2016)
Recent models suggest that herbivores optimize nutrient intake by selecting patches of low to intermediate vegetation biomass. We assessed the application of this hypothesis to plains bison (Bison bison) in an experimental grassland managed with fire by estimating daily rates of nutrient intake in relation to grass biomass and by measuring patch selection in experimental watersheds in which grass biomass was manipulated by prescribed burning. Digestible crude protein content of grass declined linearly with increasing biomass, and the mean digestible protein content relative to grass biomass was greater in burned watersheds than watersheds not burned that spring (intercept; F1,251 = 50.57, P < 0.0001). Linking these values to published functional response parameters, ad libitum protein intake, and protein expenditure parameters, Fryxell's (Am. Nat., 1991, 138, 478) model predicted that the daily rate of protein intake should be highest when bison feed in grasslands with 400–600 kg/ha. In burned grassland sites, where bison spend most of their time, availability of grass biomass ranged between 40 and 3650 kg/ha, bison selected foraging areas of roughly 690 kg/ha, close to the value for protein intake maximization predicted by the model. The seasonal net protein intake predicted for large grazers in this study suggest feeding in burned grassland can be more beneficial for nutrient uptake relative to unburned grassland as long as grass regrowth is possible. Foraging site selection for grass patches of low to intermediate biomass help explain patterns of uniform space use reported previously for large grazers in fire-prone systems.

Gene expression patterns of two dominant tallgrass prairie species differ in response to warming and altered precipitation - M.D. Smith; Hoffman, A.M.; M.L. Avolio (Scientific Reports, 2016)
To better understand the mechanisms underlying plant species responses to climate change, we compared transcriptional profiles of the co-dominant C4 grasses, Andropogon gerardii Vitman and Sorghastrum nutans (L.) Nash, in response to increased temperatures and more variable precipitation regimes in a long-term field experiment in native tallgrass prairie. We used microarray probing of a closely related model species (Zea mays) to assess correlations in leaf temperature (Tleaf) and leaf water potential (LWP) and abundance changes of ~10,000 transcripts in leaf tissue collected from individuals of both species. A greater number of transcripts were found to significantly change in abundance levels with Tleaf and LWP in S. nutans than in A. gerardii. S. nutans also was more responsive to short-term drought recovery than A. gerardii. Water flow regulating transcripts associated with stress avoidance (e.g., aquaporins), as well as those involved in the prevention and repair of damage (e.g., antioxidant enzymes, HSPs), were uniquely more abundant in response to increasing Tleaf in S. nutans. The differential transcriptomic responses of the co-dominant C4 grasses suggest that these species may cope with and respond to temperature and water stress at the molecular level in distinct ways, with implications for tallgrass prairie ecosystem function.

Grasshopper sparrows on the move: patterns and causes of within-season breeding dispersal in a declining grassland songbird - Williams, E.J. (Kansas State University, 2016)

High dissimilarity within a multiyear annual record of pollen assemblages from a North American tallgrass prairie - Commerford, J.L.; McLauchlan, K.K.; Minckley, T.A. (Ecology and Evolution, 2016)
Grassland vegetation varies in composition across North America and has been historically influenced by multiple biotic and abiotic drivers, including fire, herbivory, and topography. Yet, the amount of temporal and spatial variability exhibited among grassland pollen assemblages, and the influence of these biotic and abiotic drivers on pollen assemblage composition and diversity has been relatively understudied. Here, we examine 4 years of modern pollen assemblages collected from a series of 28 traps at the Konza Prairie Long‐Term Ecological Research Area in the Flint Hills of Kansas, with the aim of evaluating the influence of these drivers, as well as quantifying the amount of spatial and temporal variability in the pollen signatures of the tallgrass prairie biome. We include all terrestrial pollen taxa in our analyses while calculating four summative metrics of pollen diversity and composition – beta‐diversity, Shannon index, nonarboreal pollen percentage, and Ambrosia:Artemisia – and find different roles of fire, herbivory, and topography variables in relation to these pollen metrics. In addition, we find significant annual differences in the means of three of these metrics, particularly the year 2013 which experienced high precipitation relative to the other 3 years of data. To quantify spatial and temporal dissimilarity among the samples over the 4‐year study, we calculate pairwise squared‐chord distances (SCD). The SCD values indicate higher compositional dissimilarity across the traps (0.38 mean) among all years than within a single trap from year to year (0.31 mean), suggesting that grassland vegetation can have different pollen signatures across finely sampled space and time, and emphasizing the need for additional long‐term annual monitoring of grassland pollen.
Keywords: fire; grassland; Great Plains; Herbivory; Pollen; Tauber traps

The immediate and prolonged effects of climate extremes on soil respiration in a mesic grassland - Hoover, D.L.; Alan K. Knapp; M.D. Smith (Journal of Geophysical Research: Biogeosciences, 2016)
The predicted increase in the frequency and intensity of climate extremes is expected to impact terrestrial carbon fluxes to the atmosphere, potentially changing ecosystems from carbon sinks to sources, with positive feedbacks to climate change. As the second largest terrestrial carbon flux, soil CO2 efflux or soil respiration (Rs) is strongly influenced by soil temperature and moisture. Thus, climate extremes such as heat waves and extreme drought should have substantial impacts on Rs. We investigated the effects of such climate extremes on growing season Rs in a mesic grassland by experimentally imposing 2 years of extreme drought combined with midsummer heat waves. After this 2 year period, we continued to measure Rs during a recovery year. Two consecutive drought years reduced Rs by about 25% each growing season; however, when normal rainfall returned during the recovery year, formerly droughted plots had higher rates of Rs than control plots (up to +17%). The heat wave treatments had no effect on Rs, alone or when combined with drought, and during the growing season, soil moisture was the primary driver of Rs with little evidence for Rs temperature sensitivity. When compared to aboveground net primary production, growing season Rs was much less sensitive to drought but was more responsive postdrought. These results are consistent with the hypothesis that ecosystems become sources of CO2 during drought because carbon inputs (production) are decreased relatively more than outputs (respiration). Moreover, stimulation of Rs postdrought may lengthen the time required for net carbon exchange to return to predrought levels.

Importance of vegetation structure to the assembly of an aerial web-building spider community in North American open grassland - Gómez, Jesús E.; Lohmiller, Jenny; Anthony Joern (Journal of Arachnology, 2016)
Spatial and temporal heterogeneity of suitable habitat in grasslands can promote species and functional diversity in arthropods, including responses by ubiquitous web-building spiders. A field experiment in tallgrass prairie habitat was performed to examine the response in abundance and web-type richness of aerial web-building spiders to changes in the availability of structure for web placement (vegetation architecture). To test the hypothesis that vegetation structure contributes directly to the web-builder abundance and web-type richness in open grasslands, we increased vegetation structure by adding dead woody stems of a common shrub along transects in each of three watersheds that differed in burn histories and existing habitat structure. Aerial web-building spiders were visually censused before and after the manipulations, at which time we recorded web-orientation, height, web-type, and the presence/absence of the spider associated with a web. Over the duration of the study, a total of seven web-type groups were encountered, of which medium-sized orb weavers were the most abundant web-building group across all watersheds. In general, higher spider abundances of orb-building spiders were observed in sections with added structure compared to the non-manipulated sections. However, reduced richness of web types was found on the manipulated sections of transects, suggesting that the architecture provided by woody stems does not provide sufficient and appropriate web-anchoring structure for the full range of web-building spiders groups in tallgrass prairie.
Keywords: habitat structure; heterogeneity–biodiversity hypothesis; Konza; tallgrass prairie; Web types

Increasing fish taxonomic and functional richness affects ecosystem properties of small headwater prairie streams - Martin, E.D.; K. B. Gido; Bello, N.; W. K. Dodds; Veach, A.M. (Freshwater Biology, 2016)
1. Stream fish can regulate their environment through direct and indirect pathways, and the relative influence of communities with different taxonomic and functional richness on ecosystem properties likely depends on habitat structure. Given this complexity, it is not surprising that observational studies of how stream fish communities influence ecosystems have shown mixed results. 2. In this study, we evaluated the effect of an observed gradient of taxonomic (zero, one, two or three species) and functional (zero, one or two groups) richness of fishes on several key ecosystem properties in experimental stream mesocosms. Our study simulated small (less than two metres wide) headwater prairie streams with a succession of three pool-riffle structures (upstream, middle and downstream) per mesocosm. Ecosystem responses included chlorophyll a from floating algal mats and benthic algae, benthic organic matter, macroinvertebrates (all as mass per unit area), algal filament length and stream metabolism (photosynthesis and respiration rate). Ecosystem responses were analysed individually using general linear mixed models. 3. Significant treatment (taxonomic and functional richness) by habitat (pools and riffles) interactions were found for all but one ecosystem response variable. After accounting for location (upstream, middle and downstream) effects, the presence of one or two grazers resulted in shorter mean algal filament lengths in pools compared to no-fish controls. These observations suggest grazers can maintain short algal filaments in pools, which may inhibit long filaments from reaching the surface. Accordingly, floating algal mats decreased in mid- and downstream locations in grazer treatment relative to no-fish controls. 4. At the scale of the entire reach, gross primary productivity and respiration were greater in treatments with two grazer species compared to mixed grazer/insectivore or control treatments. 5. The distribution of stream resources across habitat types and locations within a reach can therefore be influenced by the taxonomic and functional composition of fishes in small prairie streams. Thus, disturbances that alter diversity of these systems might have unexpected ecosystem-level consequences.

Influence of productivity and disturbance on plant species diversity across the grasslands of the great plains - Mcconaghy, S.C. (Texas AM University, 2016)

Integrative modelling reveals mechanisms linking productivity and plant species richness - Grace, J.B.; Anderson, T.M.; Seabloom, E.W.; E.T. Borer; P. Adler; Harpole, W.S.; Hautier, Y.; Hillebrand, H.; Lind, E.M.; Pärtel, M.; J.D. Bakker; Buckley, Y.M.; et al. (Nature, 2016)
How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology1. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns2, 3. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models4, 5, 6, 7. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis8, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.

Investigating North American grassland biogeography throughout the Holocene - Commerford, J.L. (Kansas State University, 2016)

Mechanisms driving the soil organic matter decomposition response to nitrogen enrichment in grassland soils - Riggs, C.E.; Hobbie, S.E. (Soil Biology and Biochemistry, 2016)
Empirical studies show that nitrogen (N) addition often reduces microbial decomposition of soil organic matter (SOM) and carbon dioxide (CO2) production via microbial respiration. Although predictions from theoretical models support these findings, the mechanisms that drive this response remain unclear. To address this uncertainty, we sampled soils of three grassland sites in the U.S. Central Great Plains that each have received seven years of continuous experimental nutrient addition in the field. Nitrogen addition significantly decreased the decomposition rate of slowly cycling SOM and the cumulative carbon (C) respired per mass soil C. We evaluated whether this effect of N addition on microbial respiration resulted from: 1) increased microbial carbon use efficiency (CUE), 2) decreased microbial oxidative enzyme activity, or 3) decreased microbial biomass due to plant and/or soil mediated responses to N enrichment. In contrast to our hypotheses – as well as results from N addition studies in forest ecosystems and theoretical predictions – N did not increase microbial CUE or decrease microbial oxidative enzyme activity. Instead, reduced microbial biomass likely caused the decreased respiration in response to N enrichment. Identifying what factors drive this decreased microbial biomass response to N should be a priority for further inquiry.
Keywords: carbon; Fertilization; Microbial biomass; Microbial respiration; Nutrient Network

Methods of approximation influence aquatic ecosystem metabolism estimates - Song, Chao; W. K. Dodds; Trentman, Matt T.; Rüegg, Janine; Ballantyne, Ford (Limnology and Oceanography: Methods, 2016)
Aquatic ecologists have recently employed dynamic models to estimate aquatic ecosystem metabolism. All approaches involve numerically solving a differential equation describing dissolved oxygen (DO) dynamics. Although the DO differential equation can be solved accurately with linear multistep or Runge–Kutta methods, less accurate methods, such as the Euler method, have been applied. The methods also differ in how discrete temperature and light measurements are used to drive DO dynamics. Here, we used a representative stream DO data set to compare the metabolism estimates generated by multiple Euler based methods and an accurate numerical method. We also compared metabolism estimates using linear, piecewise constant and smoothing spline interpolation of light and temperature. Using observed DO to calculate DO saturation deficit in the Euler method results in a substantial difference in metabolism estimates compared to all other methods. If modeled DO is used to calculate DO saturation deficit, the Euler method introduces smaller error in metabolism estimates, which diminishes as logging interval decreases. Linear and smoothing spline interpolation result in similar metabolism estimates, but differ from estimates based on piecewise constant interpolation. We demonstrate how different computational methods imply distinct assumptions about process and observation error, and conclude that under the assumption of observation error, the best practice is to use the accurate numerical method of solving differential equation with a continuous interpolation of light and temperature. The Euler method will introduce minimal error if it is paired with frequently logged data and DO saturation deficit is computed using modeled DO.

A multi-scale examination of the distribution and habitat use patterns of the regal fritillary - McCullough, Kelsey.E. (Kansas State University, 2016)

Nitrogen, phosphorus, and eutrophication in streams - W. K. Dodds; Smith, V.H. (Inland Waters, 2016)
Flowing waters receive substantial nutrient inputs, including both nitrogen (N) and phosphorus (P), in many parts of the world. Eutrophication science for rivers and streams has unfortunately lagged behind that for lakes, and results from lakes might inform those interested in stream eutrophication. A key controversy in lake eutrophication science is the relative importance of controlling P and N in water quality management, and we are interested how the science of this controversy transfers to flowing waters. A literature review indicates (1) stream benthic chlorophyll is significantly correlated to both total N and total P in the water column, with both nutrients explaining more variance than either considered alone; (2) nutrients have increased substantially in many rivers and streams of the United States over reference conditions, and strong shifts in N and P stoichiometry have occurred as well; (3) bioassays often indicate N responses alone or in concert with P responses for autotrophic (primary production and chlorophyll) and heterotrophic (respiration) responses; (4) both heterotrophic and autotrophic processes are influenced by the availability of N and P; and (5) N-fixing cyanobacteria usually do not seem to be able to fully satisfy N limitations in rivers and streams when P is present in excess of N. These data suggest both N and P control should be considered in the eutrophication management of streams.
Keywords: eutrophication; nitrogen; Phosphorus; streams

Nutrient additions cause divergence of tallgrass prairie plant communities resulting in loss of ecosystem stability - Koerner, S.E.; M.L. Avolio; Kimberly J. La Pierre; K.R. Wilcox; M.D. Smith; Scott. L. Collins (Journal of Ecology, 2016)
1.Nitrogen (N) and phosphorus (P) deposition due to pollution and land-use change are dramatically altering biogeochemical cycles. These altered nutrient inputs affect plant communities by generally increasing dominance and reducing diversity, as well as altering community variability (heterogeneity). Less well studied are effects of changes in community variability on ecosystem functions, such as productivity, or the stability of those functions. 2.Here we use a twelve-year nutrient addition experiment in tallgrass prairie to determine variability in community responses to N and P additions and link these responses to ecosystem productivity and stability. We added two levels of N and four levels of P in a fully factorial design to 25-m2 plots in native tallgrass prairie in northeastern Kansas, USA. Each year percent cover of each species was measured in June and August in a 1-m2 subplot of each plot, and annual net primary productivity was measured in two 0.1-m2 subplots in each plot at the end of each growing season. 3.The addition of N and P together increased plant community variability across space (i.e., the replicates were significantly more different from each other in the N + P treatments than they were in the control treatment). We also found that variability of the plant community within a single plot through time increased with the addition of N alone and N and P together. The highest level of both spatial and temporal variability occurred in plots with the highest level of nutrient addition (10 g m−2 of both N and P). 4.While we found no linkage between spatial variability of community composition and the spatial stability of productivity, the temporal stability of productivity decreased with increasing temporal plant community variability. Additionally, the ability to predict the productivity response to growing season precipitation, a key environmental variable, also decreased under higher temporal community variability. 5.Synthesis. Using a 12-yr nutrient addition experiment, we found that nutrient addition leads to both spatial and temporal community variability in mesic tallgrass prairie. The changes in community variability through time were directly related to ecosystem stability. While overall shifts in community structure in response to nutrient additions are important, the change in variability of local communities has significant implications for our ability to predict how patterns of biodiversity and ecosystem function will respond to a rapidly changing world.

Of mice and coyotes: mammalian responses to rangeland management practices in tallgrass prairie - Ricketts, A.M. (Kansas State University, 2016)

Patch-burn grazing increases habitat heterogeneity and biodiversity of small mammals in managed rangelands - Ricketts, A.M.; Sandercock, B.K. (Ecosphere, 2016)
Habitat heterogeneity is a key driver of biodiversity in many ecosystems. Wildlife inhabiting the native prairies of North America evolved in a heterogeneous mosaic of habitat conditions created by fire and grazing by native ungulates. Current rangeland management practices in the tallgrass prairie ecosystem evenly distribute fire and grazing across management units and promote homogeneous habitat conditions. Patch-burn grazing is a rangeland management strategy that seeks to restore heterogeneity to rangelands via fire-grazing interactions. Our 3.5-year study tested the effects of patch-burn grazing on habitat heterogeneity and small mammal community dynamics in the Flint Hills ecoregion of eastern Kansas. To study the ecological effects of patch-burn grazing, we sampled habitat conditions and the small mammal community. We assessed habitat conditions once each growing season in a negative control that was annually burned and grazed, a positive control that was burned every four years and ungrazed, and within each of three units of a patch-burn grazing experiment (PBG) managed with rotational fire. Habitat conditions were significantly different among treatments, and a principal components analysis showed that the patch-burn grazing treatment had higher canopy cover of forbs and habitat heterogeneity than our two control units. To sample the small mammal community, we conducted monthly live trapping of small mammals on two randomly located trap grids in each of our two controls and three units of our PBG treatment. Small mammal diversity was significantly higher in the patch-burn grazing treatment and in the positive control, vs. the negative control. Moreover, a canonical correspondence analysis showed that a fire-grazing interaction was the major driver structuring small mammal communities. Patch-burn grazing is an effective strategy for restoring heterogeneity to vegetative structure and composition, and can increase biodiversity of small mammals in managed rangelands in the tallgrass prairie ecosystem.

Patterns and ecological consequences of water uptake, redistribution, and loss in tallgrass prairie - O'Keefe, Kimberly (Kansas State University, 2016)
Water availability is a key driver of many plant and ecosystem processes in tallgrass prairies, yet we have a limited understanding of how grassland plants utilize water through space and time. Considering that tallgrass prairies experience tremendous heterogeneity in soil resources, identifying spatiotemporal variation in plant ecohydrology is critical for understanding current drivers of plant responses to water and for predicting ecosystem responses to future changes in climate. Here, I investigated the patterns, drivers, and ecological consequences of plant water use (e.g., water uptake, water redistribution, and water loss) in a native tallgrass prairie located in northeastern Kansas, USA. Using a combination of leaf gas exchange, sap flow, and isotopic techniques, I addressed four main questions: 1) How does fire and grazing by bison impact use of water from different sources and niche overlap for common grasses, forbs, and shrubs? 2) Does hydraulic lift occur in grazed and ungrazed tallgrass prairie, and does this impact facilitation for water within grassland communities? 3) What are the patterns and drivers of nocturnal transpiration in common grassland species? 4) How does diel stem sap flow and canopy transpiration vary among common grassland species? I found that bison grazing increased the depth of water uptake by Andropogon gerardii and Rhus glabra, reducing niche overlap with co-occurring species. Conversely, grazing did not affect hydraulic lift, which was generally uncommon and likely limited by nocturnal transpiration. Further, leaf gas exchange measurements indicated that nocturnal transpiration occurred commonly in tallgrass prairie plants and was greatest among grasses and early in the growing season. Nocturnal transpiration was not driven by vapor pressure deficit or soil moisture, as commonly observed in other systems, but was regulated by nocturnal stomatal conductance in most species. Finally, I found that daytime sap flow rates were variable among species and functional types, with larger flux rates among woody species. Nocturnal sap flow rates were more consistent across species, which caused nighttime sap flow and transpiration to account for a larger proportion of daily flux rates in grasses than in forbs or shrubs. These results show that water uptake, water redistribution, and water loss are all influenced by different biotic and abiotic drivers and have varying ecological impacts across a heterogeneous landscape. Additionally, extensive differences in water flux exist among co-occurring species and plant functional groups, which likely reflect varying strategies to tolerate water limitation. These results suggest that shifts in the abundance of these species with future climate changes, or with ecosystem state changes, will likely impact ecosystem-level water balance.
Keywords: Grasslands; Isotopes; Plant physiology; Sap flow; Transpiration

Productivity of North American grasslands is increased under future climate scenarios despite rising aridity - Hufkens, K.; Keenan, T.F.; Flanagan, L.B.; Scott, R.L.; Bernacchi, C.J.; Joo, E.; N. Brunsell; Verfaillie, J.; Richardson, A.D. (Nature Climate Change, 2016)
Grassland productivity is regulated by both temperature and the amount and timing of precipitation1, 2. Future climate change is therefore expected to influence grassland phenology and growth, with consequences for ecosystems and economies. However, the interacting effects of major shifts in temperature and precipitation on grasslands remain poorly understood and existing modelling approaches, although typically complex, do not extrapolate or generalize well and tend to disagree under future scenarios3, 4. Here we explore the potential responses of North American grasslands to climate change using a new, data-informed vegetation–hydrological model, a network of high-frequency ground observations across a wide range of grassland ecosystems and CMIP5 climate projections. Our results suggest widespread and consistent increases in vegetation fractional cover for the current range of grassland ecosystems throughout most of North America, despite the increase in aridity projected across most of our study area. Our analysis indicates a likely future shift of vegetation growth towards both earlier spring emergence and delayed autumn senescence, which would compensate for drought-induced reductions in summer fractional cover and productivity. However, because our model does not include the effects of rising atmospheric CO2 on photosynthesis and water use efficiency5, 6, climate change impacts on grassland productivity may be even larger than our results suggest. Increases in the productivity of North American grasslands over this coming century have implications for agriculture, carbon cycling and vegetation feedbacks to the atmosphere.

Quantifying global soil carbon losses in response to warming - Crowther, T. W.; Todd-Brown, K. E. O.; Rowe, C. W.; Wieder, W. R.; Carey, J. C.; Machmuller, M. B.; Snoek, B. L.; Fang, S.; Zhou, G.; Allison, S. D.; John M. Blair; Bridgham, S. D.; et al. (Nature, 2016)
The majority of the Earth’s terrestrial carbon is stored in the soil. If anthropogenic warming stimulates the loss of this carbon to the atmosphere, it could drive further planetary warming, Despite evidence that warming enhances carbon fluxes to and from the soil, the net global balance between these responses remains uncertain. Here we present a comprehensive analysis of warming-induced changes in soil carbon stocks by assembling data from 49 field experiments located across North America, Europe and Asia. We find that the effects of warming are contingent on the size of the initial soil carbon stock, with considerable losses occurring in high-latitude areas. By extrapolating this empirical relationship to the global scale, we provide estimates of soil carbon sensitivity to warming that may help to constrain Earth system model projections. Our empirical relationship suggests that global soil carbon stocks in the upper soil horizons will fall by 30 ± 30 petagrams of carbon to 203 ± 161 petagrams of carbon under one degree of warming, depending on the rate at which the effects of warming are realized. Under the conservative assumption that the response of soil carbon to warming occurs within a year, a business-as-usual climate scenario would drive the loss of 55 ± 50 petagrams of carbon from the upper soil horizons by 2050. This value is around 12–17 per cent of the expected anthropogenic emissions over this period. Despite the considerable uncertainty in our estimates, the direction of the global soil carbon response is consistent across all scenarios. This provides strong empirical support for the idea that rising temperatures will stimulate the net loss of soil carbon to the atmosphere, driving a positive land carbon–climate feedback that could accelerate climate change.
Keywords: Biogeochemistry; carbon cycle

Rangeland responses to predicted increases in drought extremity - Breshears, D.D.; Alan K. Knapp; Law, D.J.; M.D. Smith; Twidwell, D.; Wonkka, C.L. (Rangelands, 2016)
Keywords: Drought; grassland; savanna; shrubland; state and transition; woodland

Relatedness constrains virulence in an obligate avian brood parasite - Rivers, J.W.; Peer, B.D. (Ornithological Science, 2016)
Virulence, the amount of harm a parasite inflicts on its host, is integral to elucidating the evolution of obligate avian brood parasitism. However, we lack information regarding how relatedness is linked to changes in behavior and the degree of harm that brood parasites cause to their hosts (i.e., virulence). The kin competition hypothesis combines theory from offspring signaling and parasite virulence models and states that the begging intensity of co-infecting parasites is driven by their relatedness, with concomitant changes in the degree of virulence expressed by parasitic young. We tested this hypothesis using the Brown-headed Cowbird Molothrus ater, an obligate brood parasitic bird whose virulence at the nestling stage is mediated by vigorous begging displays that are used to outcompete host young during feeding bouts. We found support for both predictions of the kin competition hypothesis: first, the begging intensity of cowbirds was greater in a population where cowbirds typically competed against unrelated host nestmates, relative to a population where they often competed against kin. Second, the greater intensity of begging in cowbirds was positively associated with decreased growth in host offspring during the developmental period. Given the dearth of studies on virulence in avian brood parasites, our results notably extend our understanding of how relatedness is linked to parasite behavior and virulence, and they highlight how spatially-isolated host populations can harbor different levels of virulence that are driven by competitive interactions between co-infecting parasites.
Keywords: begging; brown-headed cowbird; Kin competition hypothesis; Molothrus ater; Virulence

A safety vs efficiency trade-off identified in the hydraulic pathway of grass leaves is decoupled from photosynthesis, stomatal conductance and precipitation - Ocheltree, Troy W.; Jesse B. Nippert; Prasad, P. V. Vara (New Phytologist, 2016)
A common theme in plant physiological research is the trade-off between stress tolerance and growth; an example of this trade-off at the tissue level is the safety vs efficiency hypothesis, which suggests that plants with the greatest resistance to hydraulic failure should have low maximum hydraulic conductance. Here, we quantified the leaf-level drought tolerance of nine C4 grasses as the leaf water potential at which plants lost 50% (P50 × RR ) of maximum leaf hydraulic conductance (Ksat ), and compared this trait with other leaf-level and whole-plant functions. We found a clear trade-off between Ksat and P50 × RR when Ksat was normalized by leaf area and mass (P = 0.05 and 0.01, respectively). However, no trade-off existed between P50 × RR and gas-exchange rates; rather, there was a positive relationship between P50 × RR and photosynthesis (P = 0.08). P50 × RR was not correlated with species distributions based on precipitation (P = 0.70), but was correlated with temperature during the wettest quarter of the year (P < 0.01). These results suggest a trade-off between safety and efficiency in the hydraulic system of grass leaves, which can be decoupled from other leaf-level functions. The unique physiology of C4 plants and adaptations to pulse-driven systems may provide mechanisms that could decouple hydraulic conductance from other plant functions.

The sensitivity of carbon exchanges in Great Plains grasslands to precipitation variability - Petrie, M.D.; N. Brunsell; Vargas, R.; Scott. L. Collins; Flanagan, L.B.; Hanan, N.P.; Litvak, M.E.; Suyker, A.E. (Journal of Geophysical Research: Biogeosciences, 2016)
In the Great Plains, grassland carbon dynamics differ across broad gradients of precipitation and temperature, yet finer-scale variation in these variables may also affect grassland processes. Despite the importance of grasslands, there is little information on how fine-scale relationships compare between them regionally. We compared grassland C exchanges, energy partitioning and precipitation variability in eight sites in the eastern and western Great Plains using eddy covariance and meteorological data. During our study, both eastern and western grasslands varied between an average net carbon sink and a net source. Eastern grasslands had a moderate vapor pressure deficit (VPD = 0.95 kPa) and high growing season gross primary productivity (GPP = 1010 ± 218 g C m−2 m−2 y−1). Western grasslands had a growing season with higher VPD (1.43 kPa) and lower GPP (360 ± 127 g C m−2 m−2 y−1). Western grasslands were sensitive to precipitation at daily timescales, whereas eastern grasslands were sensitive at monthly and seasonal timescales. Our results support the expectation that C exchanges in these grasslands differ as a result of varying precipitation regimes. Because eastern grasslands are less influenced by short-term variability in rainfall than western grasslands, the effects of precipitation change are likely to be more predictable in eastern grasslands because the timescales of variability that must be resolved are relatively longer. We postulate increasing regional heterogeneity in grassland C exchanges in the Great Plains in coming decades.

Shared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands - M.D. Smith; Alan K. Knapp; Scott. L. Collins; Burkepile, D.E.; Kirkman, K.P.; Koerner, S.E.; Thompson, D.I.; John M. Blair; Burns, C.E.; Eby, S.; Forrestel, E.J.; Fynn, R.W.S.; et al. (BioScience, 2016)
Fire and grazing, key determinants of structure and function of savanna grasslands worldwide, have been extensively altered by humans. We used existing long-term manipulations of fire and grazing in North American and South African mesic savanna grasslands, as well as new experiments, to determine whether the impacts of fire and grazing by large herbivores differed between these systems. We found that despite a body of literature suggesting that these savanna grasslands respond uniquely to fire and grazing, their ecosystem responses (aboveground productivity) were generally similar. In contrast, plant-community responses to fire and herbivores diverged strongly between systems. The differences in plant-community responses, as well as convergence in ecosystem function, were underpinned by a common mechanism: the response of grass dominance to changing fire and grazing regimes. As a result, divergent responses of plant communities to altered fire and grazing regimes did not preclude convergence in ecosystem function.
Keywords: Aboveground net primary productivity; fire; grassland; Grazing; plant community

Shrews and their parasites: small species indicate big changes - Hope, A.G.; Greiman, S.E.; Tkach, V.V.; Hoberg, E.P.; Cook, J.A. (NOAA Arctic Report Card, 2016)
As Arctic climate warms, how will terrestrial ecosystems and interconnected communities respond in the coming decades? Small mammals, such as shrews, and their parasites can serve as key indicators for anticipating the consequences of accelerating environmental perturbation and changing interactions among species. Some Arctic shrews have recently acquired new parasites indicating poleward shifts of sub-Arctic faunas, and demonstrating increases in both Arctic biodiversity and overall complexity within these novel species networks. Spatially broad and temporally deep specimen collections of small mammals and parasites are revealing the extent and nature of community reorganization as northern faunas adjust to accelerating climate change.

Soil characteristics and ecosystem-level effects of woody species encroachment in tallgrass prairie - Mino, L.A. (Oklahoma State University, 2016)

Soil nutrient additions increase invertebrate herbivore abundances, but not herbivory, across three grassland systems - Kimberly J. La Pierre; M.D. Smith (Oecologia, 2016)
Resource availability may influence invertebrate communities, with important consequences for ecosystem function, such as biomass production. We assessed: (1) the effects of experimental soil nutrient additions on invertebrate abundances and feeding rates and (2) the resultant changes in the effects of invertebrates on aboveground plant biomass at three grassland sites spanning the North American Central Plains, across which plant tissue chemistry and biomass vary. Invertebrate communities and rates of herbivory were sampled within a long-term nutrient-addition experiment established at each site along the broad Central Plains precipitation gradient. Additionally, the effects of invertebrates on aboveground plant biomass were determined under ambient and elevated nutrient conditions. At the more mesic sites, invertebrate herbivore abundances increased and their per capita rate of herbivory decreased with nutrient additions. In contrast, at the semi-arid site where plant biomass is low and plant nutrient concentrations are high, invertebrate herbivore abundances did not vary and per capita rates of herbivory increased with nutrient additions. No change in the effect of invertebrate herbivores on aboveground plant biomass was observed at any of the sites. In sum, nutrient additions induced shifts in both plant biomass and leaf nutrient content, which altered invertebrate abundances and feeding rate. However, due to the inverse relationship between changes in herbivore abundance and per capita rates of herbivory, nutrient additions did not alter the effect of invertebrates on aboveground biomass. Overall, we suggest that this inverse response of herbivore abundance and per capita feeding rate may buffer ecosystems against changes in invertebrate damage in response to fluctuations in nutrient levels.
Keywords: Central Plains; nitrogen; Per capita herbivory rate; Phosphorus; Plant tissue chemistry

Spatial and successional dynamics of microbial biofilm communities in a grassland stream ecosystem - Veach, A.M.; Stagen, J.C.; Brown, S.P.; W. K. Dodds; A. Jumpponen (Molecular Ecology, 2016)
Biofilms represent a metabolically active and structurally complex component of freshwater ecosystems. Ephemeral prairie streams are hydrologically harsh and prone to frequent perturbation. Elucidating both functional and structural community changes over time within prairie streams provides a general understanding of microbial responses to environmental disturbance. We examined microbial succession of biofilm communities at three sites in a third-order stream at Konza Prairie over a 2- to 64-day period. Microbial abundance (bacterial abundance, chlorophyll a concentrations) increased and never plateaued during the experiment. Net primary productivity (net balance of oxygen consumption and production) of the developing biofilms did not differ statistically from zero until 64 days suggesting a balance of the use of autochthonous and allochthonous energy sources until late succession. Bacterial communities (MiSeq analyses of the V4 region of 16S rRNA) established quickly. Bacterial richness, diversity and evenness were high after 2 days and increased over time. Several dominant bacterial phyla (Beta-, Alphaproteobacteria, Bacteroidetes, Gemmatimonadetes, Acidobacteria, Chloroflexi) and genera (Luteolibacter, Flavobacterium, Gemmatimonas, Hydrogenophaga) differed in relative abundance over space and time. Bacterial community composition differed across both space and successional time. Pairwise comparisons of phylogenetic turnover in bacterial community composition indicated that early-stage succession (≤16 days) was driven by stochastic processes, whereas later stages were driven by deterministic selection regardless of site. Our data suggest that microbial biofilms predictably develop both functionally and structurally indicating distinct successional trajectories of bacterial communities in this ecosystem.

Stability of grassland soil C and N pools despite 25 years of an extreme climatic and disturbance regime - K.R. Wilcox; John M. Blair; Alan K. Knapp (Journal of Geophysical Research: Biogeosciences, 2016)
Global changes are altering many important drivers of ecosystem functioning, with precipitation amount and disturbance frequency being especially important. Carbon (C) and nitrogen (N) pools are key contemporary attributes of ecosystems that can also influence future C uptake via plant growth. Thus, understanding the impacts of altered precipitation amounts (through controls of primary production inputs) and disturbance regimes (through losses of C and N in biomass) is important to project how ecosystem services will respond to future global changes. A major difficulty inherent within this task is that drivers of ecosystem function and processes often interact, resulting in novel ecosystem responses. To examine how changes in precipitation affect grassland ecosystem responses under a frequent disturbance regime (annual fire), we assessed the biogeochemical and ecological consequences of more than two decades of irrigation in an annually burned mesic grassland in the central United States. In this experiment, precipitation amount was increased by 31% relative to ambient and 1 in 3 years were statistically extreme relative to the long-term historical record. Despite evidence that irrigation decreased root:shoot ratios and increased rates of N cycling—each expected to reduce soil C and N with annual burning—we detected no changes in these biogeochemical pools. This surprising biogeochemical resistance highlights the need to explore additional mechanisms within long-term experiments concerning the consequences of global change impacts on ecosystems.

Stream CO2 degassing: review of methods and laboratory validation of floating chambers - Rawitch, M. J. (University of Kansas, 2016)

Tardigrades of the tree canopy: milnesium swansoni sp.nov. (Eutardigrada: Apochela: Milnesiidae) a new species from Kansas, U.S.A. - Young, A; Chappell, B; Miller, W; Lowman, M (Zootaxa, 2016)
Milnesium swansoni sp. nov. is a new species of Eutardigrada described from the tree canopy in eastern Kansas, USA. This species within the order Apochela, family Milnesiidae, genus Milnesium is distinguished by its smooth cuticle, narrow buccal tube, four peribuccal lamellae, primary claws without accessory points, and a secondary claw configuration of [3-3]-[3-3]. The buccal tube appears to be only half the width of the nominal species Milnesium tardigradum for animals of similar body length. The species adds to the available data for the phylum, and raises questions concerning species distribution.
Keywords: Canopy diversity; Four peribuccal lamellae; Tardigrada; Thorpe morphometry

A thermodynamic approach for assessing agroecosystem sustainability - Cochran, F. V.; N. Brunsell; Sukyer, A. (Ecological Indicators, 2016)
By revisiting theoretical concepts in biogeography and the importance of thermodynamic laws in biosphere-atmosphere interactions, ecological sustainability in agricultural systems may be better deﬁned. In this case study, we employed a multidisciplinary methodology for exploring agroecosystem sustainability by using eddy covariance (EC) data to compute thermodynamic entropy production () and relate it to water, energy and carbon cycling in croplands and grasslands of the Central US. From 2002 to 2012, the biophysical metric of was compared across AmeriFlux sites, each with site-speciﬁc land management practices of irrigation, crop rotation, and tillage. Results show that is most correlated with net ecosystem exchange (NEE) of carbon, and when cropland and grassland sites are close to being carbon neutral, values range from 0.51–1.0 W K−1 m−2 for grasslands, 0.81–1.0 W K−1 m−2 for rainfed croplands, and 0.81–1.1 W K−1 m−2 for irrigated croplands. Irrigated maize stressed by hydrologic and high temperature anomalies associated with the 2012 drought exhibit the greatest increase in , indicating the possibility of decreased sustainability compared to rainfed croplands and grasslands. These results suggest that maximizing carbon uptake with irrigation and fertilizer use tends to move agroecosystems further away from thermodynamic equilibrium, which has implications for ecological sustainability and greenhouse gas (GHG) mitigation in climate-smart agriculture. The underlying theoretical concepts, multidisciplinary methodology, and use of eddy covariance data for biophysical indicators in this study contribute to a unique understanding of ecological sustainability in agricultural systems.

Tight coupling of leaf area index to canopy nitrogen and phosphorus across heterogeneous tallgrass prairie communities - Klodd, A.E.; Jesse B. Nippert; Z. Ratajczak; Waring, H.; Phoenix, G.K. (Oecologia, 2016)
Nitrogen (N) and phosphorus (P) are limiting nutrients for many plant communities worldwide. Foliar N and P along with leaf area are among the most important controls on photosynthesis and hence productivity. However, foliar N and P are typically assessed as species level traits, whereas productivity is often measured at the community scale. Here, we compared the community-level traits of leaf area index (LAI) to total foliar nitrogen (TFN) and total foliar phosphorus (TFP) across nearly three orders of magnitude LAI in grazed and ungrazed tallgrass prairie in north-eastern Kansas, USA. LAI was strongly correlated with both TFN and TFP across communities, and also within plant functional types (grass, forb, woody, and sedge) and grazing treatments (bison or cattle, and ungrazed). Across almost the entire range of LAI values and contrasting communities, TFN:TFP ratios indicated co-limitation by N and P in almost all communities; this may further indicate a community scale trend of an optimal N and P allocation per unit leaf area for growth. Previously, results from the arctic showed similar tight relationships between LAI:TFN, suggesting N is supplied to canopies to maximize photosynthesis per unit leaf area. This tight coupling between LAI, N, and P in tallgrass prairie suggests a process of optimal allocation of N and P, wherein LAI remains similarly constrained by N and P despite differences in species composition, grazing, and canopy density.
Keywords: Co-limitation; fire; grassland; grazers; nutrients

Vocal matching and intensity of begging calls are associated with a forebrain song circuit in a generalist brood parasite - Liu, W.C.; Rivers, J.W.; White, D.J. (Developmental Neurobiology, 2016)
Vocalizations produced by developing young early in life have simple acoustic features and are thought to be innate. Complex forms of early vocal learning are less likely to evolve in young altricial songbirds because the forebrain vocal-learning circuit is underdeveloped during the period when early vocalizations are produced. However, selective pressure experienced in early postnatal life may lead to early vocal learning that is likely controlled by a simpler brain circuit. We found the food begging calls produced by fledglings of the brown-headed cowbird (Molothrus ater), a generalist avian brood parasite, induced the expression of several immediate early genes and early circuit innervation in a forebrain vocal-motor pathway that is later used for vocal imitation. The forebrain neural activity was correlated with vocal intensity and variability of begging calls that appears to allow cowbirds to vocally match host nestmates. The begging-induced forebrain circuits we observed in fledgling cowbirds were not detected in nonparasitic passerines, including species that are close relatives to the cowbird. The involvement of forebrain vocal circuits during fledgling begging and its association with vocal learning plasticity may be an adaptation that provides young generalist brood parasites with a flexible signaling strategy to procure food from a wide range of heterospecific host parents.
Keywords: brood parasitism; brown-headed cowbird; food begging call; parental care; vocal learning

Warm spring reduced carbon cycle impact of the 2012 US summer drought - Wolf, S.; Keenan, T.F.; Fisher, J.B.; Baldocchi, D.D.; Desai, A.R.; Richardson, A.D.; Scott, R.L.; Law, B.E.; Litvak, M.E.; N. Brunsell; Peters, W.; van der Laan-Luijkx, I.T. (Proceedings of the National Academy of Sciences, 2016)
The global terrestrial carbon sink offsets one-third of the world’s fossil fuel emissions, but the strength of this sink is highly sensitive to large-scale extreme events. In 2012, the contiguous United States experienced exceptionally warm temperatures and the most severe drought since the Dust Bowl era of the 1930s, resulting in substantial economic damage. It is crucial to understand the dynamics of such events because warmer temperatures and a higher prevalence of drought are projected in a changing climate. Here, we combine an extensive network of direct ecosystem flux measurements with satellite remote sensing and atmospheric inverse modeling to quantify the impact of the warmer spring and summer drought on biosphere-atmosphere carbon and water exchange in 2012. We consistently find that earlier vegetation activity increased spring carbon uptake and compensated for the reduced uptake during the summer drought, which mitigated the impact on net annual carbon uptake. The early phenological development in the Eastern Temperate Forests played a major role for the continental-scale carbon balance in 2012. The warm spring also depleted soil water resources earlier, and thus exacerbated water limitations during summer. Our results show that the detrimental effects of severe summer drought on ecosystem carbon storage can be mitigated by warming-induced increases in spring carbon uptake. However, the results also suggest that the positive carbon cycle effect of warm spring enhances water limitations and can increase summer heating through biosphere–atmosphere feedbacks.
Keywords: biosphere–atmosphere feedbacks; carbon uptake; ecosystem fluxes; Eddy covariance; seasonal climate anomalies

Annual burning of a tallgrass prairie inhibits C and N cycling in soil, increasing recalcitrant pyrogenic organic matter storage while reducing N availability - Soong, J.L.; Cotrufo, M.F. (Global Change Biology, 2015)
Grassland ecosystems store an estimated 30% of the world's total soil C and are frequently disturbed by wildfires or fire management. Aboveground litter decomposition is one of the main processes that form soil organic matter (SOM). However, during a fire biomass is removed or partially combusted and litter inputs to the soil are substituted with inputs of pyrogenic organic matter (py-OM). Py-OM accounts for a more recalcitrant plant input to SOM than fresh litter, and the historical frequency of burning may alter C and N retention of both fresh litter and py-OM inputs to the soil. We compared the fate of these two forms of plant material by incubating 13C- and 15N-labeled Andropogon gerardii litter and py-OM at both an annually burned and an infrequently burned tallgrass prairie site for 11 months. We traced litter and py-OM C and N into uncomplexed and organo-mineral SOM fractions and CO2 fluxes and determined how fire history affects the fate of these two forms of aboveground biomass. Evidence from CO2 fluxes and SOM C:N ratios indicates that the litter was microbially transformed during decomposition while, besides an initial labile fraction, py-OM added to SOM largely untransformed by soil microbes. Additionally, at the N-limited annually burned site, litter N was tightly conserved. Together, these results demonstrate how, although py-OM may contribute to C and N sequestration in the soil due to its resistance to microbial degradation, a long history of annual removal of fresh litter and input of py-OM infers N limitation due to the inhibition of microbial decomposition of aboveground plant inputs to the soil. These results provide new insight into how fire may impact plant inputs to the soil, and the effects of py-OM on SOM formation and ecosystem C and N cycling.
Keywords: tallgrass prairie

Anthropogenic nitrogen deposition predicts local grassland primary production worldwide - Stevens, C.J.; Lind, E.M.; Hautier, Y.; Harpole, W.S.; E.T. Borer; Hobbie, S.; Seabloom, E.Q.; L. Ladwig; J.D. Bakker; Chu, C.; Scott. L. Collins; Davies, K.F.; et al. (Ecology, 2015)
Humans dominate many important Earth system processes including the nitrogen (N) cycle. Atmospheric N deposition affects fundamental processes such as carbon cycling, climate regulation, and biodiversity, and could result in changes to fundamental Earth system processes such as primary production. Both modelling and experimentation have suggested a role for anthropogenically altered N deposition in increasing productivity, nevertheless, current understanding of the relative strength of N deposition with respect to other controls on production such as edaphic conditions and climate is limited. Here we use an international multiscale data set to show that atmospheric N deposition is positively correlated to aboveground net primary production (ANPP) observed at the 1-m2 level across a wide range of herbaceous ecosystems. N deposition was a better predictor than climatic drivers and local soil conditions, explaining 16% of observed variation in ANPP globally with an increase of 1 kg N·ha−1·yr−1 increasing ANPP by 3%. Soil pH explained 8% of observed variation in ANPP while climatic drivers showed no significant relationship. Our results illustrate that the incorporation of global N deposition patterns in Earth system models are likely to substantially improve estimates of primary production in herbaceous systems. In herbaceous systems across the world, humans appear to be partially driving local ANPP through impacts on the N cycle.

Assessing grassland sensitivity to global change - K.R. Wilcox (Colorado State University, 2015)

Belowground bud bank response to grazing under severe, short-term drought - VanderWeide, B.L.; D.C. Hartnett (Oecologia, 2015)
While the effects of drought and grazing are often studied separately, these disturbances co-occur in grasslands worldwide and interactively influence population, community, and ecosystem processes. The effects of drought and grazing on the belowground bud bank may dictate the trajectory of community recovery because new shoots arise from belowground buds after disturbance in perennial grasslands. We therefore investigated the separate and interactive effects of severe drought and grazing on the belowground bud bank and aboveground vegetation in the tallgrass prairie of northeast Kansas, USA. Contrary to our expectations, we observed changes in community structure and declines in species richness both above and below ground in response to drought and grazing. We also hypothesized that drought would reduce bud bank density of all taxonomic groups, but found that grass bud and shoot densities remained constant across all drought and grazing treatment combinations. While sedge and forb bud and shoot densities were reduced by drought, only sedge bud density declined to a greater extent when grazed under drought conditions. Live rhizome biomass did not vary by treatment and was highly correlated with bud bank density, suggesting that bud demography is tightly linked to the production and senescence of rhizomes. Despite the effects of drought and grazing on aboveground net primary productivity and community structure, our work suggests that grasses stabilize tallgrass prairie plant communities because their rhizomes and associated buds persist through co-occurring disturbances.
Keywords: Climate change; Ecological stability; Herbivory; tallgrass prairie; water stress

Biogeographic influences on grassland community structure and function - Forrestel, Elisabeth.J. (Yale University, 2015)

Biophysical controls on carbon and water vapor fluxes across a grassland climatic gradient in the United States - Wagle, Pradeep; Xiao, Xiangming; Scott, Russell L.; Kolb, Thomas E.; Cook, David R.; N. Brunsell; Baldocchi, Dennis D.; Basara, Jeffrey; Matamala, Roser; Zhou, Yuting; Bajgain, Rajen (Agricultural and Forest Meteorology, 2015)
Understanding of the underlying causes of spatial variation in exchange of carbon and water vapor fluxes between grasslands and the atmosphere is crucial for accurate estimates of regional and global carbon and water budgets, and for predicting the impact of climate change on biosphere–atmosphere feedbacks of grasslands. We used ground-based eddy flux and meteorological data, and the Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) from 12 grasslands across the United States to examine the spatial variability in carbon and water vapor fluxes and to evaluate the biophysical controls on the spatial patterns of fluxes. Precipitation was strongly associated with spatial and temporal variability in carbon and water vapor fluxes and vegetation productivity. Grasslands with annual average precipitation <600 mm generally had neutral annual carbon balance or emitted small amount of carbon to the atmosphere. Despite strong coupling between gross primary production (GPP) and evapotranspiration (ET) across study sites, GPP showed larger spatial variation than ET, and EVI had a greater effect on GPP than on ET. Consequently, large spatial variation in ecosystem water use efficiency (EWUE = annual GPP/ET; varying from 0.67 ± 0.55 to 2.52 ± 0.52 g C mm−1 ET) was observed. Greater reduction in GPP than ET at high air temperature and vapor pressure deficit caused a reduction in EWUE in dry years, indicating a response which is opposite than what has been reported for forests. Our results show that spatial and temporal variations in ecosystem carbon uptake, ET, and water use efficiency of grasslands were strongly associated with canopy greenness and coverage, as indicated by EVI.
Keywords: Ecosystem water use efficiency; Eddy covariance; Enhanced vegetation index; Evapotranspiration; Grasslands; Gross primary production

Bison foraging responds to fire frequency in nutritionally heterogeneous grassland - Raynor, E.J.; Anthony Joern; J. M. Briggs (Ecology, 2015)
Foraging decisions by native grazers in fire-dependent landscapes modulate the fire–grazing interaction. Uncovering the behavioral mechanisms associated with the attraction of grazers to recently burned areas requires understanding at multiple spatial scales in the ecological foraging hierarchy. This study focused on feeding in the area between steps in a foraging bout, the feeding station, as forage chemistry and vegetation architecture play central roles in these fine-scale, feeding-station decisions. The forage maturation hypothesis (FMH) uses the temporal dynamics of forage quality and quantity in grasslands to explain the distribution of large herbivores, but does not address herbivore responses to inter-patch variation caused by fire-induced nutrient increases of forage quality. Using an experimental setting with contrasting fire treatments we describe the effects of variable burn history on foraging kinetics by bison at Konza Prairie Biological Station (KPBS). We assessed the potential to link the FMH in a complementary fashion to the transient maxima hypothesis (TMH) to explain temporal variation in bison responses to grassland forage quality and quantity in response to burning at different temporal frequencies. Forage attributes met predictions of the TMH that allowed us to investigate how forage maturation affects feeding station foraging behavior across watersheds with varying burn frequency. At sites burned in the spring after several years without burning, both bite mass and intake rate increased with increasing biomass at a greater rate during the growing season than during the transitional midsummer seasonal period. In these infrequently burned watersheds, early growing season bite mass (0.6 ± 0.05 g; mean ± SE), bite rate (38 ± 1.5 bites/min), and intake rate (21 ± 2.3 g/min) was reduced by ~15%, 13%, and 29% during the midsummer transitional period. A behavioral response in foraging kinetics at the feeding station occurred where a nonequilibrial pulse of high-quality resource was made available and then retained by repeated grazing over the growing season. Our results provide the first experimental evidence for demonstrating the fine-scale behavioral response of a large grazer to fire-induced changes in forage attributes, while linking two prominent hypotheses proposed to explain spatial variation in forage quality and quantity at local and landscape scales.

Booming from the mists of nowhere: the story of the Greater Prairie Chicken - Hoch, Greg (University of Iowa Press, 2015)

Breeding system and sex ratio variation in mulberries - Nepal, M.P.; Ferguson, C.J.; Mayfield, M.H. (Journal of the Botanical Research Institute of Texas, 2015)
Flowering plants exhibit a diverse array of sex expression patterns that become of particular interest when considered in the context of coexisting native-invasive congeners. This study presents findings on sex expression and sex ratio variation in two congeneric tree species, the native Morus rubra and the exotic M. alba, in the Flint Hills region of the Great Plains in the United States. Both species exhibited a subdioecious breeding system (with male, female and hermaphrodite individuals co-occurring within populations), and significantly male-biased sex ratios (i.e., males are more numerous than females). Cumulative sex ratio deviation was higher in the native M. rubra populations than in the exotic M. alba. Within-species sex ratio did not vary significantly among populations. In one focus study area surveyed over three years, most individuals were consistent in sex expression, but approximately 10% switched their sex at least once; the vast majority of these changes were between unisexual and hermaphrodite morphs. There was no size dependence of sex expression based on current sampling. Our results document subdioecy as the breeding system in these Morus species, and advance the group as an interesting study system for its reproductive biology.
Keywords: Breeding system; Moraceae; Morus; sex ratio; sex switch; subdioecy

Bud bank dynamics and clonal growth strategy in the rhizomatous grass Pascopyrum smithii - Ott, J.P.; D.C. Hartnett (Plant Ecology, 2015)
Recruitment of rhizomatous perennial grass ramets primarily occurs from the belowground bud bank. Investment in guerilla versus phalanx growth is determined by bud availability, development, and spatial distribution. The tiller and bud bank dynamics of Pascopyrum smithii, a dominant rhizomatous grass of the northern mixed-grass prairie, were examined in South Dakota throughout an annual cycle to assess the investment in guerilla versus phalanx growth and the role of different bud populations in renewal versus regenerative functions and vegetative spread via rhizomes. Pascopyrum smithii invested substantially in both phalanx and guerilla tiller production. However, investment in rhizome production before tiller recruitment prioritized guerilla over phalanx growth. Annual tiller recruitment of P. smithii was capable of flexible timing, occurring in either spring or fall. Renewal buds, from which rhizomes and tillers were recruited, primarily consisted of the youngest generation of buds borne at the base of tillers. Although rhizome axillary buds and older tiller axillary buds were rarely used in annual tiller recruitment, they provided a sizable reserve (regenerative) bud bank. The spatial distribution of bud development produced the mixed guerrilla–phalanx growth pattern and flexible tiller recruitment timing of P. smithii. Therefore, P. smithii is capable of employing both conservative and foraging growth strategies which will facilitate its persistence under local neighborhood variability and changing resource availability associated with environmental change. Understanding the spatial distribution of buds as determined by rhizome architecture is essential to understanding the distribution and composition of species within plant communities dominated by clonal species.
Keywords: Bud; Guerilla; Phalanx Rhizome; Vegetative reproduction; Western wheatgrass

Challenging the maximum rooting depth paradigm in grasslands and savannas - Jesse B. Nippert; Holdo, R. M. (Functional Ecology, 2015)
For many grassland and savanna ecosystems, water limitation is a key regulator of individual plant, community and ecosystem processes. Maximum rooting depth is commonly used to characterize the susceptibility of plant species to drought. This rests on the assumption that deep-rooted plant species would have a greater total volume of soil water to exploit and should be less susceptible to episodic changes in water availability. Independent of maximum rooting depth, rooting strategies based on differences in biomass allocation with depth, uptake plasticity in relation to water availability and variation in water transport capability may all influence growth responses and susceptibility to drought. Many examples from grasslands and savannas reflect these rooting strategies among coexisting grass, forb and woody species. Here, we use a dynamic model of plant water uptake and growth to show how changes in root distribution, functional plasticity and root hydraulic conductivity have the potential to influence aboveground biomass and competitive outcomes, even when maximum rooting depth remains constant. We also show theoretically that shifts in root distribution to surface soils without changes in maximum depth can potentially outweigh the benefits of increased maximum rooting depth. Combining our current reliance on biogeographic descriptions of maximum rooting depth with insights about other, more subtle aspects of root structure and function are likely to improve our understanding of ecosystem responses to dynamic water limitation.

Characterizing differences in precipitation regimes of extreme wet and dry years: Implications for climate change experiments - Alan K. Knapp; D.L. Hoover; K.R. Wilcox; M.L. Avolio; Koerner, S.E.; Kimberly J. La Pierre; Loik, M.E.; Luo, Y.; Sala, O.E.; M.D. Smith (Global Change Biology, 2015)
Climate change is intensifying the hydrologic cycle and is expected to increase the frequency of extreme wet and dry years. Beyond precipitation amount, extreme wet and dry years may differ in other ways, such as the number of precipitation events, event size, and the time between events. We assessed 1614 long-term (100 year) precipitation records from around the world to identify key attributes of precipitation regimes, besides amount, that distinguish statistically extreme wet from extreme dry years. In general, in regions where mean annual precipitation (MAP) exceeded 1000 mm, precipitation amounts in extreme wet and dry years differed from average years by ~40% and 30%, respectively. The magnitude of these deviations increased to >60% for dry years and to >150% for wet years in arid regions (MAP<500 mm). Extreme wet years were primarily distinguished from average and extreme dry years by the presence of multiple extreme (large) daily precipitation events (events >99th percentile of all events); these occurred twice as often in extreme wet years compared to average years. In contrast, these large precipitation events were rare in extreme dry years. Less important for distinguishing extreme wet from dry years were mean event size and frequency, or the number of dry days between events. However, extreme dry years were distinguished from average years by an increase in the number of dry days between events. These precipitation regime attributes consistently differed between extreme wet and dry years across 12 major terrestrial ecoregions from around the world, from deserts to the tropics. Thus, we recommend that climate change experiments and model simulations incorporate these differences in key precipitation regime attributes, as well as amount into treatments. This will allow experiments to more realistically simulate extreme precipitation years and more accurately assess the ecological consequences.
Keywords: rainfall patterns

Consistent responses of soil microbial communities to elevated nutrient inputs in grasslands across the globe - Leff, J.W.; Jones, S.E.; Prober, S.M.; Barberán, A.; E.T. Borer; Firn, J.L.; Harpole, W.S.; Hobbie, S.E.; Hofmockel, K.S.; Knops, J.M.H.; McCulley, R.L.; Kimberly J. La Pierre; et al. (Proceedings of the National Academy of Sciences, 2015)
Soil microorganisms are critical to ecosystem functioning and the maintenance of soil fertility. However, despite global increases in the inputs of nitrogen (N) and phosphorus (P) to ecosystems due to human activities, we lack a predictive understanding of how microbial communities respond to elevated nutrient inputs across environmental gradients. Here we used high-throughput sequencing of marker genes to elucidate the responses of soil fungal, archaeal, and bacterial communities using an N and P addition experiment replicated at 25 globally distributed grassland sites. We also sequenced metagenomes from a subset of the sites to determine how the functional attributes of bacterial communities change in response to elevated nutrients. Despite strong compositional differences across sites, microbial communities shifted in a consistent manner with N or P additions, and the magnitude of these shifts was related to the magnitude of plant community responses to nutrient inputs. Mycorrhizal fungi and methanogenic archaea decreased in relative abundance with nutrient additions, as did the relative abundances of oligotrophic bacterial taxa. The metagenomic data provided additional evidence for this shift in bacterial life history strategies because nutrient additions decreased the average genome sizes of the bacterial community members and elicited changes in the relative abundances of representative functional genes. Our results suggest that elevated N and P inputs lead to predictable shifts in the taxonomic and functional traits of soil microbial communities, including increases in the relative abundances of faster-growing, copiotrophic bacterial taxa, with these shifts likely to impact belowground ecosystems worldwide.
Keywords: Fertilization; shotgun metagenomics; Soil bacteria; Soil ecology; Soil fungi

Contrasting above- and belowground sensitivity of three Great Plains grasslands to altered rainfall regimes - K.R. Wilcox; Von Fischer, J.C.; Muscha, J.M.; Petersen, M.K.; Alan K. Knapp (Global Change Biology, 2015)
Intensification of the global hydrological cycle with atmospheric warming is expected to increase interannual variation in precipitation amount and the frequency of extreme precipitation events. Although studies in grasslands have shown sensitivity of aboveground net primary productivity (ANPP) to both precipitation amount and event size, we lack equivalent knowledge for responses of belowground net primary productivity (BNPP) and NPP. We conducted a 2-year experiment in three US Great Plains grasslands – the C4-dominated shortgrass prairie (SGP; low ANPP) and tallgrass prairie (TGP; high ANPP), and the C3-dominated northern mixed grass prairie (NMP; intermediate ANPP) – to test three predictions: (i) both ANPP and BNPP responses to increased precipitation amount would vary inversely with mean annual precipitation (MAP) and site productivity; (ii) increased numbers of extreme rainfall events during high-rainfall years would affect high and low MAP sites differently; and (iii) responses belowground would mirror those aboveground. We increased growing season precipitation by as much as 50% by augmenting natural rainfall via (i) many (11–13) small or (ii) fewer (3–5) large watering events, with the latter coinciding with naturally occurring large storms. Both ANPP and BNPP increased with water addition in the two C4 grasslands, with greater ANPP sensitivity in TGP, but greater BNPP and NPP sensitivity in SGP. ANPP and BNPP did not respond to any rainfall manipulations in the C3-dominated NMP. Consistent with previous studies, fewer larger (extreme) rainfall events increased ANPP relative to many small events in SGP, but event size had no effect in TGP. Neither system responded consistently above- and belowground to event size; consequently, total NPP was insensitive to event size. The diversity of responses observed in these three grassland types underscores the challenge of predicting responses relevant to C cycling to forecast changes in precipitation regimes even within relatively homogeneous biomes such as grasslands.

The diet of upland sandpipers (Bartramia longicauda) in managed farmland in their neotropical non-breeding grounds - M. Alfaro-Barrios; Sandercock, B.K.; Liguori, L.; Arim, M. (Ornitología Neotropical, 2015)
The Upland Sandpiper (Bartramia longicauda) is a migratory shorebird that inhabits grasslands at the breeding and non-breeding grounds. The trophic ecology of the species is poorly known, but it is thought to be insectivorous. In this study, we describe the diet of the Upland Sandpiper and its temporal variation in grasslands of northern Uruguay. From 2008 to 2012, we collected 67 feces at nine different sites in the Departments of Salto and Paysandú. The diet consisted mainly of insects (present in 98% of the feces) belonging to three orders: Coleoptera (in 80% of feces), Orthoptera (79%), and Hymenoptera (48%). Consumption of Orthoptera and Hymenoptera varied among years. Plant remains and stones were also recorded in feces. Vegetation may have been consumed secondarily while stones could be used in food processing in the gizzard. Our study demonstrates that Upland Sandpipers are diet generalists and probably forage opportunistically, depending on resource availability and focusing on the most abundant prey items.
Keywords: Bartramia longicauda; diet; fecal analysis; food preference; grasslands; insects; Nearctic migrant; Scolopacidae; Upland Sandpiper; Uruguay; wintering grounds

Differential sensitivity to regional-scale drought in six central US grasslands - Alan K. Knapp; Carroll, C.J.W.; Denton, E.M.; Kimberly J. La Pierre; Scott. L. Collins; M.D. Smith (Oecologia, 2015)
Terrestrial ecosystems often vary dramatically in their responses to drought, but the reasons for this are unclear. With climate change forecasts for more frequent and extensive drought in the future, a more complete understanding of the mechanisms that determine differential ecosystem sensitivity to drought is needed. In 2012, the Central US experienced the fourth largest drought in a century, with a regional-scale 40 % reduction in growing season precipitation affecting ecosystems ranging from desert grassland to mesic tallgrass prairie. This provided an opportunity to assess ecosystem sensitivity to a drought of common magnitude in six native grasslands. We tested the prediction that drought sensitivity is inversely related to mean annual precipitation (MAP) by quantifying reductions in aboveground net primary production (ANPP). Long-term ANPP data available for each site (mean length = 16 years) were used as a baseline for calculating reductions in ANPP, and drought sensitivity was estimated as the reduction in ANPP per millimeter reduction in precipitation. Arid grasslands were the most sensitive to drought, but drought responses and sensitivity varied by more than twofold among the six grasslands, despite all sites experiencing 40 % reductions in growing season precipitation. Although drought sensitivity generally decreased with increasing MAP as predicted, there was evidence that the identity and traits of the dominant species, as well as plant functional diversity, influenced sensitivity. A more comprehensive understanding of the mechanisms leading to differences in drought sensitivity will require multi-site manipulative experiments designed to assess both biotic and abiotic determinants of ecosystem sensitivity.
Keywords: Climate change; Functional diversity; Long-term ecological research; Precipitation; Primary production

Dissolved organic carbon concentration and flux in a grassland stream: spatial and temporal patterns and processes from long-term data - Rüegg, J.; Eichmiller, J.J.; Mladenov, N.; W. K. Dodds (Biogeochemistry, 2015)
Dissolved organic carbon (DOC) in streams is a critical component of the global carbon cycle, but little is known about long-term patterns in DOC concentration and export in grassland streams. Here we present the results of a 15-year dataset collected from multiple sites in the Kings Creek watershed on Konza Prairie, KS, USA. DOC concentrations ranged from 0.15 to 15.97 mg L−1, with a mean of 1.19 mg L−1 (standard deviation 1.01 mg L−1). Sites differed in their DOC concentrations as a function of the year of study and the season. Generally, headwaters had greater DOC concentrations, and DOC decreased downstream. The lowest concentrations were found in a groundwater spring in the watershed. Concentrations showed no trend over the study and were not correlated with discharge. However, annual export (mean: 0.29 kg ha−1 year−1; range: 0.00–9.09 kg ha−1 year−1) was highly correlated with annual runoff, and annual runoff explained over 80 % of the variation in export. Export from Kings Creek was 30 times lower than the literature-reported mean for grasslands and 137 times less than export averaged across all biomes. Neither fire nor bison, two forces that maintain prairies, were statistically related to DOC concentrations. Main drivers of DOC concentrations are likely leaching from terrestrial organic material in soils and the accumulations in dry streambeds during drought periods as well as instream autotrophic production. Downstream declines in DOC concentrations suggest instream processing. Grassland streams probably have modest effects on the global carbon budget due to instream processing and low precipitation. Changes in precipitation may have large effects on carbon export from grassland streams.
Keywords: carbon cycle; Carbon export; long-term study; prairie streams

Dynamics of microbial community structure and function in a tallgrass prairie ecosystem - Veach, A.M. (Kansas State University, 2015)
Due to agricultural practices and urbanization, tallgrass prairie ecosystems have become threatened as < 5% of its historical coverage exists today. The small remainder of praire that does exist is further threatened by the encroachment of woody plant species. Woody plant encroachment may not only alter prairie ecosystem function, but also prairie microbial communities responsible for these functional processes. Further, prairies are high disturbance ecosystems, especially prairie streams which are hydrologically harsh. They support communities that frequently undergo succession due to recurring flood and drought conditions, yet little is known about the response of microbial communities to these disturbances. In my dissertation, I first address the degree of woody vegetation expansion in riparian corridors (parallel to streams) in watersheds with variable fire frequency and grazing. I found that the rate of riparian woody expansion declines with higher fire intervals and is not affected by grazing, but even annual burns may not prevent woody plant expansion in riparian zones from occurring. Second, I quantified the effect of using restorations of riparian corridors, through removal of woody plants, on physical, chemical, and microbial community (bacteria and fungi) dynamics across stream to upslope soils. Removal restoration causes a decrease in NH₄⁺ and soil water content, and causes streams and upslope soils to become similar in fungal community richness unlike forested landscapes. Bacterial communities were minimally impacted by removals, but were highly structured among stream to upslope soils due to multiple environmental gradients (i.e., pH, NO₃⁻, soil moisture). Lastly, I examined the successional development of biofilm-associated microbial communities in a prairie stream from both a functional and structural perspective. I found that biofilm microbes exhibited strong successional trajectories, with communities developing towards net autotrophy and therefore becoming reliant upon in-stream derived carbon. Further, bacterial communities displayed spatial differences, but much stronger temporal patterns in community composition were detected. These studies highlight how woody plant encroachment may influence stream ecosystems in addition to spatiotemporal trends in microbial community assembly.
Keywords: Microbial communities; Woody encroachment; Bacteria; Fungi; Biofilms; Stream

Ecological hierarchy of foraging in a large herbivore: the plains bison perspective in tallgrass prairie - Raynor, E.J. (Kansas State University, 2015)
Foraging decisions by native grazers in fire-dependent landscapes reflect fire-grazing interactions. I assessed behavioral responses associated with the attraction of grazers to recently burned areas at multiple spatial scales. (a) I focused on feeding in the area between steps in a foraging bout – the feeding station – where forage quality and vegetation architecture underlie these fine-scale decisions. The ‘forage maturation hypothesis’ (FMH) predicts the distribution of large herbivores based on the temporal dynamics of forage quality and quantity, but does not address herbivore responses to inter-patch variation caused by fire-induced increases of forage quality. The ‘transient maxima hypothesis’ (TMH) also predicts variable forage quality and quantity, but in response to intermittent disturbance from fire. I described the effects of variable spring burn history to bison foraging and their spatio-temporal distribution at Konza Prairie. Forage attributes met predictions of the TMH to explain how forage maturation affects foraging behavior across watersheds with varying burn frequency. At sites burned in the spring after several years without burning, intake rate increased with increasing vegetation biomass at a greater rate during the early growing season than during the transitional mid-summer period. This foraging behavior occurred in response to a non-equilibrial pulse of high quality resource that set the stage in the burned area, and was then retained by repeated grazing over the growing season. Thus, bison responded increased forage resource availability resulting from transient maxima in infrequently-burned watersheds burned that spring and they intensely used these areas until forage availability and forage regrowth was not possible. (b) At the patch scale, bison selected areas of low-to-moderate grass cover in which to feed and avoided areas of high forb cover in the growing season. During the dormant season, however, bison selected feeding-sites with uniformly high canopy cover in watersheds that were not burned. (c) At the landscape-scale, infrequently burned watersheds (compared to watersheds that were not burned) provided the strongest significant predictor of bison space use in all early growing- and transitional-season months. (d) The probability of habitat selection was driven by availability of high foliar, protein and low-to-intermediate herbaceous biomass throughout the growing season. These results explain the hierarchy of foraging by a dominant consumer in an experimental landscape by linking two prominent hypotheses, TMH-FMH, proposed to explain spatial variation in forage quality and quantity at local and landscape scales.
Keywords: Bison; Foraging Behavior; Forage Maturation; Movement; Space Use; Transient Maxima

Effects of experimental forest removal on macroinvertebrate production and functional structure in tallgrass prairie streams - Vanderymyde, J.M.; M.R. Whiles (Freshwater Science, 2015)
Encroachment by woody vegetation is a major threat to tallgrass prairie streams, and converts them from open- to closed-canopy systems. This change presumably shifts the relative importance of basal resources from autochthonous to allochthonous and may alter functional feeding group composition and production of consumers. Riparian trees were removed from 2 headwater stream reaches on the Konza Prairie Biological Station to examine effects of forest encroachment and removal. Removal reaches were compared to reaches with naturally open and closed canopies before and after manipulation. Benthic organic matter and macroinvertebrates were sampled monthly for 1 y before (year 1) and after (year 2) riparian forest removal. Total secondary production in removal reaches ranged from 8.9 to 10.2 g ash-free dry mass (AFDM) m−2 y−1 in year 1, and increased significantly to 13.4 to 14.5 g AFDM m−2 y−1 in year 2. Scraper production in removal reaches was 2.8 to 3.9 g AFDM m−2 y−1 in year 1, and increased significantly to 6.0 to 8.7 g AFDM m−2 y−1 in year 2. Shredders did not respond negatively to the removal, but scrapers dominated production (45-60% of total) in open and removal reaches after manipulation. Total production in naturally open reaches was 7.6 to 12.6 g AFDM m−2 y−1 in year 1 and decreased to 6.5 to 9.8 g AFDM m−2 y−1 in year 2. Riparian forest removal altered macroinvertebrate production and functional structure, but higher production in removal reaches than in open reaches after manipulation suggested that natural conditions were not restored 1 y after removal. However, ordinations indicated communities in open and removal reaches became more similar after manipulation. Forest encroachment alters prairie stream structure and function, and riparian forest removal may be an effective restoration and management practice for remaining prairie streams.

The effects of genotype richness and genomic dissimilarity of Andropogon gerardii on invasion resistance and productivity - M.L. Avolio; Chang, C.C.; Weis, J.J.; M.D. Smith (Plant Ecology and Diversity, 2015)
Background: The genetic diversity within populations has been shown to affect ecosystem functions, including productivity and invasion resistance. To date most experiments have focused on manipulation of genotypic richness and have ignored other measures of genetic diversity. Aims: In the present study we aimed to establish whether manipulated genotypic richness and genomic dissimilarity of Andropogon gerardii affect productivity and invasion resistance. Methods: We created experimental mesocosms with three levels of genotypic richness: one-, three-, and nine-genotypes. In the three-genotype treatment, we manipulated a range of genomic dissimilarity values (genetic relatedness among individuals). At the end of one growing season we measured above-ground, below-ground and total biomass of the mesocosms, and invasion resistance to Andropogon bladhii. Results: Overall, we found no significant effect of genotypic richness on any measure of ecosystem function, although there tended to be more root biomass (due to complementarity) and invasive seedling biomass with higher levels of genotypic richness. Within the three-genotype treatment we found a significant positive relationship between genomic dissimilarity and above-ground biomass, which was caused by a selection effect. We also found a positive relationship between genomic dissimilarity and biomass of A. bladhii. Conclusions: Using these two measures of genetic diversity we detected differences in the strength and mechanism of positive diversity effects within the same experiment, demonstrating the value of manipulating multiple measures of diversity when performing biodiversity–ecosystem function experiments.
Keywords: Andropogon bladhii; biodiversity ecosystem function; complementarity; dominant species; genomic dissimilarity; genotypic richness; invasion resistance; productivity; tallgrass prairie

Effects of grazing and prescribed fire on resource selection and nest survival of upland sandpipers in an experimental landscape - Sandercock, B.K.; M. Alfaro-Barrios; Casey, A.E.; Johnson, T.N.; Mong, T.W.; Odom, K.J.; Strum, K.M.; Winder, V.L. (Landscape Ecology, 2015)
Context Conservation of grassland vertebrates requires a mechanistic understanding of the effects of landscape heterogeneity on habitat selection and demographic performance. Objectives Our goal was to investigate the effects of rangeland management on resource selection and nest survival of upland sandpipers (Bartramia longicauda). Methods We conducted our project at Konza Prairie, a Long-Term Ecological Research site. The station has 60 experimental units with replicated grazing and fire treatments that create a heterogeneous landscape of different habitat patches. We radio-tracked sandpipers for two breeding seasons (2003–2004, n = 37 birds) and monitored sandpiper nests for eight seasons (2001–2008, n = 246 nests). We used resource utilization functions to examine resource selection with respect to five landscape features. Results Home ranges of sandpipers were large in contiguous prairie (x¯=8.4km2x¯=8.4km2) and explain area-sensitive occurrence in fragmented prairie. Upland sandpipers selected grazed and burned sites with short vegetation within their home range. In contrast, nest site selection was influenced by fire frequency and birds selected infrequently burned sites with greater vegetative structure. Settlement decisions affected fitness because nest survival was low in burned and grazed sites (0.068), but higher in unburned and ungrazed sites (0.201–0.247). Conclusions Our results raise concerns for conservation because private rangelands managed for livestock production are often homogeneous landscapes with heavy grazing and frequent fires. Rotational grazing and fire could be used to restore heterogeneity to grasslands but the duration of rotation, patch size, and optimal configuration require further investigation.
Keywords: Bartramia longicauda; fire; grassland; Habitat selection; Home range; Landscape heterogeneity; Nest survival; Radio-telemetry; Resource utilization functions; tallgrass prairie

Effects of mycorrhizal symbiosis on aboveground arthropod herbivory in tallgrass prairie: an in situ experiment - Kula, A.A.R.; D.C. Hartnett (Plant Ecology, 2015)
Plant–herbivore interactions and mycorrhizal symbiosis are important associations in grasslands that may interact due to their relationships with a common host plant and its resources. However, few studies have explored the effect of mycorrhizal symbiosis on plant–herbivore interactions. An understanding of the complex interactions between host plants, mycorrhizal fungi, and insect herbivores is enhanced by in situ examinations of the three parties acting simultaneously. The objective of this study was to quantify the effects of mycorrhizal symbiosis on insect herbivory and the host-plant community in tallgrass prairie. We used long-term mycorrhizal and fungicide-treated plots at Konza Prairie Biological Station (Manhattan, KS) to determine whether insect herbivory is altered by suppression of mycorrhizal fungi. Herbivory on plants in mycorrhizal control plots was greater than in fungicide-treated plots, and for one plant guild, C3 graminoids, the difference was significant. In fungicide-treated plots, plant diversity was significantly greater and herbivory was negatively correlated with plant species diversity. Differences in productivity of plant functional groups due to mycorrhizal symbiosis may be a key factor in patterns of insect herbivory. The results indicate that mycorrhizal symbiosis has diverse consequences, influencing the abundance and the quality of host plants in tallgrass prairie, as well as their responses to consumers.
Keywords: Arbuscular mycorrhizal fungi; Cool season grass; Forb Mycorrhizal symbiosis; Plant–herbivore interactions; Warm-season grass

Elevated temperatures and drought favor invasive grasses over native species - E.B. Duell (Oklahoma State University, 2015)

Factors affecting female space use in ten populations of prairie chickens - Winder, V.L.; Carrlson, K.M.; Gregory, A.J.; Hagen, C.A.; David A. Haukos; Kesler, D.C.; Larsson, L.C.; Matthews, T.W.; McNew, L.B.; Patten, M.A.; Pitman, J.C.; Powell, L.A.; et al. (Ecosphere, 2015)
Conservation of wildlife depends on an understanding of the interactions between animal movements and key landscape factors. Habitat requirements of wide-ranging species often vary spatially, but quantitative assessment of variation among replicated studies at multiple sites is rare. We investigated patterns of space use for 10 populations of two closely related species of prairie grouse: Greater Prairie-Chickens (Tympanuchus cupido) and Lesser Prairie-Chickens (T. pallidicinctus). Prairie chickens require large, intact tracts of native grasslands, and are umbrella species for conservation of prairie ecosystems in North America. We used resource utilization functions to investigate space use by female prairie chickens during the 6-month breeding season from March through August in relation to lek sites, habitat conditions, and anthropogenic development. Our analysis included data from 382 radio-marked individuals across a major portion of the extant range. Our project is a unique opportunity to study comparative space use of prairie chickens, and we employed standardized methods that facilitated direct comparisons across an ecological gradient of study sites. Median home range size of females varied ~10-fold across 10 sites (3.6–36.7 km2), and home ranges tended to be larger at sites with higher annual precipitation. Proximity to lek sites was a strong and consistent predictor of space use for female prairie chickens at all 10 sites. The relative importance of other predictors of space use varied among sites, indicating that generalized habitat management guidelines may not be appropriate for these two species. Prairie chickens actively selected for prairie habitats, even at sites where ~90% of the land cover within the study area was prairie. A majority of the females monitored in our study (>95%) had activity centers within 5 km of leks, suggesting that conservation efforts can be effectively concentrated near active lek sites. Our data on female space use suggest that lek surveys of male prairie chickens can indirectly assess habitat suitability for females during the breeding season. Lek monitoring and surveys for new leks provide information on population trends, but can also guide management actions aimed at improving nesting and brood-rearing habitats.

Fire history reconstruction in grassland ecosystems: amount of charcoal reflects local area burned - Leys, érangère; Brewer, Simon C; McConaghy, Scott; Mueller, Joshua; McLauchlan, K.K. (Environmental Research Letters, 2015)
Fire is one of the most prevalent disturbances in the Earth system, and its past characteristics can be reconstructed using charcoal particles preserved in depositional environments. Although researchers know that fires produce charcoal particles, interpretation of the quantity or composition of charcoal particles in terms of fire source remains poorly understood. In this study, we used a unique four-year dataset of charcoal deposited in traps from a native tallgrass prairie in mid-North America to test which environmental factors were linked to charcoal measurements on three spatial scales. We investigated small and large charcoal particles commonly used as a proxy of fire activity at different spatial scales, and charcoal morphotypes representing different types of fuel. We found that small (125–250 μm) and large (250 μm–1 mm) particles of charcoal are well-correlated (Spearman correlation = 0.88) and likely reflect the same spatial scale of fire activity in a system with both herbaceous and woody fuels. There was no significant relationship between charcoal pieces and fire parameters <500 m from the traps. Moreover, local area burned (<5 km distance radius from traps) explained the total charcoal amount, and regional burning (200 km radius distance from traps) explained the ratio of non arboreal to total charcoal (NA/T ratio). Charcoal variables, including total charcoal count and NA/T ratio, did not correlate with other fire parameters, vegetation cover, landscape, or climate variables. Thus, in long-term studies that involve fire history reconstructions, total charcoal particles, even of a small size (125–250 μm), could be an indicator of local area burned. Further studies may determine relationships among amount of charcoal recorded, fire intensity, vegetation cover, and climatic parameters.

Formation of soil organic matter via biochemical and physical pathways of litter mass loss - Cotrufo, M.F.; Soong, Jennifer L.; Horton, Andrew J.; Campbell, Eleanor E.; Haddix, L.; Wall, Diana H.; Parton, William J. (Nature Geoscience, 2015)
Soil organic matter is the largest terrestrial carbon pool1. The pool size depends on the balance between formation of soil organic matter from decomposition of plant litter and its mineralization to inorganic carbon. Knowledge of soil organic matter formation remains limited2 and current C numerical models assume that stable soil organic matter is formed primarily from recalcitrant plant litter3. However, labile components of plant litter could also form mineral-stabilized soil organic matter4. Here we followed the decomposition of isotopically labelled above-ground litter and its incorporation into soil organic matter over three years in a grassland in Kansas, USA, and used laboratory incubations to determine the decay rates and pool structure of litter-derived organic matter. Early in decomposition, soil organic matter formed when non-structural compounds were lost from litter. Soil organic matter also formed at the end of decomposition, when both non-structural and structural compounds were lost at similar rates. We conclude that two pathways yield soil organic matter efficiently. A dissolved organic matter–microbial path occurs early in decomposition when litter loses mostly non-structural compounds, which are incorporated into microbial biomass at high rates, resulting in efficient soil organic matter formation. An equally efficient physical-transfer path occurs when litter fragments move into soil.
Keywords: Biogeochemistry; Environmental chemistry; Stable isotope analysis

Functional differences between dominant grasses drive divergent responses to large herbivore loss in mesic savanna grasslands of North America and South Africa - Forrestel, E.J.; M.J. Donoghue; M.D. Smith (Journal of Ecology, 2015)
Grazing and fire are disturbances integral to the evolution and maintenance of savanna grasslands. Humans are altering or completely eliminating these disturbance regimes at a global scale, with important consequences for savanna ecosystem structure and function. It is unknown whether the alteration of these disturbance regimes will have similar effects on grass communities of savanna grasslands in different geographic regions that vary in their biogeographic and evolutionary histories, as well as in the diversity of extant grazers. Here, we examined the effects of large herbivore loss on different aspects of grass community structure – taxonomic, phylogenetic and functional – across a range of fire frequencies in C4-dominated mesic savanna grassland sites of North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). The goal of the study was to determine whether the loss of large herbivores exerted a consistent effect on the grass communities of two physiognomically similar grasslands with different biogeographic and grazing histories. The removal of large herbivores resulted in divergent responses in the grass communities at Konza and Kruger that was consistent across fire treatments. At Konza, there was a rapid and significant response to grazing exclusion while the response was muted and transient at Kruger. Functional syndromes associated with grazing resistance were generally conserved across sites, and it was the functional strategies of the dominant species at each site that drove the divergent responses. Further, our study supports the hypothesis that grazing and aridity may be selective forces that act in parallel as those species that were grazing resistant also occupied drier niches. Synthesis. Our study demonstrates that savanna grassland communities with different biogeographic and grazing histories respond differently to the removal of large herbivores and that climate, fire and grazing are interactive forces in maintaining savanna grassland diversity and function. We show that the functional attributes of the dominant grasses, which are in part driven by the biogeographic and grazing history experienced, are the most relevant in predicting the response of savanna ecosystems to the loss of large herbivores.
Keywords: phylogeny

Functional trait expression of grassland species shift with short- and long-term nutrient additions - Kimberly J. La Pierre; M.D. Smith (Plant Ecology, 2015)
Humans are altering nutrient availability worldwide, likely affecting plant trait expression, with consequences for community composition and ecosystem function. Here, we examined the responses of plant species dominant under ambient nutrient conditions (baseline species) versus those that become dominant under increased nutrient conditions (enriched species) in a tallgrass prairie ecosystem. The expression of 8 functional traits was quantified for 3 baseline and 3 enriched species within one short-term and one long-term nutrient addition experiment. We found that enriched species occupied a trait space characterized by traits that generally correspond with faster growth rates than baseline species. Additionally, the enriched species shifted in their trait expression relative to the control more than the baseline species with nutrient additions, particularly within the long-term experiment. The trait space shifts of individual species with nutrient additions scaled up to affect community aggregate trait values within both experiments. However, traits that responded to nutrient additions at the community level were not strong predictors of aboveground net primary productivity (ANPP) within the short-term experiment. In contrast, in the long-term experiment, one response trait (community aggregate height) strongly correlated with variation in ANPP with nutrient additions. The link between plant functional traits and community and ecosystem responses to chronic nutrient additions shown here will provide important insight into key mechanisms driving grassland responses to global change.
Keywords: Baseline species; Effect trait; Enriched species; Nutrient addition; Response trait; tallgrass prairie

Fundamental spatial and temporal disconnections in the hydrology of an intermittent prairie headwater network - Costigan, K.H.; Daniels, M.D.; W. K. Dodds (Journal of Hydrology, 2015)
We characterize the hydrology of intermittent prairie headwater streams of the Konza Prairie Biological Station (Konza) located in northeastern Kansas, USA. Flow records from four gaging stations were used to quantify flow intermittence and mean and peak annual discharges. Gage sites used in this analysis are classified as harshly intermittent with all sites having over 90 days of zero-flow annually. The largest basin had the fewest zero-flow days and the shortest durations of zero-flow while the smallest basin had the most zero-flow days and the highest frequency zero-flow durations. There were strong correlations between total annual precipitation and the total number of zero-flow days and the number of zero-flow periods. Correlations were less strong between the Palmer Drought Severity Index (PDSI) and the number of zero-flow days and between PDSI and the number of zero-flow periods. Basin-averaged total annual precipitation poorly predicted mean annual and peak annual discharges. Double mass plots of streamflow to precipitation and streamflow in the headwaters to the receiving stream demonstrate many instances of flow desynchronization. Results of this study suggest that local watershed-scale processes, such as groundwater storage in limestone and alluvial strata, dynamic infiltration flow paths, and soil moisture conditions, produce a threshold-driven hydrologic response, decoupling the headwater hydrologic regimes from sub-annual weather patterns.
Keywords: Flood; Great Plains; Intermittent; prairie; Temporary stream

Global environmental change and the nature of aboveground net primary productivity responses: insights from long-term experiments - M.D. Smith; Kimberly J. La Pierre; Scott. L. Collins; Alan K. Knapp; Gross, K.L.; Barrett, J.E.; Frey, S.D.; Gough, L.; Miller, R.J.; Morris, J.T.; Rustad, L.E.; Yarie, J. (Oecologia, 2015)
Many global change drivers chronically alter resource availability in terrestrial ecosystems. Such resource alterations are known to affect aboveground net primary production (ANPP) in the short term; however, it is unknown if patterns of response change through time. We examined the magnitude, direction, and pattern of ANPP responses to a wide range of global change drivers by compiling 73 datasets from long-term (>5 years) experiments that varied by ecosystem type, length of manipulation, and the type of manipulation. Chronic resource alterations resulted in a significant change in ANPP irrespective of ecosystem type, the length of the experiment, and the resource manipulated. However, the pattern of ecosystem response over time varied with ecosystem type and manipulation length. Continuous directional responses were the most common pattern observed in herbaceous-dominated ecosystems. Continuous directional responses also were frequently observed in longer-term experiments (>11 years) and were, in some cases, accompanied by large shifts in community composition. In contrast, stepped responses were common in forests and other ecosystems (salt marshes and dry valleys) and with nutrient manipulations. Our results suggest that the response of ANPP to chronic resource manipulations can be quite variable; however, responses persist once they occur, as few transient responses were observed. Shifts in plant community composition over time could be important determinants of patterns of terrestrial ecosystem sensitivity, but comparative, long-term studies are required to understand how and why ecosystems differ in their sensitivity to chronic resource alterations.
Keywords: Aboveground productivity; Hierarchical response framework (HRF); Long-Term Ecological Research (LTER) Network; Nutrient addition; Precipitation manipulation

Grassland productivity limited by multiple nutrients - Fay, P.A.; Prober, S.M.; Harpole, W.S.; Knops, J.M.H.; J.D. Bakker; E.T. Borer; Lind, E.M.; MacDougall, A.S.; Seabloom, E.W.; Wragg, P.D.; P. Adler; D.M. Blumenthal; et al. (Nature Plants, 2015)
Terrestrial ecosystem productivity is widely accepted to be nutrient limited1. Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)2,3, the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized4,​5,​6,​7,​8. However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μ co-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment.

Influence of drought on growing season carbon and water cycling with changing land cover - Logan, K.E.; N. Brunsell (Agricultural and Forest Meteorology, 2015)
Grasslands around the world are experiencing increased woody encroachment while drought frequency and severity is expected to increase with climate change. These processes will result in changes in the local carbon, water, and energy balances. Two closely located eddy covariance towers on native prairie sites in Kansas with differing burn regimes provided a unique opportunity to investigate those changes with minimal confounding climate factors. Daytime turbulent fluxes were analyzed throughout the growing season during two wet years (2008, 2009) and one drought year (2011). The site experiencing more woody encroachment (K4B) was a greater carbon sink every year, especially in 2011, when the annually burned site (KON) became a negligible sink and potential source of carbon. K4B also had greater seasonal water use efficiency (WUE) at all times except during drought and when burned. Evidence of water loss from deeper, stored sources was shown at K4B through cumulative evaporative loss that exceeded precipitation during drought conditions. Changes in the nature of the turbulent fluxes were also investigated through deviations from similarity theory, quadrant analysis, and wavelet decomposition. Wavelet analysis determined the size of eddies primarily involved in net exchange, showing differences between sites across small to medium scales (average diameter of 4.0–108 m). Increased surface heterogeneity and roughness with woody encroachment was seen through smaller eddy size of maximum transport and slightly weakened applicability of similarity theory at K4B. Eddy size decreased over the course of the growing season, in a strikingly inverse relation to grass leaf area index, likely corresponding to greater canopy height and roughness. Variance of the correlation between carbon and water, indicative of more variable plant productivity, is much greater across all scales in 2011 at KON only. Overall, results indicate woody encroachment increases resilience to drought. Though carbon sequestration remains stronger at the woody encroachment site, it comes at the cost of far increased water loss, including from deeper groundwater resources, which could prove detrimental in combination with predicted climate change.
Keywords: Drought; Eddy covariance; Turbulence; Water use efficiency

Invasibility of a mesic grassland depends on the time-scale of fluctuating resources - Koerner, S.E.; M.L. Avolio; Chang, C.C.; Grey, J.; D.L. Hoover; M.D. Smith (Journal of Ecology, 2015)
1. Global change is increasing the frequency and magnitude of resource fluctuations (pulses) at multiple time-scales. According to the fluctuating resource availability hypothesis (FRAH), susceptibility of an ecosystem to invasion (i.e. invasibility) is expected to increase whenever resource supply exceeds that which is utilized by native communities. Thus, global change has the potential to increase invasibility around the world. 2. Here, we test the FRAH by adding seeds of a target invader grass species to a long-term climate change experiment manipulating precipitation pulse size in tallgrass prairie in Kansas, USA. 3. Our experimental work yielded three important findings. First, contrary to predictions of the FRAH, invasibility was reduced with short time-scale resource pulses (intra-annual time-scale). Secondly, we found evidence to suggest that at inter-annual time-scales, the FRAH is supported. Wet years resulted in an increase in the number of established seedlings as well as the number of seedlings that persisted to the end of the season. Finally, we found that invasibility was positively related to native community richness and the density of individuals in the community suggesting that native communities facilitate establishment of invader species. Perhaps more importantly, results from this 10-year invasion study also show that resource availability drives invasion and that the biotic filters of plant community structure and diversity are secondary. 4. Synthesis. Our findings suggest that intensification of precipitation regimes may enhance resistance to invasion at intra-annual time-scales, but will have opposing effects if precipitation regimes include more wet years.

Invertebrate, not small vertebrate, herbivory interacts with nutrient availability to impact tallgrass prairie community composition and forb biomass - Kimberly J. La Pierre; Anthony Joern; M.D. Smith (Oikos, 2015)
The effects of herbivores and their interactions with nutrient availability on primary production and plant community composition in grassland systems is expected to vary with herbivore type. We examined the effects of invertebrate and small vertebrate herbivores and their interactions with nutrient availability on grassland plant community composition and aboveground biomass in a tallgrass prairie ecosystem. The abundance of forbs relative to grasses increased with invertebrate herbivore removals. This increase in forb abundance led to a shift in community composition, where invertebrate removals resulted in greater plant species evenness as well as a divergence in composition among plots. In contrast, vertebrate herbivore removals did not affect plant community composition or aboveground biomass. Nutrient additions alone resulted in a decrease in plant species richness and an increase in the abundance of the dominant grass, but the dominant grass species did not greatly increase in abundance when nutrient additions were combined with invertebrate removals. Rather, several subdominant forbs came to dominate the plant community. Additionally, the combined nutrient addition and invertebrate herbivore removal treatment increased forb biomass, suggesting that invertebrate herbivores suppress the responses of forb species to chronic nutrient additions. Overall, the release of forbs from invertebrate herbivore pressure may result in large shifts in species composition, with consequences for aboveground biomass and forage quality due to altered grass:forb ratios in grassland systems.

Long-term changes in structure and function of a tropical headwater stream following a disease-driven amphibian decline - Rantala, H.M.; Nelson, A.M.; Fulgoni, J.N.; M.R. Whiles; Hall, R.O.; W. K. Dodds; Verburg, P.; Huryn, A.; Pringle, C..; Kilham, S.S.; Lips, K.R.; Colon-Gaud, C.; et al. (Freshwater Biology, 2015)
1. Taxonomic and functional diversity in freshwater habitats is rapidly declining, but we know little about how such declines will ultimately affect ecosystems. Neotropical streams are currently experiencing massive losses of amphibians, with many losses linked to the chytrid fungus, Batrachochytrium dendrobatidis (Bd). 2. We examined the ecological consequences of the disease-driven loss of amphibians from a Panamanian stream. We quantified basal resources, macroinvertebrates, N uptake and fluxes through food-web components and ecosystem metabolism in 2012 and 2014 and compared them to pre-decline (2006) and 2 year post-decline (2008) values from a prior study. 3. Epilithon biomass accrued after the decline, more than doubling between 2006 and 2012, but then decreased fivefold from 2012 to 2014. In contrast, suspended particulate organic matter (SPOM) concentrations declined continuously after the amphibian decline through 2014. 4. Biomass of filter-feeding, grazing and shredding macroinvertebrates decreased from 2006 to 2014, while collector–gatherers increased during the same time period. Macroinvertebrate taxa richness decreased from 2006 (52 taxa) to 2012 (30 taxa), with a subsequent increase to 51 taxa in 2014. 5. Community respiration, which initially decreased after the amphibian decline, remained lower than pre-decline in 2012 but was greater than pre-decline values in 2014. Gross primary production remained low and similar among years, while inline image uptake length in both 2012 and 2014 was longer than pre-decline. Nitrogen flux to epilithon increased after the decline and continued to do so through 2014, but N fluxes to fine particulate organic matter and SPOM decreased and remained low. 6. Our findings underscore the importance of studying the ecological consequences of declining biodiversity in natural systems over relatively long time periods. There was no evidence of functional redundancy or compensation by other taxa after the loss of amphibians, even after 8 years.

Mutualism-parasitism paradigm synthesized from results of root-endophyte models - Mandyam, K.G.; A. Jumpponen (Frontiers in Microbiology, 2015)
Plant tissues host a variety of fungi. One important group is the dark septate endophytes (DSEs) that colonize plant roots and form characteristic intracellular structures – melanized hyphae and microsclerotia. The DSE associations are common and frequently observed in various biomes and plant taxa. Reviews suggest that the proportion of plant species colonized by DSE equal that colonized by AM and microscopic studies show that the proportion of the root system colonized by fungi DSE can equal, or even exceed, the colonization by AM fungi. Despite the high frequency and suspected ecological importance, the effects of DSE colonization on plant growth and performance have remained unclear. Here, we draw from over a decade of experimentation with the obscure DSE symbiosis and synthesize across large bodies of published and unpublished data from Arabidopsis thaliana and Allium porrum model systems as well as from experiments that use native plants to better resolve the host responses to DSE colonization. The data indicate similar distribution of host responses in model and native plant studies, validating the use of model plants for tractable dissection of DSE symbioses. The available data also permit empirical testing of the environmental modulation of host responses to DSE colonization and refining the “mutualism-parasitism-continuum” paradigm for DSE symbioses. These data highlight the context dependency of the DSE symbioses: not only plant species but also ecotypes vary in their responses to populations of conspecific DSE fungi – environmental conditions further shift the host responses similar to those predicted based on the mutualism-parasitism-continuum paradigm. The model systems provide several established avenues of inquiry that permit more detailed molecular and functional dissection of fungal endophyte symbioses, identifying thus likely mechanisms that may underlie the observed host responses to endophyte colonization.

Mycorrhizal phenotypes and the law of the minimum - Johnson, N.C.; G.T. Wilson; Wilson, J.A.; Miller, R.M.; M. Bowker (New Phytologist, 2015)
Mycorrhizal phenotypes arise from interactions among plant and fungal genotypes and the environment. Differences in the stoichiometry and uptake capacity of fungi and plants make arbuscular mycorrhizal (AM) fungi inherently more nitrogen (N) limited and less phosphorus (P) limited than their host plants. Mutualistic phenotypes are most likely in P-limited systems and commensal or parasitic phenotypes in N-limited systems. Carbon (C) limitation is expected to cause phenotypes to shift from mutualism to commensalism and even parasitism. Two experiments compared the influence of fertilizer and shade on mycorrhizas in Andropogon gerardii across three naturally N-limited or P-limited grasslands. A third experiment examined the interactive effects of N and P enrichment and shade on A. gerardii mycorrhizas. Our experiments generated the full spectrum of mycorrhizal phenotypes. These findings support the hypothesis that mutualism is likely in P-limited systems and commensalism or parasitism is likely in N-limited systems. Furthermore, shade decreased C-assimilation and generated less mutualistic mycorrhizal phenotypes with reduced plant and fungal biomass. Soil fertility is a key controller of mycorrhizal costs and benefits and the Law of the Minimum is a useful predictor of mycorrhizal phenotype. In our experimental grasslands arbuscular mycorrhizas can ameliorate P-limitation but not N-limitation.
Keywords: stoichiometry

Patch-burn grazing effects on the ecological integrity of tallgrass prairie streams - Jackson, K.E.; M.R. Whiles; W. K. Dodds; Reeve, J.D.; Vandermyde, J.M.; Rantala, H.M. (Journal of Environment Quality, 2015)
Conversion to agriculture, habitat fragmentation, and the loss of native grazers have made tallgrass prairie one of the most endangered ecosystems. One management option for the remaining prairie parcels, patch-burn grazing (PBG), applies a controlled burn to a portion of the prairie to attract cattle, creating a mosaic of more- and less-grazed patches. Although beneficial to cattle and grassland birds, the potential impacts of PBG on streams have not been studied, and a holistic approach is needed to ensure against adverse effects. We used a Before-After-Control-Impact design to assess potential impacts of PBG with and without riparian protection on tallgrass prairie headwater streams. We sampled stream macroinvertebrates and benthic organic matter 2 yr before and 2 yr during PBG treatments on two grazed watersheds with riparian fencing (fenced), two unfenced grazed watersheds (unfenced), and two ungrazed (control) watersheds. Very fine benthic organic matter increased significantly (51%) in unfenced streams compared with controls ( < 0.007), and fine particulate organic matter (<1 mm and >250 µm) increased 3-fold in the unfenced streams compared with controls ( = 0.008). The contribution of fine inorganic sediments to total substrata increased 28% in unfenced streams during PBG, which was significantly different from controls ( = 0.03). Additionally, the abundance of Ephemeroptera, Plecoptera, and Trichoptera taxa decreased from 7635 to 687 individuals m in unfenced streams, which was significantly lower than in control streams ( = 0.008). Our results indicate that PBG adversely influences prairie streams through sediment inputs and reductions in sensitive invertebrate taxa, but riparian fencing can alleviate these impacts.

Plant diversity predicts beta but not alpha diversity of soil microbes across grasslands worldwide - Prober, S.M.; Leff, J.W.; Bates, S.T.; E.T. Borer; Firn, J.; Harpole, W.S.; Lind, E.M.; Seabloom, E.W.; P. Adler; J.D. Bakker; E.E Cleland; DeCrappeo, N.M.; et al. (Ecology Letters, 2015)
Aboveground–belowground interactions exert critical controls on the composition and function of terrestrial ecosystems, yet the fundamental relationships between plant diversity and soil microbial diversity remain elusive. Theory predicts predominantly positive associations but tests within single sites have shown variable relationships, and associations between plant and microbial diversity across broad spatial scales remain largely unexplored. We compared the diversity of plant, bacterial, archaeal and fungal communities in one hundred and forty-five 1 m2 plots across 25 temperate grassland sites from four continents. Across sites, the plant alpha diversity patterns were poorly related to those observed for any soil microbial group. However, plant beta diversity (compositional dissimilarity between sites) was significantly correlated with the beta diversity of bacterial and fungal communities, even after controlling for environmental factors. Thus, across a global range of temperate grasslands, plant diversity can predict patterns in the composition of soil microbial communities, but not patterns in alpha diversity.

Plant responses to grazer-mediated habitat alterations in tallgrass prairie - Zahner, A. (Kansas State University, 2015)
The effects of bison activities on forb diversity and cover have been well-established, but less is known about how forb life history is altered by bison-mediated habitat changes. This study had three main objectives: 1) to evaluate the hypothesis that release from aboveground competition with grasses may contribute to the increased cover and diversity of forbs in prairie grazed by bison relative to ungrazed prairie, 2) to determine whether differences in forb reproductive effort between grazed and ungrazed habitats were size-dependent, and 3) to look for evidence of a trade-off between allocation to vegetative and sexual reproduction. The growth, biomass allocation, and sexual reproduction of six common unpalatable perennial species were measured and compared between bison-grazed and ungrazed tallgrass prairie burned at 2-year intervals: Ambrosia psilostachya, Artemisia ludoviciana, Baptisia australis, Psoralidium tenuiflorum, Solidago canadensis, and Vernonia baldwinii. Vegetative reproduction was also measured for B. australis¸ S. canadensis, and V. baldwinii. Light availability, canopy density and height, and percent cover of neighboring plants were measured in each studied individual’s immediate neighborhood and compared between habitats to establish the possibility of differing aboveground competition. Aboveground competition may be lower in bison-grazed habitats, as evidenced by differences in habitat characteristics and plant performance found in this study. In bison-present habitats, sexual reproduction was elevated for all six species and average plant size was greater for all species except A. psilostachya. Vegetative reproduction was not clearly different between habitats for all three species examined. Sexual reproduction increased with size for all species, and the relationship differed significantly between habitats for all species except A. psilostachya. Allocation to vegetative reproduction was not generally related to aboveground biomass, nor was there a clear trade-off between allocation to vegetative and sexual reproduction. The results of this study provide evidence that release from aboveground competition with grasses promotes the growth and sexual reproduction of the studied species of forb, and that differences in sexual reproduction are not entirely size-dependent. Patterns in allocation to vegetative reproduction were less clear and were not clearly tied to sexual reproductive allocation.
Keywords: Competition; forb; Grazing; Life history; Resource allocation; tallgrass prairie

Plant species’ origin predicts dominance and response to nutrient enrichment and herbivores in global grasslands - Seabloom, E.W.; E.T. Borer; Buckley, Y.; Cleland, E.E.; Davies, K.F.; Firn, J.; Harpole, W.S.; Hautier, Y.; Lind, E.; MacDougall, A.S.; Orrock, J.L.; Prober, S.M.; et al. (Nature Communications, 2015)
Exotic species dominate many communities; however the functional significance of species’ biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands.
Keywords: Biological sciences; ecology; Plant sciences

Quantifying ambient nitrogen uptake and functional relationships of uptake versus concentration in streams: a comparison of stable isotope, pulse, and plateau approaches - Trentman, M.T.; W. K. Dodds; Fencl, J.S.; Gerber, K.; Guarneri, J.; Hitchman, S.M.; Peterson, Z.; Rüegg, J. (Biogeochemistry, 2015)
Nutrient releases and spiraling metrics are frequently used to quantify the downstream transport of nutrients and to better understand the effects of anthropogenic inputs to downstream waters. Ambient uptake rates in streams can be measured through stable isotope enrichments, while pulse and plateau additions can estimate such rates via extrapolation and modeling techniques, respectively. Data from these releases can be used to estimate ambient uptake rates from nutrient additions and possibly determine the functional relationships between nutrient concentrations and uptake rates. Here, we compared estimated ambient rates calculated from established pulse and plateau approaches, results obtained from new modeling approaches, and rates at ambient concentrations from stable isotope enrichments. Comparative releases of NH4Cl and 15NH4Cl were conducted in four experimental reaches across the grassland Kings Creek and urban Campus Creek, KS. Nutrient uptake was predominantly linear with increasing ammonium. Estimated ambient uptake rates varied among sites, release methods, and data analysis approaches. However, plateau ambient rates from new modeling approaches matched closely with measured ambient rates from isotope enrichments at three sites, suggesting that modeled plateau data may be best for a first look at determining nutrient uptake rates at an individual site. Limitations and benefits of each approach vary; however, baseflow discharge may be a key driver when choosing a method. If possible, multiple methods should be attempted at each location and under each novel set of conditions to determine the best approach prior to designing and implementing a more extensive series of measurements.
Keywords: Ammonium uptake; nutrient spiraling; TASCC; uptake length

Recovery of whole soil conditions through restoration from agriculture and its role in mediating plant-plant competition - Scott, D.A. (Southern Illinois University Carbondale, 2015)

Scraping the bottom of the barrel: are rare high throughput sequences artifacts? - Brown, S.P.; Veach, A.M.; Rigdon-Huss, A.R.; Grond, K.; Lickteig, S.K.; Lothamer, K.; Oliver, A.K.; A. Jumpponen (Fungal Ecology, 2015)
Metabarcoding data generated using next-generation sequencing (NGS) technologies are overwhelmed with rare taxa and skewed in Operational Taxonomic Unit (OTU) frequencies comprised of few dominant taxa. Low frequency OTUs comprise a rare biosphere of singleton and doubleton OTUs, which may include many artifacts. We present an in-depth analysis of global singletons across sixteen NGS libraries representing different ribosomal RNA gene regions, NGS technologies and chemistries. Our data indicate that many singletons (average of 38 % across gene regions) are likely artifacts or potential artifacts, but a large fraction can be assigned to lower taxonomic levels with very high bootstrap support (∼32 % of sequences to genus with ≥90 % bootstrap cutoff). Further, many singletons clustered into rare OTUs from other datasets highlighting their overlap across datasets or the poor performance of clustering algorithms. These data emphasize a need for caution when discarding rare sequence data en masse: such practices may result in throwing the baby out with the bathwater, and underestimating the biodiversity. Yet, the rare sequences are unlikely to greatly affect ecological metrics. As a result, it may be prudent to err on the side of caution and omit rare OTUs prior to downstream analyses.
Keywords: fungi; High-throughput sequencing; Rare biosphere; Singleton

Soil Degradation: Will Humankind Ever Learn? - Karlen, Douglas; C. W. Rice (Sustainability, 2015)

A statistical approach for predicting grassland degradation in disturbance-driven landscapes - Jacquin, Anne; Goulard, Michel; Hutchinson, J.M.S.; Hutchinson, S.L. (2015 8th International Workshop on the Analysis of Multitemporal Remote Sensing Images (Multi-Temp), 2015)
The relationship between fire and long-term trends in tallgrass prairie vegetation was assessed at Fort Riley and Konza Prairie Biological Station (KPBS) in Kansas. Linear trends of surface greenness were previously estimated using BFAST and MODIS MOD13Q1 NDVI composite images from 2001 to 2010. To explain trends, fire frequency and seasonality (fire regime) was determined and each site was divided into spatial strata using administrative or management units. Generalized linear models (GLM) were used to explain trends by fire regime and/or stratification. Spatialized versions of GLMs were also computed address unexplained spatial components. Non-spatial models for FRK showed fire regime explained only 4% of trends compared to strata (7-26%). At KPBS, fire regime and spatial stratification explained 14% and 39%, respectively. At both sites, improvements in performance were minimal using both fire and strata as explanatory variables. Model spatialization resulted in a 5% improvement at FRK, but with weak spatial structure in the residuals, and was not necessary at KPBS as the existing stratification most of the spatial structure in model residuals. All models at KPBS performed better for each explanatory variable and combination tested. Fire has only a marginal effect on vegetation trends at FRK despite its widespread use as a grassland management tool to improve vegetation health, and explains much more of the trends at KPBS. Analysis of predictors from spatial models with existing stratification yielded an approach with fewer strata but similar performance and may provide insight about additional explanatory variables omitted from this analysis.

Stoichiometric homeostasis predicts plant species dominance, temporal stability and responses to global change - Yu, Q.; K.R. Wilcox; Kimberly J. La Pierre; Alan K. Knapp; Han, X.; M.D. Smith (Ecology, 2015)
Why some species are consistently more abundant than others, and predicting how species will respond to global change, are fundamental questions in ecology. Long-term observations indicate that plant species with high stoichiometric homeostasis for nitrogen (HN), i.e., the ability to decouple foliar N levels from variation in soil N availability, were more common and stable through time than low HN species in a central US grassland. However, with 9-yrs of nitrogen addition, species with high HN decreased in abundance, while those with low HN increased in abundance. In contrast, in climate change experiments simulating a range of forecast hydrologic changes - extreme drought (2-yrs), increased rainfall variability (14-yrs), and chronic increases in rainfall (21-yrs) - plant species with the highest HN were least responsive to changes in soil water availability. These results suggest that HN may be predictive of plant species success and stability, and how plant species and ecosystems will respond to global-change driven alterations in resource availability.

The Stream Biome Gradient Concept: factors controlling lotic systems across broad biogeographic scales - W. K. Dodds; K. B. Gido; M.R. Whiles; Daniels, M.D.; Grudzinski, B.P. (Freshwater Science., 2015)
We propose the Stream Biome Gradient Concept as a way to predict macroscale biological patterns in streams. This concept is based on the hypothesis that many abiotic and biotic features of streams change predictably along climate (temperature and precipitation) gradients because of direct influences of climate on hydrology, geomorphology, and interactions mediated by terrestrial vegetation. The Stream Biome Gradient Concept generates testable hypotheses related to continental variation among streams worldwide and allows aquatic scientists to understand how results from one biome might apply to a less-studied biome. Some predicted factors change monotonically across the biome/climate gradients, whereas others have maxima or minima in the central portion of the gradient. For example, predictions across the gradient from drier deserts through grasslands to wetter forests include more permanent flow, less bare ground, lower erosion and sediment transport rates, decreased importance of autochthonous C inputs to food webs, and greater stream animal species richness. In contrast, effects of large ungulate grazers on streams are expected to be greater in grasslands than in forests or deserts, and fire is expected to have weaker effects in grassland streams than in desert and forest streams along biome gradients with changing precipitation and constant latitude or elevation. Understanding historic patterns among biomes can help describe the evolutionary template at relevant biogeographic scales, can be used to broaden other conceptual models of stream ecology, and could lead to better management and conservation across the broadest scales.
Keywords: biogeography; biome; lotic; macro-scale; macrosystems; stream

Stream microbial diversity in response to environmental changes: review and synthesis of existing research - Lydia H. Zeglin (Frontiers in Microbiology, 2015)
The importance of microbial activity to ecosystem function in aquatic ecosystems is well established, but microbial diversity has been less frequently addressed. This review and synthesis of 100s of published studies on stream microbial diversity shows that factors known to drive ecosystem processes, such as nutrient availability, hydrology, metal contamination, contrasting land-use and temperature, also cause heterogeneity in bacterial diversity. Temporal heterogeneity in stream bacterial diversity was frequently observed, reflecting the dynamic nature of both stream ecosystems and microbial community composition. However, within-stream spatial differences in stream bacterial diversity were more commonly observed, driven specifically by different organic matter (OM) compartments. Bacterial phyla showed similar patterns in relative abundance with regard to compartment type across different streams. For example, surface water contained the highest relative abundance of Actinobacteria, while epilithon contained the highest relative abundance of Cyanobacteria and Bacteroidetes. This suggests that contrasting physical and/or nutritional habitats characterized by different stream OM compartment types may select for certain bacterial lineages. When comparing the prevalence of physicochemical effects on stream bacterial diversity, effects of changing metal concentrations were most, while effects of differences in nutrient concentrations were least frequently observed. This may indicate that although changing nutrient concentrations do tend to affect microbial diversity, other environmental factors are more likely to alter stream microbial diversity and function. The common observation of connections between ecosystem process drivers and microbial diversity suggests that microbial taxonomic turnover could mediate ecosystem-scale responses to changing environmental conditions, including both microbial habitat distribution and physicochemical factors.
Keywords: ecosystem structure and function; lotic ecosystems; microbial diversity; rivers; streams

Structure of trophic and mutualistic networks across broad environmental gradients - Welti, E.L.; Anthony Joern (Ecology and Evolution, 2015)
This study aims to understand how inherent ecological network structures of nestedness and modularity vary over large geographic scales with implications for community stability. Bipartite networks from previous research from 68 locations globally were analyzed. Using a meta-analysis approach, we examine relationships between the structure of 22 trophic and 46 mutualistic bipartite networks in response to extensive gradients of temperature and precipitation. Network structures varied significantly across temperature gradients. Trophic networks showed decreasing modularity with increasing variation in temperature within years. Nestedness of mutualistic networks decreased with increasing temperature variability between years. Mean annual precipitation and variability of precipitation were not found to have significant influence on the structure of either trophic or mutualistic networks. By examining changes in ecological networks across large-scale abiotic gradients, this study identifies temperature variability as a potential environmental mediator of community stability. Understanding these relationships contributes to our ability to predict responses of biodiversity to climate change at the community level.
Keywords: trophic interactions

Thermal performance of larval longfin dace (Agosia chrysogaster), with implications for climate change - Troia, M.J.; Whitney, J.E.; K. B. Gido (Environmental Biology of Fishes, 2015)
Temperature is an important factor affecting the distribution of freshwater fishes. The longfin dace (Agosia chrysogaster) is endemic to the Gila River basin of the southwestern USA and northern Mexico and occupies a range of thermal environments from cool mountain tributaries to warm desert rivers but information about its thermal biology is limited, particularly for larvae. We quantified the effect of rearing temperature on survival, growth capacity, and critical thermal maximum (CTM) of larval longfin dace. Broodstocks of longfin dace were collected from two sites in the upper Gila River in New Mexico from which larvae were hatched and reared for 22 days in indoor aquaria at constant temperatures ranging from 18.0 to 31.0 °C. Growth capacity peaked at 27.0 °C and was 21 % greater for larvae hatched from the upstream compared to the downstream broodstock, indicating intraspecific variability in growth capacity. CTM increased with rearing temperature and ranged from 33.9 to 39.9 °C, indicating that thermal acclimation influences maximum thermal tolerance. CTM and acclimation response ratio of larvae are lower than those of adult longfin dace measured in a previous study, suggesting that larvae are more sensitive and less responsive to thermal stress than adults. Water temperatures in 2012 from six sites in the upper Gila River basin did not exceed 27.0 °C and larval growth capacities in May of 2012 ranged from 5 to 28 % of the maximum growth capacity. We assert that rising temperatures may increase larval growth rates, although this will depend on resource limitation and shifts in community interactions.
Keywords: Critical thermal maximum; GilaRiver; Growth capacity; Larval fish; Thermal acclimation

Timing is everything: temporal variation in floral scent, and its connections to pollinator behavior and female reproductive success in Phlox divaricata - Majetic, C.J.; Wiggam, S.D.; Ferguson, C.J.; Raguso, R.A. (American Midland Naturalist, 2015)
The study of floral traits and pollination for the plant genus Phlox has historically been focused on either surveys of general pollinator affinities across the genus or detailed research on pollinator-mediated evolution of floral color in a single species (Phlox drummondii). The purpose of this study was to explore a different kind of trait – floral scent – in Phlox divaricata, a species noted for its strong scent. Specifically, we predicted the diel emission patterns of floral scent might covary with the daily abundance of diurnal moths, identified in a previous study as the most important pollinators in a Konza Prairie population of P. divaricata. Consistent with this prediction, we documented peaks in median floral scent emissions at 1000–1200 and 1930–2130, coinciding with peaks in moth visitation and resulting seed production. Two groups of scent compounds contributed to this pattern; linalool and its associated lilac aldehyde/alcohol compounds (especially lilac aldehyde B) contributed a greater proportion to scent at 1000–1200, while aromatic compounds (including benzaldehyde and benzyl acetate) contributed a greater proportion to scent at 1930–2130 and other afternoon time periods. These volatiles are known floral attractants for several lepidopteran pollinators, including noctuid moths. However, there is an additional peak in pollinator abundance (Hemaris diurnal hawkmoths) and seed set at a time when scent production is relatively low (1400–1600) suggesting additional factors mediate both pollinator behavior and floral volatile emissions. Future studies of P. divaricata should test for the presence of destructive floral enemies that might be attracted by floral volatiles during mid-afternoon periods, as well as the importance of visual floral traits (color, shape) in attracting diurnal moths, an important functional group of pollinators that has received minimal attention in North America.

Vegetative reproduction and bud Bank dynamics of the perennial grass andropogon gerardii in mixed-grass and tallgrass prairie - Ott, J.P.; D.C. Hartnett (American Midland Naturalist, 2015)
Plant species with wide distributions may differ in their population dynamics across their range, especially in contrasting habitats. Most tiller recruitment of perennial grasses occurs vegetatively from the belowground bud bank rather than from seed. Seed reproduction often occurs under a narrower range of environmental conditions than vegetative reproduction. As a result flowering and seedling recruitment patterns of a species often differ between contrasting habitats and across its range. How vegetative reproduction and bud bank dynamics of a species vary between contrasting habitats has not been well studied and could explain the differences in its persistence and productivity between habitats. Therefore, the vegetative reproduction and dynamics of Andropogon gerardii, a dominant C4 perennial grass of the Great Plains of North America, were compared between tallgrass and northern mixedgrass prairie habitats. Bud production and tiller recruitment in 10 populations were examined throughout an annual growing cycle in the northern mixedgrass prairie of South Dakota. Bud bank characteristics, and individual and population performance were compared with previous work conducted in Kansas tallgrass prairie. Stage-structured matrix models examined population growth rates. Andropogon gerardii tillers produced lower numbers of buds and had lower flowering rates in mixedgrass prairie populations. The annual phenology of bud and tiller development was also contracted to fit within the shorter growing season in northern mixedgrass prairie. However, bud longevity and bud bank age structure were similar between habitats, both having buds that lived for > 2 y and multi-aged bud banks. Similar population growth rates occurred in both habitats despite lower individual performance of both flowering and vegetative reproductive capacity (i.e., bud production) in mixedgrass prairie populations. Lower regional productivity of A. gerardii in northern mixedgrass prairie than in tallgrass prairie does not appear to be due to differences in bud and tiller population growth. Instead, sparse or patchy suitable habitat and/or reduction in tiller size may explain its reduced productivity. Lower population growth rates may be observed in other habitats or in years with harsher environmental conditions that further lower individual performance.

Weather affects grasshopper population dynamics in continental grassland over annual and decadal periods - Jonas, J.L.; Wolesensky, W.; Anthony Joern (Rangeland Ecology and Management, 2015)
Understanding the complex dynamics of insect herbivores requires consideration of both exogenous and endogenous factors at multiple temporal scales. This problem is difficult due to differences in population responses among closely related taxa. Increased understanding of dynamic relationships between exogenous and endogenous factors will facilitate forecasting and suggest nodes in the life cycle of economically important species susceptible to intervention by managers. This study uses an information-theoretic approach to examine the contributions of weather and density to model population densities and growth rates of nine common grasshopper species from continental U.S. grassland over 25 years. In general, grass-feeding species and total grass-feeders as a functional group were most closely associated with weather during the year before hatching. Increased variability in prior growing season precipitation was associated with increased densities of Mermiria bivittata, Opeia obscura, Phoetaliotes nebrascensis, and the grass-feeding guild. Melanoplus sanguinipes densities tended to be smaller following warm fall seasons, while Amphitoruns coloradus declined during the positive phase of the North Atlantic Oscillation or after warmer than average winters. Population growth rate dynamics of all grouped species combinations were best explained by models including variability in precipitation during the prior year growing season. Large-scale Pacific Decadal Oscillation (PDO) patterns were also associated with growth rate dynamics of the mixed-feeding species group. Density showed a negative relationship with population growth rates of five species. This study indicates the importance of parental and diapause environmental conditions and the utility of incorporating long-term, readily obtained decadal weather indices for forecasting grasshopper densities and identifying critical years with regard to grasshopper management—at least to the degree that the past will continue to predict the future as global climates change.
Keywords: acrididae; atmospheric oscillations (NAO PDO SOI); density dependence; exogenous and endogenous feedbacks; grasshopper control; insect herbivores; population growth rate (R)

Woody plant encroachment, and its removal, impact bacterial and fungal communities across stream and terrestrial habitats in a tallgrass prairie ecosystem - Veach, A.M.; W. K. Dodds; A. Jumpponen (FEMS Microbiology Ecology, 2015)
Woody plant encroachment has become a global threat to grasslands and has caused declines in aboveground richness and changes in ecosystem function; yet we have a limited understanding on the effects of these phenomena on belowground microbial communities. We completed riparian woody plant removals at Konza Prairie Biological Station, Kansas and collected soils spanning land–water interfaces in removal and woody vegetation impacted areas. We measured stream sediments and soils for edaphic variables (C and N pools, soil water content, pH) and bacterial (16S rRNA genes) and fungal (ITS2 rRNA gene repeat) communities using Illumina MiSeq metabarcoding. Bacterial richness and diversity decreased with distance from streams. Fungal richness decreased with distance from the stream in wooded areas, but was similar across landscape position while Planctomycetes and Basidiomycota relative abundance was lower in removal areas. Cyanobacteria, Ascomycota, Chytridiomycota and Glomeromycota relative abundance was greater in removal areas. Ordination analyses indicated that bacterial community composition shifted more across land–water interfaces than fungi yet both were marginally influenced by treatment. This study highlights the impacts of woody encroachment restoration on grassland bacterial and fungal communities which likely subsequently affects belowground processes and plant health in this ecosystem.
Keywords: bacterial communities; fungal communities; land–water interface; tallgrass prairie; woody encroachment

Abrupt transition of mesic grassland to shrubland: evidence for thresholds, alternative attractors, and regime shifts - Z. Ratajczak; Jesse B. Nippert; Ocheltree, T.W. (Ecology, 2014)
Ecosystems with alternative attractors are susceptible to abrupt regime shifts that are often difficult to predict and reverse. In this study, we quantify multiple system dynamics to determine whether the transition of mesic grassland to shrubland, a widespread phenomenon, represents a linear reversible process, a nonlinear but reversible threshold process, or a transition between alternative attractors that is nonlinear and prone to hysteresis. Using a 28-yr data set with annual resolution and extensive spatial replication, we found that shrub cover is correlated with distinct thresholds of fire and C4 grass cover, resulting in temporal bimodality of shrub cover and abrupt shifts of shrub cover despite gradual changes in grass cover. These abrupt increases in shrub cover are the most rapid ever reported in grasslands, and illustrate internal thresholds that separate grasslands and shrublands. Nonlinear transitions from low to high shrub cover were also closely associated with positive feedback mechanisms that alter fire and competition (r2 = 0.65), suggesting that grasslands and shrublands could show hysteresis, and by definition exist as alternative attractors. Thus, the response of this ecosystem to anthropogenic activity should tend to be rapid, nonlinear, and perhaps difficult to reverse. Regime shifts in this mesic grassland were predictable: we found that grassland and shrubland attractors were differentiated by critical thresholds of ∼50–70% grass cover, 5–10% shrub cover, and a fire return interval of ∼3 yr. These thresholds may provide adaptive potential for managing nonlinear behavior in socio-ecological systems in a changing environment.

Agriculture, Forestry and Other Land Use (AFOLU) - Smith, P.; Bustamante, M.; Ahammad, H.; Clark, H.; Dong, H.; Elsiddig, E. A.; Haberl, H.; Harper, R.; J. House; M. Jafari; O. Masera; C. Mbow; et al. (Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, 2014)

Alternative spawning strategy and temperature for larval emergence of longfin dace (Agosia chrysogaster) in stream mesocosms - Troia, M.J.; Whitney, J.E.; K. B. Gido (The Southwestern Naturalist, 2014)
To determine if the strategy of spawning in saucer-like depressions is obligate or facultative for longfin dace (Agosia chrysogaster), we collected adults from four sites in the upper Gila River (southwestern New Mexico), stocked them in separate outdoor stream-mesocosms lined with cobble substrate, and made daily observations for the presence of saucer-nests and hatched larvae. Larvae were observed from three of the four mesocosms and emerged at temperatures ranging from 19.2–24.0°C. The absence of saucer-nests in all mesocosms throughout the study indicates that longfin dace can spawn over cobble substrate and have larvae hatch successfully, suggesting that longfin dace can use an alternate spawning strategy when sand substrate is not available for construction of saucer-nests.

Anthropogenic-based regional-scale factors most consistently explain plot-level exotic diversity in grasslands - MacDougall, A.S.; Bennett, J.R.; Firn, J.; Seabloom, E.W.; E.T. Borer; Lind, E.M.; Orrock, J.L.; Harpole, W.S.; Hautier, Y.; P. Adler; Cleland, E.; Davies, K.; et al. (Global Ecology and Biogeography, 2014)
Aim Evidence linking the accumulation of exotic species to the suppression of native diversity is equivocal, often relying on data from studies that have used different methods. Plot-level studies often attribute inverse relationships between native and exotic diversity to competition, but regional abiotic filters, including anthropogenic influences, can produce similar patterns. We seek to test these alternatives using identical scale-dependent sampling protocols in multiple grasslands on two continents. Location Thirty-two grassland sites in North America and Australia. Methods We use multiscale observational data, collected identically in grain and extent at each site, to test the association of local and regional factors with the plot-level richness and abundance of native and exotic plants. Sites captured environmental and anthropogenic gradients including land-use intensity, human population density, light and soil resources, climate and elevation. Site selection occurred independently of exotic diversity, meaning that the numbers of exotic species varied randomly thereby reducing potential biases if only highly invaded sites were chosen. Results Regional factors associated directly or indirectly with human activity had the strongest associations with plot-level diversity. These regional drivers had divergent effects: urban-based economic activity was associated with high exotic : native diversity ratios; climate- and landscape-based indicators of lower human population density were associated with low exotic : native ratios. Negative correlations between plot-level native and exotic diversity, a potential signature of competitive interactions, were not prevalent; this result did not change along gradients of productivity or heterogeneity. Main conclusion We show that plot-level diversity of native and exotic plants are more consistently associated with regional-scale factors relating to urbanization and climate suitability than measures indicative of competition. These findings clarify the long-standing difficulty in resolving drivers of exotic diversity using single-factor mechanisms, suggesting that multiple interacting anthropogenic-based processes best explain the accumulation of exotic diversity in modern landscapes.

Belowground bud banks of tallgrass prairie are insensitive to multi-year, growing-season drought - VanderWeide, B.L.; D.C. Hartnett; Carter, D.L. (Ecosphere, 2014)
In tallgrass prairie plant communities, new shoots are recruited from belowground bud banks, often in response to disturbance. We explored the contribution of belowground bud banks to grassland stability when perturbed by severe drought. We sought to quantify changes in bud bank density and demography, assess the contribution of the bud bank to aboveground net primary productivity, and compare shifts in above- and belowground plant community structure in response to drought. We experimentally reduced precipitation 76% from ambient levels for two years, and compared responses of drought plots to ambient and irrigated controls during the two years of drought and two years of recovery. We measured belowground bud bank density and aboveground shoot density, canopy cover, and aboveground net primary productivity. While aboveground net primary productivity and C4 grass flowering shoot density declined during drought, bud bank density was insensitive to drought. Rapid resilience of the aboveground plant community following cessation of drought appears to be mediated by the resistance of bud banks to drought. Shoot density, but not bud bank density, was positively correlated with total aboveground net primary productivity. Furthermore, proportional reductions in aboveground net primary productivity increased as shoot density increased. Plant community structure shifted both above- and belowground in response to precipitation treatments. Our results suggest that the response of perennial grasslands to drought may be mediated by the stable belowground bud bank, with shifts in abundance of individual species maintaining overall bud bank density and ecosystem function.

Biotic mechanisms of community stability shift along a precipitation gradient - Hallett, L.M.; Hsu, J.S.; Cleland, E.E.; Scott. L. Collins; Dickson, T.L.; Farrer, E.C.; Gherardi, L.A.; Gross, K.L.; Hobbs, R.J.; Turnbull, L.; K.N. Suding (Ecology, 2014)
Understanding how biotic mechanisms confer stability in variable environments is a fundamental quest in ecology, and one that is becoming increasingly urgent with global change. Several mechanisms, notably a portfolio effect associated with species richness, compensatory dynamics generated by negative species covariance and selection for stable dominant species populations can increase the stability of the overall community. While the importance of these mechanisms is debated, few studies have contrasted their importance in an environmental context. We analyzed nine long-term data sets of grassland species composition to investigate how two key environmental factors, precipitation amount and variability, may directly influence community stability and how they may indirectly influence stability via biotic mechanisms. We found that the importance of stability mechanisms varied along the environmental gradient: strong negative species covariance occurred in sites characterized by high precipitation variability, whereas portfolio effects increased in sites with high mean annual precipitation. Instead of questioning whether compensatory dynamics are important in nature, our findings suggest that debate should widen to include several stability mechanisms and how these mechanisms vary in importance across environmental gradients.

Cessation of burning dries soils long-term in a tallgrass prairie - Craine, J.M.; Jesse B. Nippert (Ecosystems, 2014)
Soil moisture is a critical variable in grassland function, yet how fire regimes influence ecohydrology is poorly understood. By altering productivity, species composition, and litter accumulation, fire can indirectly increase or decrease soil water depletion on a range of time scales and depths in the soil profile. To better understand how fire influences soil moisture in grasslands, we analyzed 28 years of soil moisture data from two watersheds in a central North American grassland which differ in their long-term fire frequency. Across 28 years, cessation of prescribed burning initially led to wetter soils, likely as litter accumulated and both transpiration and evaporation were suppressed. Long-term, cessation of burning led to soils drying more, especially at depths greater than 75 cm. The long-term drying of deep soils is consistent with the increase in woody species in the infrequently burned grassland as woody species likely have a greater reliance on soil water from deeper soil layers compared to co-occurring herbaceous species. Despite the ecohydrological changes associated with the cessation of prescribed burning, watersheds with different burn regimes responded similarly to short-term variation in climate variation. In both watersheds, low precipitation and high temperatures led to drier soils with greater responses in soil moisture to climate variation later in the season than earlier. There is no current evidence that the cessation of burning in this ecosystem will qualitatively alter how evapotranspiration responds to climate variation, but the use of deeper soil water by woody plants has the potential for greater transpiration during dry times. In all, modeling the depth-specific responses of soil moisture and associated ecosystem processes to changes in burn regimes will likely require including responses of plant community composition over short and long time scales.
Keywords: critical climate period; ecohydrology; Evapotranspiration; fire; Konza Prairie; soil moisture; woody species

Changes in plant community composition, not diversity, during a decade of nitrogen and phosphorus additions drive above-ground productivity in a tallgrass prairie - M.L. Avolio; Koerner, S.E.; Kimberly J. La Pierre; K.R. Wilcox; G.T. Wilson; M.D. Smith; Scott. L. Collins (Journal of Ecology, 2014)
Nutrient additions typically increase terrestrial ecosystem productivity, reduce plant diversity and alter plant community composition; however, the effects of P additions and interactions between N and P are understudied. We added both N (10 g m−2) and three levels of P (2.5, 5 and 10 g m−2) to a native, ungrazed tallgrass prairie burned biennially in northeastern Kansas, USA, to determine the independent and interactive effects of N and P on plant community composition and above-ground net primary productivity (ANPP). After a decade of nutrient additions, we found few effects of P alone on plant community composition, N alone had stronger effects, and N and P additions combined resulted in much larger effects than either alone. The changes in the plant community were driven by decreased abundance of C4 grasses, perhaps in response to altered interactions with mycorrhizal fungi, concurrent with increased abundance of non-N-fixing perennial and annual forbs. Surprisingly, this large shift in plant community composition had little effect on plant community richness, evenness and diversity. The shift in plant composition with N and P combined had large but variable effects on ANPP over time. Initially, N and N and P combined increased above-ground productivity of C4 grasses, but after 4 years, productivity returned to ambient levels as grasses declined in abundance and the community shifted to dominance by non-N-fixing and annual forbs. Once these forbs increased in abundance and became dominant, ANPP was more variable, with pulses in forb production only in years when the site was burned. Synthesis. We found that a decade of N and P additions interacted to drive changes in plant community composition, which had large effects on ecosystem productivity but minimal effects on plant community diversity. The large shift in species composition increased variability in ANPP over time as a consequence of the effects of burning. Thus, increased inputs of N and P to terrestrial ecosystems have the potential to alter stability of ecosystem function over time, particularly within the context of natural disturbance regimes.

Colonization and recovery of invertebrate ecosystem engineers during prairie restoration - Wodika, B.R.; S.G. Baer; Klopf, R.P. (Restoration Ecology, 2014)
Ants (Hymenoptera: Formicidae) and earthworms (Oligochaeta) are considered ecosystem engineers because they form biogenic structures in the soil that influence resource supply. The objectives of this study were to quantify recovery dynamics of these invertebrate groups across a chronosequence of restored prairies and elucidate whether changes in the abundance and biomass of ants and earthworms were related to key plant and ecosystem properties. We sampled ants and earthworms from cultivated fields, grasslands restored from 1 to 21 years, and native prairie. Ant abundance and biomass peaked between 5 and 8 years of restoration and abundance was 198 times greater than cultivated fields. Earthworm abundance increased linearly across the chronosequence and became representative of native prairie, but all earthworm populations were dominated by European species. Ant abundance and biomass were positively correlated with plant diversity and plant richness, whereas earthworm abundance biomass was only related to surface litter. These results demonstrate that earthworm abundance increases with time since cessation of cultivation and concomitant with prairie establishment, whereas the abundance and biomass of ants are more related to the structure of restored plant communities than time. The dominance of exotic earthworms in these restorations, coupled with their capacity to alter soil properties and processes may represent novel conditions for grassland development.
Keywords: ants; chronosequence; earthworms; Illinois; prairie; restoration; soil fauna

Comparing nondestructive and destructive methods of measuring leaf chlorophyll content: tracking changes in foliar chlorophyll of five Andropogon gerardii ecotypes (Poaceae) - Caudle, K.L.; Johnson, L.C.; S.G. Baer; Maricle, B.R. (Photosynthetica, 2014)

Contrasting sensitivities of two dominant C4 grasses to heat waves and drought - D.L. Hoover; M.D. Smith (Plant Ecology, 2014)
Heat waves and droughts are predicted to increase in frequency and intensity with climate change. However, we lack a mechanistic understanding of the independent and interactive effects of severe heat and water stress for most ecosystems. In a mesic tallgrass prairie ecosystem, we used a factorial experimental approach to assess ecophysiological and productivity responses of two dominant C4 grasses, Andropogon gerardii and Sorghastrum nutans, to a season-long drought and a mid-summer heat wave at four intensities. We hypothesized that drought would have greater impacts than heat waves, that combined effects would be greater than either factor alone, and that the dominant grasses would differ in their responses to heat and water heat stress. We detected significant reductions in photosynthesis, leaf water potential, and productivity with drought but few direct responses to the heat waves. Surprisingly, there was no additive effect of heat and water stress on any plant response. However, S. nutans was more sensitive than A. gerardii to drought. In this grassland, water stress will likely dominate photosynthetic and productivity responses caused by discrete drought and heat wave events, rather than direct or additive effects of heat stress, with differential sensitivity in these grasses altering future ecosystem structure and function.
Keywords: Climate change; Climate extremes; Mesic grassland; photosynthesis; productivity

Convergent and contingent community responses to grass source and dominance during prairie restoration across a longitudinal gradient - Klopf, R.P.; S.G. Baer; D.J. Gibson (Environmental Management, 2014)
Restoring prairie on formerly cultivated land begins by selecting propagule seed sources and the diversity of species to reintroduce. This study examined the effects of dominant grass propagule source (cultivar vs. non-cultivar) and sown propagule diversity (grass:forb sowing ratio) on plant community structure. Two field experiments were established in Kansas and Illinois consisting of identical split plot designs. Dominant grass source was assigned as the whole-plot factor, and sown dominance of grasses (five levels of seeded grass dominance) as the subplot factor. Species density, cover, and diversity were quantified for 5 years. The effect of dominant grass source on the cover of focal grasses, sown species, and volunteer species was contingent upon location, with variation between dominant grass sources observed exclusively in Kansas. Species density and diversity showed regionally convergent patterns in response to dominant grass source. Contrary to our hypotheses, total species density and diversity were not lower in the presence of grass cultivars, the grass source we had predicted would be more competitive. Sown grass dominance effects on the cover of the focal grass species were contingent upon location resulting from establishment corresponding better to the assigned treatments in Illinois. All other cover groups showed regionally convergent patterns, with lower cover of volunteers and higher cover of sown forbs, diversity, and species density in the lowest sown grass dominance treatment in both sites. Thus, decisions regarding the diversity of propagules to reintroduce had more consequence for plant community structure than cultivar or non-cultivar source of dominant grasses.
Keywords: Ecotype; grassland; restoration; Seed source

Convergent phylogenetic and functional responses to altered fire regimes in mesic savanna grasslands of North America and South Africa - Forrestel, E.J.; M.J. Donoghue; M.D. Smith (New Phytologist, 2014)
The importance of fire in the creation and maintenance of mesic grassland communities is well recognized. Improved understanding of how grasses – the dominant clade in these important ecosystems – will respond to alterations in fire regimes is needed in the face of anthropogenically driven climate and land-use change. Here, we examined how grass communities shift in response to experimentally manipulated fire regimes at multiple levels of community diversity – taxonomic, phylogenetic and functional – in C4-dominanted mesic savanna grassland sites with similar structure and physiognomy, yet disparate biogeographic histories. We found that the grass communities were similar in their phylogenetic response and aspects of their functional response to high fire frequency. Both sites exhibited phylogenetic clustering of highly abundant species in annually burned plots, driven by species of the Andropogoneae, and a narrow range of functional strategies associated with rapid post-fire regeneration in a high-light, nitrogen-limited environment. By examining multiple facets of diversity in a comparative context, we identified convergent phylogenetic and functional responses to altered fire regimes in two mesic savanna grasslands. Our results highlight the importance of a common filtering process associated with fire that is consistent across grasslands of disparate biogeographic histories and taxonomic representation.

Did selective breeding of a non-native grass promote invasiveness? - Grischkowsky, S.A. (Oklahoma State University, 2014)
Concerns with invasive species have included exotic forage grasses that have undergone extensive breeding through development programs for greater success of establishment. These grasses have been widely distributed for soil erosion control and livestock forage production throughout the United States and many of these species have become invasive in native habitats. To determine whether plant breeding procedures increased the invasiveness of these exotic grasses relative to their native counterparts, we assessed the competitiveness of an old world bluestem (Bothriochloa ischaemum ; OWB) a known invader of the Great Plains in the United States, relative to its "wildtype" from the Czech Republic, and two native tallgrass prairie grasses (big bluestem [Andropogon gerardii] and little bluestem [Schizachyrium scoparium]). To assess inter-and intraspecific competition a substitutive design greenhouse competition experiment was conducted in Stillwater, Oklahoma with partners from the Czech University of Life Sciences. Growth of the invasive B. ischaemum was enhanced when grown with the native S. scoparium. However, the Czech Republic wildtype did not exhibit increased production when grown in competition with natives compared to conspecifics, suggesting the extensive breeding of B. ischaemum may have enhanced its competitive abilities. To further assess plant-soil feedbacks we conducted a second greenhouse study which examined soil biotic communities using soil inoculums associated with either wildtype or invasive B. ischaemum cultivars. Growth and reproduction of native grass species, the wildtype, and invasive B. ischaemum were assessed 16 weeks following inoculation with soil microbial communities. Phospholipid and neutral lipid fatty acids were quantified at the end of the study to determine microbial biomass associated with each soil inoculum and species or cultivar combination. Total biomass production and abundance of AMF was enhanced when the wildtype was grown with inoculum associated with the invasive cultivar compared to wildtype inoculum, indicating the wildtype favors soil biotic communities associated with the invasive cultivar. When assessing responses of native grasses, A. gerardii illustrated greater production and abundance of AMF compared to S. scoparium suggesting seeding to A. gerardii may lead to greater success in grassland restorations following eradication of B. ischaemum, compared to restorations seeded to S. scoparium.
Keywords: ecology; natural resource management; range management

Differential effects of extreme drought on production and respiration: Synthesis and modeling analysis - Shi, Z.; Thomey, M.L.; Mowll, M.; Litvak, M.E.; N. Brunsell; Scott. L. Collins; Pockman, W.T.; M.D. Smith; Alan K. Knapp; Luo, Y. (Biogeosciences, 2014)
Extremes in climate may severely impact ecosystem structure and function, with both the magnitude and rate of response differing among ecosystem types and processes. We conducted a modeling analysis of the effects of extreme drought on two key ecosystem processes, production and respiration, and, to provide a broader context, we complemented this with a synthesis of published results that cover a wide variety of ecosystems. The synthesis indicated that across a broad range of biomes, gross primary production (GPP) was generally more sensitive to extreme drought (defined as proportional reduction relative to average rainfall periods) than was ecosystem respiration (ER). Furthermore, this differential sensitivity between production and respiration increased as drought severity increased; it occurred only in grassland ecosystems, and not in evergreen needle-leaf and broad-leaf forests or woody savannahs. The modeling analysis was designed to enable a better understanding of the mechanisms underlying this pattern, and focused on four grassland sites arrayed across the Great Plains, USA. Model results consistently showed that net primary productivity (NPP) was reduced more than heterotrophic respiration (Rh) by extreme drought (i.e., 67% reduction in annual ambient rainfall) at all four study sites. The sensitivity of NPP to drought was directly attributable to rainfall amount, whereas the sensitivity of Rh to drought was driven by soil drying, reduced carbon (C) input and a drought-induced reduction in soil C content – a much slower process. However, differences in reductions in NPP and Rh diminished as extreme drought continued, due to a gradual decline in the soil C pool leading to further reductions in Rh. We also varied the way in which drought was imposed in the modeling analysis; it was either imposed by simulating reductions in rainfall event size (ESR) or by reducing rainfall event number (REN). Modeled NPP and Rh decreased more by ESR than REN at the two relatively mesic sites but less so at the two xeric sites. Our findings suggest that responses of production and respiration differ in magnitude, occur on different timescales, and are affected by different mechanisms under extreme, prolonged drought.

Direct and indirect relationships between genetic diversity of a dominant grass, community diversity and above-ground productivity in tallgrass prairie - Chang, C.C.; M.D. Smith (Journal of Vegetation Science, 2014)
Question Both genetic diversity within a dominant species and species diversity have been shown to affect productivity. However, these two levels of diversity have the potential to affect productivity in similar or opposing ways. Our study assessed direct and indirect relationships between genetic diversity of a dominant grass species and plant community diversity on productivity within a mesic grassland with naturally co-occurring genotypes and species. Location Konza Prairie Biological Station, Kansas, USA (39°05′35″ N, 96°33′31″ W). Methods We conducted a study at two sites (~65 plots per site) in intact tallgrass prairie that have been subjected to frequent (burned 14 times) and infrequent (burned nine times) fire treatments for ~30 yrs. With frequent burning, the dominant C4 grass, Andropogon gerardii, typically has higher abundance; in contrast, infrequently burned sites typically have higher species diversity but lower abundance of A. gerardii. Therefore, we hypothesized that genetic diversity within A. gerardii would have a significant direct relationship with productivity for the frequently burned site due to higher population abundances of A. gerardii overall, whereas species diversity would have a significant direct relationship with productivity for the infrequently burned site. Results Contrary to our predictions, genetic diversity of A. gerardii was not related to above-ground productivity either directly or indirectly via traits, while diversity at the community level had a negative indirect relationship with productivity via a negative effect of A. gerardii abundance on community diversity for both frequently and infrequently burned sites. Conclusions While much of the focus of diversity–productivity research has been on direct relationships between diversity at the community or population level separately, future studies should examine the indirect and potentially interactive effects of both levels of diversity in natural communities.
Keywords: Community diversity; disturbance; dominant species; Fire; Grassland; Phylogenetic diversity; Plant trait; Productivity–diversity relationship; Structural equation modelling

Ecological consequences of shifting the timing of burning tallgrass prairie - Towne, E.G.; Craine, J.M. (PLOS One, 2014)
In the Kansas Flint Hills, grassland burning is conducted during a relatively narrow window because management recommendations for the past 40 years have been to burn only in late spring. Widespread prescribed burning within this restricted time frame frequently creates smoke management issues downwind. A potential remedy for the concentrated smoke production in late spring is to expand burning to times earlier in the year. Yet, previous research suggested that burning in winter or early spring reduces plant productivity and cattle weight gain while increasing the proportion of undesirable plant species. In order to better understand the ecological consequences of burning at different times of the year, plant production and species abundance were measured for 20 years on ungrazed watersheds burned annually in autumn, winter, or spring. We found that there were no significant differences in total grass production among the burns on either upland or lowland topographic positions, although spring burned watersheds had higher grass culm production and lower forb biomass than autumn and winter burned watersheds. Burning in autumn or winter broadened the window of grass productivity response to precipitation, which reduces susceptibility to mid-season drought. Burning in autumn or winter also increased the phenological range of species by promoting cool-season graminoids without a concomitant decrease in warm-season grasses, potentially widening the seasonal window of high-quality forage. Incorporating autumn and winter burns into the overall portfolio of tallgrass prairie management should increase the flexibility in managing grasslands, promote biodiversity, and minimize air quality issues caused by en masse late-spring burning with little negative consequences for cattle production.

Ecological implications of grass bud bank and tiller dynamics in mixed-grass prairie - Ott, J.P. (Kansas State University, 2014)
Perennial grass populations propagate vegetatively via the belowground bud bank. Climate, photosynthetic pathway, and growth form impact bud production, longevity, and dormancy; leading to alterations in bud bank and tiller dynamics. Previous research in mesic C₄-dominated tallgrass prairie revealed that a C₄ grass had greater bud longevity and differing bud bank dynamics than a C₃ species. This study examined the bud bank dynamics of rhizomatous and caespitose grasses in a more arid C₃ dominated prairie to gain insights into how bud banks differ among grass species, growth forms, and environments, and the relationship between bud bank characteristics and grass architecture and growth patterns. The bud bank and tiller dynamics of four perennial grasses in the C₃-dominated northern mixed grass prairie were examined over 15 months. The C₃ caespitose and rhizomatous grasses produced similar numbers of buds per tiller and their bud longevity was [greater than or equal to] 2 years. Tiller longevity drove the turnover within the bud bank of the dominant C₃ caespitose grasses Hesperostipa comata and Nassella viridula. Their polycyclic tillers (tillers that lived for more than one year) created multi-aged bud banks. The rhizomatous C₃ grass Pascopyrum smithii also had a multi-aged bud bank because buds were able to live longer than its annual tillers. Differences between caespitose and rhizomatous C₃ grass bud banks were driven by differences in tiller and rhizome production and spatial distribution. Responses to water availability fluctuations are likely buffered by the maintenance of polycyclic tillers in the caespitose grasses and flexible timing of annual tiller recruitment in the rhizomatous grass. The C₄ rhizomatous grass Andropogon gerardii had similar phenology to populations in its tallgrass prairie range center. Despite declines in bud production per tiller and lowered flowering probability in mixed-grass prairie, A. gerardii maintained a multi-aged bud bank and a positive population growth rate via vegetative reproduction at both the center and edge of its range. Bud bank dynamics of different growth forms and photosynthetic pathways, as they offer insight into the control of grass population dynamics and production, will enhance understanding of the mechanisms by which management practices and environmental change can alter perennial grasslands.
Keywords: Bud bank; Grass; Mixed-grass prairie; perennial grass; Tiller dynamics; Vegetative reproduction

Ecological thresholds and abrupt transitions of tallgrass prairie to shrublands and woodlands - Z. Ratajczak (Kansas State University, 2014)
Ecological thresholds are breakpoints where small increases in external pressure can generate rapid and difficult to reverse ecological transitions. Often, ecological thresholds are not recognized until they are crossed at a large-scale, leading to unintended and lasting externalities. In tallgrass prairie, we identified ecological thresholds of 3-year fire returns and ~60% grass cover, based on mechanistic field studies and long-term fire and grazing experiments. When tallgrass prairie is pushed passed these thresholds, it makes an abrupt transition to a self-reinforcing shrubland state. Demographic bottlenecks, niche partitioning, and altered fire feedback mechanisms account for both the non-linear nature of grassland-shrubland transitions and the resistance of established shrublands to fire and drought. In the last decade, only ~27% of Central Great Plains tallgrass prairie was burned every 1-2 years, and therefore ~73% of this region is susceptible to shrubland and woodland transitions in the next two to three decades. If transitions to shrublands and woodlands do occur, we expect a multi-trophic loss of grassland biodiversity, decreased cattle production, and the potential for damaging woodland fires in close proximity to human development. However, knowledge of fire thresholds, adaptive management tools, and bottom-up citizen action campaigns are creating a rare window of opportunity to avoid transformation of the remaining tallgrass prairies.

Estimating canopy nitrogen content in a heterogeneous grassland with varying fire and grazing treatments: Konza Prairie, Kansas, USA - Ling, B.H.; Goodin, D.G.; Mohler, R.L.; Laws, A.N.; Anthony Joern (Remote Sensing, 2014)
Quantitative, spatially explicit estimates of canopy nitrogen are essential for understanding the structure and function of natural and managed ecosystems. Methods for extracting nitrogen estimates via hyperspectral remote sensing have been an active area of research. Much of this research has been conducted either in the laboratory, or in relatively uniform canopies such as crops. Efforts to assess the feasibility of the use of hyperspectral analysis in heterogeneous canopies with diverse plant species and canopy structures have been less extensive. In this study, we use in situ and aircraft hyperspectral data to assess several empirical methods for extracting canopy nitrogen from a tallgrass prairie with varying fire and grazing treatments. The remote sensing data were collected four times between May and September in 2011, and were then coupled with the field-measured leaf nitrogen levels for empirical modeling of canopy nitrogen content based on first derivatives, continuum-removed reflectance and ratio-based indices in the 562–600 nm range. Results indicated that the best-performing model type varied between in situ and aircraft data in different months. However, models from the pooled samples over the growing season with acceptable accuracy suggested that these methods are robust with respect to canopy heterogeneity across spatial and temporal scales.
Keywords: heterogeneous canopy; hyperspectral remote sensing; nitrogen estimates

Eutrophication weakens stabilizing effects of diversity in natural grasslands - Hautier, Y.; Seabloom, E.W.; E.T. Borer; P. Adler; Harpole, W.S.; Hillebrand, H.; Lind, E.M.; MacDougall, A.S.; Stevens, C.J.; J.D. Bakker; Buckley, Y.M.; Chu, C.; et al. (Nature, 2014)
Studies of experimental grassland communities1, 2, 3, 4, 5, 6, 7 have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others1, 2. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change8, 9, 10, 11. Here we analyse diversity–stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally8. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.
Keywords: Biodiversity; Community ecology; Grassland ecology

Experimental evidence that invasive grasses use allelopathic biochemicals as a potential mechanism for invasion: Chemical warfare in nature - Greer, M.J.; G.T. Wilson; Hickman, K.R.; Wilson, S. (Plant and Soil, 2014)
Background and aims Bothriochloa spp. are non-native warm-season grasses invading native grasslands of the southern and central Great Plains, altering ecological services these grasslands supply. Our study investigated potential allelopathic effects of the invasive grass species B. ischaemum on native grass germination, growth, and survival. Methods Leachate or litter from Andropogon gerardii (native) or B. ischaemum were applied to two native grass species (A. gerardii; Schizachyrium scoparium). Leachate and litter were also added to B. ischaemum and a water control was included. Germination, above- and belowground biomass, and survival were determined. Results Application of B. ischaemum leachate or litter significantly reduced the germination, growth, and survival of both A. gerardii and S. scoparium but had no conspecific effects, while A. gerardii treatments had no effect on any species. Conclusions Bothriochloa spp. may gain a competitive advantage through allelopathic biochemicals. It is unclear if these allelopathic effects directly hinder competitors or indirectly hinder them through alterations in soil microbial communities, however, reductions in germination of native seeds strongly support direct allelopathic effects. Greater phenolic content in native grass leachates suggest allelopathic biochemical production may not be unique to non-native species and may be a mechanism for maintenance of plant species biodiversity in native systems.
Keywords: Allelopathy; Bothriochloa spp; Invasive species; Leachate; Leaf litter; Yellow bluestem

Fire and grazing influences on rates of riparian woody plant expansion along grassland streams - Veach, A.M.; W. K. Dodds; Skibbee, A. (PLOS ONE, 2014)
Grasslands are threatened globally due to the expansion of woody plants. The few remaining headwater streams within tallgrass prairies are becoming more like typical forested streams due to rapid conversion of riparian zones from grassy to wooded. Forestation can alter stream hydrology and biogeochemistry. We estimated the rate of riparian woody plant expansion within a 30 m buffer zone surrounding the stream bed across whole watersheds at Konza Prairie Biological Station over 25 years from aerial photographs. Watersheds varied with respect to experimentally-controlled fire and bison grazing. Fire frequency, presence or absence of grazing bison, and the historical presence of woody vegetation prior to the study time period (a proxy for proximity of propagule sources) were used as independent variables to predict the rate of riparian woody plant expansion between 1985 and 2010. Water yield was estimated across these years for a subset of watersheds. Riparian woody encroachment rates increased as burning became less frequent than every two years. However, a higher fire frequency (1–2 years) did not reverse riparian woody encroachment regardless of whether woody vegetation was present or not before burning regimes were initiated. Although riparian woody vegetation cover increased over time, annual total precipitation and average annual temperature were variable. So, water yield over 4 watersheds under differing burn frequencies was quite variable and with no statistically significant detected temporal trends. Overall, burning regimes with a frequency of every 1–2 years will slow the conversion of tallgrass prairie stream ecosystems to forested ones, yet over long time periods, riparian woody plant encroachment may not be prevented by fire alone, regardless of fire frequency.
Keywords: Anthrax; Bacillus anthracis; Bacterial spores; Cytokines; Edema; Immune response; Innate immune system; Lungs

Fire dynamics distinguish grasslands, shrublands, and woodlands as alternative attractors in the Central Great Plains of North America - Z. Ratajczak; Jesse B. Nippert; J. M. Briggs; John M. Blair (Journal of Ecology, 2014)
Grasslands are threatened globally due to the expansion of woody plants. The few remaining headwater streams within tallgrass prairies are becoming more like typical forested streams due to rapid conversion of riparian zones from grassy to wooded. Forestation can alter stream hydrology and biogeochemistry. We estimated the rate of riparian woody plant expansion within a 30 m buffer zone surrounding the stream bed across whole watersheds at Konza Prairie Biological Station over 25 years from aerial photographs. Watersheds varied with respect to experimentally-controlled fire and bison grazing. Fire frequency, presence or absence of grazing bison, and the historical presence of woody vegetation prior to the study time period (a proxy for proximity of propagule sources) were used as independent variables to predict the rate of riparian woody plant expansion between 1985 and 2010. Water yield was estimated across these years for a subset of watersheds. Riparian woody encroachment rates increased as burning became less frequent than every two years. However, a higher fire frequency (1–2 years) did not reverse riparian woody encroachment regardless of whether woody vegetation was present or not before burning regimes were initiated. Although riparian woody vegetation cover increased over time, annual total precipitation and average annual temperature were variable. So, water yield over 4 watersheds under differing burn frequencies was quite variable and with no statistically significant detected temporal trends. Overall, burning regimes with a frequency of every 1–2 years will slow the conversion of tallgrass prairie stream ecosystems to forested ones, yet over long time periods, riparian woody plant encroachment may not be prevented by fire alone, regardless of fire frequency.
Keywords: bison; Ecosystems; Forests; Grasslands; Grazing; Linear regression analysis; Trees; Watersheds

Fitness among population sources of a dominant species (Andropogon gerardii Vitman) used in prairie restoration - D.J. Gibson; Sendor, G.; Donatelli, J.; S.G. Baer; Johnson, L. (Torrey Botanical Society, 2014)
Planting native grasses can provide a source of seed for prairie restorations, but requires knowledge of how the plants that establish will perform. This study sought to determine variation in fitness of population sources of Andropogon gerardii, a dominant grassland species, when grown in a mesic common garden. Using multiple population sources, we tested the hypothesis that plants from populations within the local region would exhibit a ‘home-site advantage’ as measured by higher fitness compared to plants from populations collected from drier regions of the tallgrass prairie ecosystem (up to 986 km west of the common garden). Plants collected from four pristine, never restored population sources from each of three regions (central Kansas, eastern Kansas, and southern Illinois) were raised in the greenhouse from seeds and planted in a common garden in Illinois. To estimate fitness, we used commonly measured traits related to seed production, including flowering tiller number and number of flowering raceme branches, seed number, viability, and percentage germination. There was no evidence of a ‘home-site advantage’ for populations originating from southern Illinois. Rather, there was high within-region variability in fecundity. Plants from southern Illinois had the largest number of raceme branches per plant. Plants from eastern Kansas had the highest number of vegetative tillers per plant. Plants from central Kansas produced the most germinable seeds. Under the current climate, plants from any one of the three regions may be suitable to propagate seeds for restoration, but other traits may vary among populations to affect height, cover, and productivity.
Keywords: Andropogon gerardii; fitness; grassland; reproductive effort; restoration

FOAM: Functional Ontology Assignments for Metagenomes: a Hidden Markov Model (HMM) database with environmental focus - Prestat, E.; David, M.; Hultman, J.; Tas, N.; Lamendella, R.; Dvornik, J.; Mackelprang, R.; Myrold, D.D.; A. Jumpponen; Tringe, S.; Holman, E.; Mavromatis, K.; et al. (Nucleic Acids Research, 2014)
A new functional gene database, FOAM (Functional Ontology Assignments for Metagenomes), was developed to screen environmental metagenomic sequence datasets. FOAM provides a new functional ontology dedicated to classify gene functions relevant to environmental microorganisms based on Hidden Markov Models (HMMs). Sets of aligned protein sequences (i.e. ‘profiles’) were tailored to a large group of target KEGG Orthologs (KOs) from which HMMs were trained. The alignments were checked and curated to make them specific to the targeted KO. Within this process, sequence profiles were enriched with the most abundant sequences available to maximize the yield of accurate classifier models. An associated functional ontology was built to describe the functional groups and hierarchy. FOAM allows the user to select the target search space before HMM-based comparison steps and to easily organize the results into different functional categories and subcategories. FOAM is publicly available at http://portal.nersc.gov/project/m1317/FOAM/.

Geographic variation in growth and phenology of two dominant Central US grasses: Consequences for climate change - Giuliani, A.L.; Kelly, E.F.; Alan K. Knapp (Journal of Plant Ecology, 2014)
Aims The rate of climate change may exceed many plant species’ migration rates, particularly for long-lived perennial species that dominate most ecosystems. If bioclimatic envelopes shift more rapidly than dominant species can migrate, individuals located peripheral to biomes or in adjacent biomes may become a significant source of traits for future dominant populations (DPs). Thus, traits of individuals from peripheral populations (PPs) may affect future ecosystem functioning more than those of today’s DPs. Methods We assessed key traits of individuals collected from populations that currently dominate two central US grasslands, the shortgrass steppe (Bouteloua gracilis) and the tallgrass prairie (Andropogon gerardii). We compared these to individuals from PPs in a reciprocal-transplant common garden experiment with gardens at the Shortgrass Steppe Long Term Ecological Research site in Colorado and the Konza Prairie Biological Station Long Term Ecological Research site in Kansas. DPs and PPs were subjected to high and reduced water availability in common gardens located in each biome. Traits measured included the following: individual plant biomass, reproductive allocation, specific leaf area (SLA) and plant–water relations. We focused on the climate-change relevant comparisons of traits from PPs versus DPs expressed under the climate of DPs. Important Findings PPs of B. gracilis differed from DPs primarily in phenological traits. Under a semiarid shortgrass steppe climate, PPs initiated flowering later in the season, produced fewer reproductive tillers and were more sensitive to water stress. Biomass differences between populations were minimal. For A. gerardii, biomass in PPs was 50% lower than in DPs under the mesic tallgrass prairie climate and reproductive tillers were considerably smaller, despite higher SLA in PPs. Biomass of PPs was less sensitive to water stress, however. From these results, we conclude that key traits of PPs differed from DPs in both grassland types, but potential effects on reproductive phenology were greater for the bioclimatic shift in which a mesic biome becomes arid, whereas aboveground productivity may be affected more when a semiarid biome becomes more mesic.
Keywords: grassland; phenology; productivity; traits; water stress

Grassland Ecology - John M. Blair; Jesse B. Nippert; J. M. Briggs (Plant Sciences - Ecology and the Environment, 2014)

Herbivores and nutrients control grassland plant diversity via light limitation - E.T. Borer; Seabloom, E.W.; Gruner, D.S.; Harpole, W.S; Hillebrand, H.; Lind, E.M.; P. Adler; J. Alberti; Anderson, T.M.; J.D. Bakker; L.A. Biederman; D.M. Blumenthal; et al. (Nature, 2014)

How does your prairie (re)grow?: Interactions of seed additions with resource availability, heterogeneity, and disturbance on recruitment and diversity in a restored tallgrass prairie - Stanton, N.L. (Kansas State University, 2014)
Temperate grasslands are among the most threatened biomes in the world, with the largest historical losses due to conversion to agricultural land. While much of this biome has already been converted, there is concern the last remaining remnants in North America will be converted in response to increasing demand for crops used for ethanol production. Thus, restoring grasslands post-anthropogenic disturbance is increasingly important for conserving grassland biodiversity. Two major challenges for prairie restorations are establishing the many subdominant and rarer species found in native prairie, and offsetting the typical decline in richness and diversity over time as restorations age. Repeated seed addition of targeted species is commonly used to override low and declining plant richness and diversity. While this is generally effective early in restoration (i.e., as communities are establishing), its effectiveness in later stages (i.e., when established communities are often losing diversity) remains unknown. I investigated plant community responses to combinations of resource manipulations and disturbances coupled with a seed addition in a 15-yr old restored grassland to test the hypothesis that spatial resource heterogeneity increases the rate of colonization into established prairie restoration communities. Seeds were added to a long-term restoration experiment involving soil depth manipulations (deep, shallow) crossed with nutrient manipulations (reduced N, ambient N, enriched N). Seedling emergence was generally low and only 8 of the 14 forb species added were detected in the first growing season. I found no effect of increased resource heterogeneity on the abundance or richness of seedlings. There was a significant nutrient effect (p<0.1, α=0.1) on seedling abundance, with higher emergence in the enriched N than the ambient N treatment. I also found unexpected nutrient effects on richness, diversity and Mean C (Mean C = Σ CoCi*Ai, where CoC=Coefficient of Conservatism and A=relative abundance of the ith species). All values, except Mean C, were higher in the enriched N treatment than in either the reduced or ambient N treatments. Mean C was lowest in the enriched N treatment, and highest in the whole-plot control, suggesting that the majority of species contributing to higher richness and diversity in the enriched N treatment were “weedier” species. In a separate experiment, I found no effect of small-scale disturbances (aboveground biomass removal or soil disturbance) on seedling abundance or seedling richness. I did find a marginal effect of disturbance type on seedling richness (p=0.11, α=0.1), with higher seedling richness in the soil disturbance than the aboveground biomass removal treatment. I did not find any disturbance effects on community response variables. These results indicate that recruitment from seed additions into well-established restored communities is relatively low in the first year following a seed addition, regardless of resource availability and heterogeneity. Follow-up studies to determine recruitment rates in subsequent years are needed to elucidate whether recruitment responses are driven more by individual species differences or by environmental mechanisms.
Keywords: Tallgrass prairie; Ecological restoration; Resource availability and heterogeneity; Long-term; Propagule; Seedling

Impacts of seasonality and surface heterogeneity on water-use efficiency in mesic grasslands - N. Brunsell; Jesse B. Nippert; Buck, T.L. (Ecohydrology, 2014)
Woody encroachment is occurring in grasslands worldwide, with largely unknown effects on local carbon and water fluxes and the energy balance. Water-use efficiency (λ) is a measure of carbon assimilation per evapotranspiration. Here, a was compared among three different grassland ecosystems in eastern KS, USA, by using the eddy covariance technique. Variation in λ was examined at multiple timescales and across different burning regimes. Site-specific variations in λ were more readily observed at seasonal and inter-annual timescales rather than daily and monthly averages. Annually burned grassland with homogeneous C4 grass cover had less negative values of λ [lower water-use efficiency (WUE)] than infrequently burned grassland that is presently undergoing woody encroachment and a transition to a shrub-dominated ecosystem. The most likely explanation for differences in λ are differences in rooting depth and source-water acquisition between encroaching woody plants and the native grass community. Reliance on a deeper water source by the woody community may buffer the negative consequences of forecasted climate variability and drought, resulting in greater landscape WUE and reduced susceptibility to water stress when compared with the coexisting grass species. Copyright © 2013 John Wiley & Sons, Ltd.

The influence of fire and grazing on tallgrass prairie streams and herpetofauna - Larson, D. M. (Kansas State University, 2014)
Tallgrass prairie evolved with fire-grazer interactions. Fire and grazing are vital processes for maintaining grasslands and cattle production, and therefore will be continued as land management schemes. The effects of fire and grazers on prairie streams are understudied, but may significantly influence stream ecology. This dissertation examined how prescribed burning, bison grazing, and patch-burn grazing (by cattle) influence water quality, stream biota, and riparian amphibians and reptiles at Konza Prairie, Kansas, or Osage Prairie, Missouri. Using Global Positioning System, we monitored bison and cattle distribution throughout watersheds. The immediate effects of prescribed burning were examined at both Konza and Osage Prairies. The impacts of bison on water quality were determined by using a long-term dataset from Konza Prairie and compared watersheds with and without bison. Amphibian and reptile assemblages were monitored for two years at Osage, and assemblage data were analyzed using redundancy analysis, permuted analysis of variance, and occupancy modeling. A patch-burn grazing experiment occurred for 5 years at Osage (2 years pretreatment data and 3 years of treatments) and was analyzed using a before-after, control-impact design. Prescribed burning had minimal effects on water chemistry. At Konza Prairie, bison did not alter water quality likely because they spent negligible time (<5%) in streams. Contrarily, cattle at Osage Prairie significantly increased stream concentrations of total suspended solids, nutrients, Escherichia coli bacteria, algal biomass, and primary production. Unlike bison, cattle spent significant time (~21%) in streams if allowed access to riparian zones. In watersheds with cattle excluded from streams by riparian fencing, water quality contaminant concentrations increased significantly, but not to the magnitude of unfenced streams. Amphibian abundance and richness were not different among patch types; instead, they were restricted to specific basins. However, reptiles displayed preference for certain patch-types, and had the highest abundance and richness in watersheds with fire and grazing. These results have implications for natural resource management. Riparian fencing of cattle may be a useful practice in areas where water resource protection is the priority. However, overland flow may alter water quality in watersheds with grazers despite fencing. Land managers will need to define management objectives and accept trade-offs in water quality, amphibian and reptile habitat, and cattle production.
Keywords: Cattle; Bison; Amphibian; Reptile; Grasslands

Influence of watershed grazing management on stream geomorphology in grassland headwater streams - Grudzinski, Bartosz Piotr (Kansas State University, 2014)
This dissertation increases our understanding of the drivers that shape and maintain grassland streams and their watersheds by examining the influence of grazing management practices on suspended sediment concentrations, bare ground production, and changes to channel geomorphology. Chapter 2 demonstrates that cattle grazing produces significantly higher baseflow suspended sediment concentrations relative to bison grazing. Suspended sediment concentrations within bison-grazed streams are similar to ungrazed streams, indicating that the substitution of cattle for bison has resulted in degradation of baseflow water quality in grassland streams. Burning frequency, discharge, and seasonality are also significant drivers of suspended sediment concentrations, but are generally less influential than grazing treatments. Chapter 3 indicates that high density cattle grazing treatments produce more bare ground within the riparian zones of grassland stream networks, particularly underneath tree canopy cover. The increased bare ground coverage within riparian areas is correlated with increased suspended sediment concentrations during baseflow conditions, while watershed-scale bare ground production is correlated with increased suspended sediment concentrations during storm flow events. Chapter 4 demonstrates channel geometry and sedimentology are significantly influenced by grazing treatments. This dissertation is the first study to comparatively evaluate the relative influence between cattle and bison grazing on stream geomorphology within any environment. Insight gained from this project can be used by public and private land use managers to improve the environmental integrity of native grassland ecosystems.
Keywords: agriculture; ecology; Fluvial; Geomorphology; Landuse; Sediment

Inorganic and organic carbon variations in surface water, Konza Prairie LTER Site, USA, and Maolan Karst Experimental Site, China - Liu, Huan. (University of Kansas, 2014)
Two natural groundwater-fed streams were selected to examine the diurnal trends of water geochemistry, CO2 emissions, and sources of OC on 25 May 2012 at the Konza Prairie Long-Term Ecological Research (LTER) site, USA and 29 August - 30 August 2012 at the Maolan Karst Experimental (Maolan) Site, China. For the stream at the Konza LTER site, little variation in water chemistry was observed among the upstream, midstream and downstream locations, indicating the groundwater and stream water chemistry was mostly stable on a daily basis. 13CDIC was the highest at the downstream site due to the largest CO2 degassing. The autochthonous particulate organic carbon (POC) fraction at the upstream, midstream and downstream sites was 12-35%, 39-65% and 75-88%, respectively. Estimation of the C/N ratio for POC samples at the three locations was 10.4-15.0, 14.0-15.9 and 12.2-13.3. This is comparable to previously measured C/N ratios of suspended POC. For the stream at the Maolan site, there was little or no diel variation in the spring water physical and chemical parameters. However, all parameters show distinct diel changes in the spring-fed midstream pond with flourishing submerged plants. Temperature, pH, DO, SIC, 13CDIC increased during the day and decreased at night, while EC, [HCO3-], [Ca2+], and pCO2 behaved in the opposite sense. Strong aquatic photosynthesis was indicated from maximum DO values (two to three times higher than normal water equilibrated with atmospheric O2). In the downstream pond with fewer submerged plants but larger volume, all parameters displayed similar trends to the midstream pond but with much less change. We attribute this pattern to the lower biomass/water volume ratio. The diel variations in the two ponds resulted from the aquatic photosynthetic effect, demonstrating that natural surface water systems may constitute an important sink of carbon.

Interactive effects of grazing, drought, and fire on grassland plant communities in North America and South Africa - Koerner, S.E.; Scott. L. Collins (Ecology, 2014)
Grazing, fire, and climate shape mesic grassland communities. With global change altering all three factors, understanding how grasslands respond to changes in these combined drivers may aid in projecting future changes in grassland ecosystems. We manipulated rainfall and simulated grazing (clipping) in two long-term fire experiments in mesic grasslands in North America (NA) and South Africa (SA). Despite their common drivers, grasslands in NA and SA differ in evolutionary history. Therefore, we expected community structure and production in NA and SA to respond differently to fire, grazing, and drought. Specifically, we hypothesized that NA plant community composition and production would be more responsive than the SA plant communities to changes in the drivers and their interactions, and that despite this expected stability of SA grasslands, drought would be the dominant factor controlling production, but grazing would play the primary role in determining community composition at both sites. Contrary to our hypothesis, NA and SA grasslands generally responded similarly to grazing, drought, and fire. Grazing increased diversity, decreased grass cover and production, and decreased belowground biomass at both sites. Drought alone minimally impacted plant community structure, and we saw similar treatment interactions at the two sites. Drought was not the primary driver of grassland productivity, but instead drought effects were similar to or less than grazing and fire. Even though these grasslands differed in evolutionary history, they responded similarly to our fire, grazing, and climate manipulations. Overall, we found community and ecosystem convergence in NA and SA grasslands. Grazing and fire are as important as climate in controlling mesic grassland ecosystems on both continents.

Knowledge and tools to enhance resilience of beef grazing systems for sustainable animal protein production - Steiner, Jean L.; Engle, David M.; Xiao, Xiangming; Saleh, Ali; Tomlinson, Peter; C. W. Rice; Cole, N. Andy; Coleman, Samuel W.; Osei, Edward; Basara, Jeffrey; Middendorf, Gerad; Gowda, Prasanna; et al. (Annals of the New York Academy of Sciences, 2014)

Lack of eutrophication in a tallgrass prairie ecosystem over 27 years - McLauchlan, K.K.; Craine, J.M.; Jesse B. Nippert; Ocheltree, T.W. (Ecology, 2014)
Many North American grasslands are receiving atmospheric nitrogen (N) deposition at rates above what are considered critical eutrophication thresholds. Yet, potential changes in grassland function due to anthropogenic N deposition are poorly resolved, especially considering that other dynamic factors such as land use and precipitation can also affect N availability. To better understand whether elevated N deposition has altered ecosystem structure or function in North American grasslands, we analyzed a 27-year record of ecophysiological, community, and ecosystem metrics for an annually burned Kansas tallgrass prairie. Over this time, despite increasing rates of N deposition that are within the range of critical loads for grasslands, there was no evidence of eutrophication. Plant N concentrations did not increase, soil moisture did not decline, forb diversity did not decline, and the relative abundance of dominant grasses did not shift toward more eutrophic species. Neither aboveground primary productivity nor N availability to plants increased. The fates of deposited N in grasslands are still uncertain, and could include management losses through burning and grazing. However, evidence from this grassland indicates that eutrophication of North American grassland ecosystems is not an inevitable consequence of current levels of N deposition.

Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa - Eby, S.; Burkepile, D.E.; Fynn, R.W.S.; Burns, C.E.; Govender, N.; Hagenah, N.; Koerner, S.E.; Matchett, K.J.; Thompson, D.I.; K.R. Wilcox; Scott. L. Collins; Kirkman, K.P.; et al. (Oecologia, 2014)
Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.
Keywords: disturbance; fire; Grazing; Plant community richness; Species diversity

A mechanistic framework for understanding prairie stream fish distributions - Troia, M.J. (Kansas State University, 2014)
A fundamental goal of ecology is to understand environmental associations of species. These associations can provide a basis for predicting spatial distributions in contemporary habitats as well as how those distributions might change in response to anthropogenic environmental change. Developing species distribution models is limited by an incomplete understanding of functional traits, spatial scaling, and the mechanisms and generalities of correlations among abundance and environmental gradients. I address these four issues using observational and experimental approaches. First, I tested opposing mechanisms of community assembly by measuring the dispersion (i.e., diversity) of three types of functional strategies at three spatial scales and along environmental gradients. I found that communities are assembled via abiotic environmental filtering, but the strength of this filtering depends on the spatial scale of investigation, longitudinal network position, and type of functional strategy. Second, I quantified community-environment relationships across thirteen sub-basins, nested within the three major basins within Kansas to evaluate the consistency (i.e., generality) in predictive capability of environmental variables among sub-basins and across spatial extents. I found that longitudinal network position is consistently the strongest predictor of community composition among sub-basins, but in-stream and catchment predictors become stronger correlates of community composition with increasing spatial extent. Third, I used environmental niche models to quantify distributions of four pairs of congeneric cyprinids and found that species within each pair exhibited contrasting stream-size preferences. I then used field experiments to test for differences in individual-level performance between one pair of species (Pimephales notatus and P. vigilax) along a gradient of stream size. I found that adult spawn success and juvenile growth and condition increased with stream size for both species, indicating that these congeners respond similarly to abiotic gradients associated with the river continuum. I concluded that complementary distributions are a consequence of biotic interactions, differential environmental filtering evident in an unmeasured performance metric, or differential environmental filtering by an environmental factor operating at longer timescales. These studies demonstrate the context dependencies of characterizing habitat associations of stream fishes, but also reveal the general importance of stream size and associated environmental gradients in structuring stream fish communities.
Keywords: Community ecology; Environmental niche modeling; Fish ecology

Mismatched begging displays between foreign and host offspring reduce brood parasite fitness - Rivers, J. W.; M.A. Blundell; Rothstein, S. I. (Behavioral Ecology, 2014)
Obligate brood parasites must obtain food from unrelated host parents during the developmental period, and this may be especially difficult when parasitic nestlings are raised alone. Unlike specialist brood parasites, generalist brood parasites use a single begging display for a range of host species. In this study, we 1) tested whether the begging display of the generalist brown-headed cowbird (Molothrus ater) was more exaggerated than the closely related, nonparasitic red-winged blackbird (Agelaius phoeniceus) and 2) examined how begging displays were linked to food provisioning when both foreign species were raised by the Bell’s vireo (Vireo bellii), a small cowbird host. We also quantified parental provisioning to unparasitized broods containing 1–4 vireo nestlings to provide a reference provisioning curve to provide context for assessing the feeding rate to foreign offspring. We found blackbirds begged as intensely as (or more intensely than) cowbird nestlings, vireo parents provisioned both species similarly, and the amount of food provisioned to unparasitized broods increased with brood size and maintained per-capita vireo growth. However, feeding of a single foreign nestling was significantly less than that of a modal brood of 4 vireos, indicating parents fed foreign nestlings at submaximal rates. Vireos did not respond to begging of foreign nestlings in the same manner as their own offspring, and this led to significant fitness costs for foreign nestlings. We conclude that a single foreign nestling provided an inadequate stimulus for vireos, probably because of a mismatch between the begging displays of foreign and host offspring.
Keywords: Agelaius phoeniceus; begging; Bell’s vireo; brood parasitism; brown-headed cowbird; Molothrus ater; provisioning behavior; red-winged blackbird; Vireo bellii

Moving beyond mass loss: advancing understanding about the fate of decomposing leaf litter and pyrogenic organic matter in the mineral soil - Soong, J. (Colorado State University, 2014)
Leaf litter decomposition recycles the energy and nutrients fixed by plants during net primary productivity back to the soil and atmosphere from where they came. Traditionally, leaf litter decomposition studies have focused on litter mass loss rates, without consideration for where that mass ends up in the ecosystem. However, during litter decomposition by soil microbes a fraction of the litter mass lost is truly lost to the ecosystem as respired CO2, while another fraction remains in the ecosystem stored in the soil as soil organic matter (SOM). SOM is heterogeneous in composition, with various SOM pools remaining stored in the soil for time spans ranging from days to millennia depending on their biochemical and physical properties. Pyrogenic organic matter (py-OM) is the partially combusted plant residue left behind by fires, and has been found to contribute to long term SOM pools. SOM accounts for the largest terrestrial pool of carbon (C) in the global C cycle and stores nitrogen (N) and other nutrients for plant productivity. Therefore the formation of SOM during litter decomposition is critical to terrestrial C and N cycling and its feedback to global biogeochemical cycles. The focus of my dissertation is the study of leaf litter and py-OM decomposition, and quantitatively tracing how much decomposing litter and py-OM is used by soil microbes, how much is lost as CO2, and how much remains in the soil and contributes to SOM formation under different conditions. In order to best address my research questions, I first studied the methods of leaching of dissolved organic carbon (DOC) and 13C and 15N isotope labeling of plant material in the laboratory. Then, I conducted a laboratory incubation where I found that the amount of hot water extractable C and the lignocellulose index (Lignin/(lignin+cellulose)) can be used to predict DOM leaching, and the partitioning of C loss between DOC and CO2 from leaves and py-OM during decomposition. I also conducted two field studies using 13C and 15N labeled Andropogon gerardii leaf litter and py-OM to trace the fate of C and N losses during their decomposition in a fire affected tallgrass prairie, and understand the role of soil microarthropods in this process. I found that soil microarthropods increase the amount of leaf litter C that contributes to stabilized SOM formation during litter decomposition, by increasing litter inputs to the soil where they can be utilized by soil microbes. Finally, I found that frequent inputs of py-OM, rather than litter, due to annual burning of the tallgrass prairie alters the SOM formation process by removing relatively labile litter inputs to the soil and replacing it with py-OM that is unusable by soil microbes. Overall, my dissertation has focused on taking a mechanistic approach to understanding the process of litter and py-OM decomposition, and how their decomposition contributes to SOM formation and ecosystem CO2 fluxes. My results have helped to improve our understanding of terrestrial biogeochemistry, and the processes that control SOM formation during litter decomposition.

Naphthalene addition to soil surfaces: A feasible method to reduce soil micro-arthropods with negligible direct effects on soil C dynamics - Cotrufo, M.F.; Soong, J.; Vandegehuchte, M.L.; Ngryen, T.; Denef, K.; Shaw, E.A.; Sylvain, Z.A.; Tomasel, C.M.D.; Nielsen, U.N.; Wall, D.H. (Applied Soil Ecology, 2014)
Soil fauna are a key component of soil biodiversity and a driver of soil functioning. While the importance of soil fauna is well recognized, quantitative estimates of the role of soil fauna on soil biogeochemical processes, such as plant litter decomposition, are limited by methodological constraints. The addition of naphthalene, a polycyclic aromatic hydrocarbon (C10H8), to suppress soil fauna has been used for decades in decomposition experiments, but its efficacy remains questioned. In fact, we lack a rigorous field assessment of the efficacy of naphthalene additions for soil fauna suppression and potential non-target effects on the soil microbial community and carbon cycling. We added naphthalene at a high rate (477 g m−2) monthly for 23 months on the bare soil surface of a tallgrass prairie. We determined the effect of such additions on the abundance of nematodes and micro-arthropods along the soil profile to a depth of 20 cm at 11, 16 and 23 months after initiating naphthalene application. We used the variation in the natural 13C abundance of the naphthalene (δ13C – 25.5‰) as compared to the native soil (δ13C ∼ −17‰) to quantify naphthalene contribution to soil CO2 efflux and microbial biomarkers (PLFA). Naphthalene addition significantly reduced the abundance of oribatid mites (−45%), predatory mites (−52%) and springtails (−49%), but did not affect nematode abundance. The 13C abundance of a few Gram-negative (cy17:0, 18:1ω7c, 16:1ω7c), Gram-positive (a15:0, i15:0) and Actinobacteria (10Me-16:0, 10Me-18:0) PLFA markers decreased significantly in naphthalene treated plots, indicating bacterial utilization of naphthalene-derived C. Mixing models showed this contribution to be highly variable, with the highest naphthalene-C incorporation for Gram negative bacteria. Naphthalene-C was not incorporated in fungal PLFAs. This microbial utilization did not affect overall microbial abundance, community structure or activity, estimated as soil respiration. This experiment proves that naphthalene addition is a feasible method to reduce soil micro-arthropods in the field, with negligible direct effects on soil nematodes, microbial abundance and C dynamics.
Keywords: Fauna manipulation methods; Mites; Nematodes; PLFA; Springtails; Stable C isotopes

No effect of seed source on multiple aspects of ecosystem functioning during ecological restoration: cultivars compared to local ecotypes of dominant grasses - S.G. Baer; D.J. Gibson; Benscoter, A.M.; Reed, L.K.; Campbell, R.E.; Klopf, R.P.; Willand, J.E.; Wodika, B.R. (Evolutionary Applications, 2014)
Genetic principles underlie recommendations to use local seed, but a paucity of information exists on the genetic distinction and ecological consequences of using different seed sources in restorations. We established a field experiment to test whether cultivars and local ecotypes of dominant prairie grasses were genetically distinct and differentially influenced ecosystem functioning. Whole plots were assigned to cultivar and local ecotype grass sources. Three subplots within each whole plot were seeded to unique pools of subordinate species. The cultivar of the increasingly dominant grass, Sorghastrum nutans, was genetically different than the local ecotype, but genetic diversity was similar between the two sources. There were no differences in aboveground net primary production, soil carbon accrual, and net nitrogen mineralization rate in soil between the grass sources. Comparable productivity of the grass sources among the species pools for four years shows functional equivalence in terms of biomass production. Subordinate species comprised over half the aboveground productivity, which may have diluted the potential for documented trait differences between the grass sources to influence ecosystem processes. Regionally developed cultivars may be a suitable alternative to local ecotypes for restoration in fragmented landscapes with limited gene flow between natural and restored prairie and negligible recruitment by seed.
Keywords: genetic diversity; genetic structure; grassland; prairie; propagule; soil

Ontogenetic shifts, habitat USE and community structure: how fishes use and influence protected tallgrass prairie streams - Martin, E.C. (Kansas State University, 2014)
This dissertation consists of three research-based chapters which focus on habitat association of prairie stream fishes and how these fish communities influence stream ecosystem properties. Chapter one introduces important concepts used throughout the chapters, and describes my study streams. In chapter two, I identify local habitat factors associated with the diversity and density of fishes in two protected prairie watersheds. Specifically, the relative importance of habitat factors associated with fish communities were evaluated along a stream-size gradient and across multiple seasons and years. I found that species richness was positively associated with pool area and discharge. Redundancy analyses showed common prairie fish species exhibit ontogenetic habitat associations, with adults in deep and juveniles in shallow pools. Chapter 3 addresses how fish species richness in small prairie streams affects whole-stream metabolism and biomass distribution of benthic organic matter, algal and macroinvertebrates. This study was conducted by stocking experimental stream mesocosms that included pool-riffle habitats with three different communities that represent a gradient of species richness of headwater prairie streams from one to three common prairie stream fish species. I illustrated how species influence ecosystems across multiple spatial scales and found that different communities altered the distribution of algal biomass from benthic surfaces to floating mats and from pools to riffles. The objective of the fourth chapter was to quantify how two size classes of herbivorous prairie stream fish species, central stoneroller Campostoma anamolum and southern redbelly dace Chrosomus erythrogaster differentially affect stream ecosystem properties. This study was also conducted in experimental stream mesocosms, where each unit consisted of one riffle and one pool. Using ANOVAs, I found large dace were associated with longer filaments (F = 7.5, P = 0.002, df = 4) and small fishes with less benthic organic matter (F = 4.2, P = 0.02, df = 4). There was no evidence for ontogenetic shifts in diet and likely differences in energetic requirements and behavior drove the differences among treatments. My research finds that small-bodied prairie stream fishes have predictable habitat preferences and effects on stream properties are dependent on species identity, richness and size structure.
Keywords: stream ecology; Fish ecology; Ontogenetic shift; Habitat associations

Plains harvest mice in tallgrass prairie: abundance, habitat association and individual attributes - Kaufman, G.A.; D.W. Kaufman (Transactions of the Kansas Academy of Science, 2014)
The plains harvest mouse (Reithrodontomys montanus) inhabits grasslands in the Great Plains, but little is known about its ecology and natural history in native tallgrass prairie. We sampled native tallgrass prairie in spring and autumn by standard traplines on the Konza Prairie Biological Station during autumn 1981-spring 2013 and for shorter time periods in woodlands and brome fields. In addition to our long-term research, we studied small mammals on a large Prairie Grid (∼13 ha) that was trapped intensively (about every 2 weeks except in winter) during 1984–1987. Plains harvest mice (n = 39) were captured in native prairie but not in brome fields or wooded habitats. In all prairie sites, they were found to be rare (1.1 individuals/10,000 trap nights [TN]); in 14 Core Sites sampled for 32 years, abundance was higher in autumn (1.95/10,000 TN) than in spring (0.70/10,000 TN). It was not apparent that these low abundances were related to precipitation or another weather feature. On the Prairie Grid, plains harvest mice were associated with uplands and secondarily with slopes, whereas they avoided lowlands. Furthermore, they showed a positive response to conditions that are created during the first growing season following spring prescribed fires. Overall, 44% of individuals were males and this value did not differ from a 1:1 sex ratio. Non-reproductive females (8.7 g) were slightly larger than males (8.3 g); only females occupied the largest body size class (11.0–11.5 g). The smallest pregnant female weighed 9.0 g, whereas the smallest female that was lactating as evidenced by conspicuous mammae weighed 7.0 g. Pregnancies were recorded in spring, summer and autumn but not in winter; about one-third of females captured were pregnant. A juvenile (5.5 g) was captured in summer. We conclude that to understand this rare species (ca. 0.1% of the small mammal community on Konza Prairie) even studies with small sample sizes are important to elucidate the natural history and ecology of the plains harvest mouse.
Keywords: abundance; body size; fire effects; Konza Prairie; native tallgrass prairie; Reithrodontomys montanus; reproduction; sex ratio; topography

Plant community response to loss of large herbivores differs between North American and South African savanna grasslands - Koerner, S.E.; Burkepile, D.E.; Fynn, R.W.S.; Burns, C.E.; Eby, S.; Govender, N.; Hagenah, N.; Matchett, K.J.; Thompson, D.I.; K.R. Wilcox; Scott. L. Collins; Kirkman, K.P.; et al. (Ecology, 2014)
Herbivory and fire shape plant community structure in grass-dominated ecosystems, but these disturbance regimes are being altered around the world. To assess the consequences of such alterations, we excluded large herbivores for seven years from mesic savanna grasslands sites burned at different frequencies in North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). We hypothesized that the removal of a single grass-feeding herbivore from Konza would decrease plant community richness and shift community composition due to increased dominance by grasses. Similarly, we expected grass dominance to increase at Kruger when removing large herbivores, but because large herbivores are more diverse, targeting both grasses and forbs, at this study site, the changes due to herbivore removal would be muted. After seven years of large-herbivore exclusion, richness strongly decreased and community composition changed at Konza, whereas little change was evident at Kruger. We found that this divergence in response was largely due to differences in the traits and numbers of dominant grasses between the study sites rather than the predicted differences in herbivore assemblages. Thus, the diversity of large herbivores lost may be less important in determining plant community dynamics than the functional traits of the grasses that dominate mesic, disturbance-maintained savanna grasslands.

Plant-virus interactions and the agro-ecological interface - Alexander, H.M.; Mauck, K.E.; Whitfield, A.E.; Garrett, K.A.; Malmstrom, C.M. (European Journal of Plant Pathology, 2014)
As a result of human activities, an ever-increasing portion of Earth’s natural landscapes now lie adjacent to agricultural lands. This border between wild and agricultural communities represents an agro-ecological interface, which may be populated with crop plants, weeds of crop systems, and non-crop plants that vary from exotic to native in origin. Plant viruses are important components of the agro-ecological interface because of their ubiquity, dispersal by arthropod vectors, and ability to colonize both crop and wild species. Here we provide an overview of research on plant-virus dynamics across this interface and suggest three research priorities: (1) an increased effort to identify and describe plant virus diversity and distribution in its entirety across agricultural and ecological boundaries; (2) multi-scale studies of virus transmission to develop predictive power in estimating virus propagation across landscapes; and (3) quantitative evaluation of the influence of viruses on plant fitness and populations in environmental contexts beyond crop fields. We close by emphasizing that agro-ecological interfaces are dynamic, influenced by the human-mediated redistribution of plants, vectors, and viruses around the world, climate change, and the development of new crops. Consideration of virus interactions within these environmentally complex systems promises new insight into virus, plant, and vector dynamics from molecular mechanisms to ecological consequences.
Keywords: Agro-ecological interface; Crop; Plant fitness; Plant virus; Vector; Wild plant

Rainfall variability has minimal effects on grassland recovery from repeated grazing - Koerner, S.E.; Scott. L. Collins; John M. Blair; Alan K. Knapp; M.D. Smith (Journal of Vegetation Science, 2014)
Question Mesic grasslands experience a complex disturbance regime including frequent fire, grazing by large ungulates and strong inter-annual climate variability. As a result of climate change, growing season precipitation regimes are predicted to become more variable, with larger event sizes and longer dry periods resulting in more temporally dynamic soil moisture regimes. Increased climate variability is likely to interact with other disturbances, such as grazing, in grassland ecosystems. We investigated the individual and combined effects of increased rainfall variability and grazing on plant community composition, structure and function in an annually burned, native tallgrass prairie. Our overarching question was: are grazing impacts modified under a more variable precipitation regime? Location Konza Prairie, Kansas, USA. Methods Plots were established within a long-term rainfall manipulation experiment in which larger, but less frequent, rain events were imposed during the growing season without altering the total rain amount. We then simulated intense grazing pressure during one growing season by repeatedly clipping all graminoids to 5 cm and monitored recovery over 3 yr. Results Neither grazing nor rainfall treatments affected species richness; however, grazing decreased total and grass above-ground net primary production (ANPP) and increased forb ANPP relative to ungrazed plots. Grass stem density recovered from intense grazing under ambient rainfall but did not fully recover, even after 2 yr in the altered rainfall treatment. Conclusions We found that increased rainfall variability had little effect on tallgrass prairie structure and function, while grazing had large effects. Grazing and increased rainfall variability interacted to suppress grass stem density and delayed recovery relative to controls. Although stem density was reduced, individual stem size increased, resulting in no net change in ANPP. This suggests that ANPP in grazed and ungrazed North American tallgrass prairie may be relatively resilient under more temporally variable precipitation regimes.
Keywords: Annual net primary production; Climate change; Clipping; disturbance; diversity; Grass–forb interaction; Konza; Precipitation; Stem density

Resistance and resilience of a grassland ecosystem to climate extremes - D.L. Hoover; Alan K. Knapp; M.D. Smith (Ecology, 2014)
Climate change forecasts of more frequent climate extremes suggest that such events will become increasingly important drivers of future ecosystem dynamics and function. Because the rarity and unpredictability of naturally occurring climate extremes limits assessment of their ecological impacts, we experimentally imposed extreme drought and a mid-summer heat wave over two years in a central U.S. grassland. While the ecosystem was resistant to heat waves, it was not resistant to extreme drought, which reduced aboveground net primary productivity (ANPP) below the lowest level measured in this grassland in almost 30 years. This extreme reduction in ecosystem function was a consequence of reduced productivity of both C4 grasses and C3 forbs. However, the dominant forb was negatively impacted by the drought more than the dominant grass, and this led to a reordering of species abundances within the plant community. Although this change in community composition persisted post-drought, ANPP recovered completely the year after drought due to rapid demographic responses by the dominant grass, compensating for loss of the dominant forb. Overall, these results show that an extreme reduction in ecosystem function attributable to climate extremes (e.g., low resistance) does not preclude rapid ecosystem recovery. Given that dominance by a few species is characteristic of most ecosystems, knowledge of the traits of these species and their responses to climate extremes will be key for predicting future ecosystem dynamics and function.

Resource availability modulates above and belowground competitive interactions between genotypes of a dominant C4 grass - Chang, C.C.; M.D. Smith (Functional Ecology, 2014)
The well-described pattern of a few common and many rare species in plant communities (dominance-diversity curves) also has been documented within populations of dominant plant species. Understanding how these common genotypes coexist has implications for how genotype richness of a dominant species may impact community and ecosystem processes. Some studies have shown that increased genotype richness of a dominant species leads to an increase in above-ground productivity, suggesting niche complementarity between genotypes. However, mechanistic understanding of how genotypes may complement one another is lacking. We conducted a pairwise competition experiment between four common and naturally co-occurring genotypes of a dominant C4 grass species, Andropogon gerardii, in tallgrass prairie of the central United States. The genotypes were grown under both intra- and intergenotypic competition with different combinations of resources (low and high light, water, and nitrogen) in the greenhouse. We determined that there were above- and below-ground phenotypic differences between genotypes which results in altered competitive interactions depending on resource conditions. Different genotypes were competitively dominant under low- and high-light conditions and low and high N and water availability. Moreover, relative yield total values (RYT) for each genotype pairwise combination indicated that all four genotypes make demands on different resources, providing evidence for niche complementarity. Finally, we found that differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success of the genotypes, which has implications for the population dynamics of this primarily asexually reproducing perennial grass. Our results suggest that naturally co-occurring genotypes coexist because they are competitively dominant under different environmental conditions, providing insight into how genetic diversity within dominant plant species is maintained and may potentially affect important ecosystem processes.

Responses to fire differ between South African and North American grassland communities - Kirkman, K.; Scott. L. Collins; M.D. Smith; Alan K. Knapp; Burkepile, D.E.; Burns, C.E.; Fynn, R.W.S.; Hagenah, N.; Koerner, S.E.; Matchett, K.J.; Thompson, D.I.; K.R. Wilcox; et al. (Journal of Vegetation Science, 2014)
Question Does fire frequency affect mesic grassland plant community structure and composition similarly in North America and South Africa? Location Konza Prairie Biological Station (KNZ), Kansas, USA, and Ukulinga Research Farm (URF), KwaZulu-Natal, South Africa. Methods Plant community structure and composition were compared among annually burned, unburned and intermediate treatments within two long-term fire frequency manipulation experiments in native grasslands in North America and South Africa using comparable methodology over a 5-yr period. Because fire may reduce soil nitrogen (N) availability and thus affect plant community structure, N additions were superimposed on the fire treatments as a means of assessing direct vs indirect mechanisms driving responses to fire. Results The total number of species was higher at URF (183) than at KNZ (57). Overall divergence in plant community response to fire frequency occurred despite similar responses to nutrient additions. At KNZ, more frequent fire resulted in dominance by a few, tall, deep-rooted rhizomatous grasses (e.g. Andropogon gerardii). On unburned sites, shorter, more shade-tolerant species such as Poa pratensis increased in abundance, although A. gerardii remained dominant. Species richness increased with decreasing fire frequency at KNZ. At URF, frequent fire resulted in short, diverse grassland weakly dominated by a range of grass species, including Themeda triandra, Tristachya leucothrix and Hyparrhenia hirta. Decreasing fire frequency reduced species richness and resulted in dominance by a few, relatively tall caespitose grasses such as Aristida junciformis. There was a complete turnover of dominant species between annually burned and unburned treatments at URF, while at KNZ A. gerardii and Sorghastrum nutans occurred across the range of treatments. N addition reduced species richness in both sites. Conclusions Different responses to fire frequency between KNZ and URF are likely linked to the dominant species and their characteristic traits, including height and method of clonal reproduction, with the rhizomatous growth form of A. gerardii dominating the North American grassland. South Africa does not have an equivalent grass species; instead, a range of tufted, non-rhizomatous species dominate across the fire frequency treatments at URF. Reductions in soil N due to frequent fire did not appear to be a common mechanism driving responses in community composition in these two grasslands.
Keywords: Community ecology; Divergence; Fire frequency; Konza Prairie Biological Station; Mesic grassland; nitrogen; Nutrient addition; Richness; tallgrass prairie; Ukulinga Research Farm

Restoration ecology: introduction in a “timely” manner - Greer, M.J.; G.T. Wilson (Bulletin of the Ecological Society of America, 2014)

The role of deer browsing on plant community development and ecosystem functioning during tallgrass prairie restoration - Harris, P.T. (Southern Illinois University, 2014)
Tallgrass prairie in North America has been highly reduced and degraded by human activity (e.g. agriculture) and now human facilitated restoration is necessary to preserve and reestablish the biodiversity, structure and function of this system. In historical tallgrass prairie large ungulates (e.g. Bison bison) were keystone species that regulated many ecosystem properties and functions. Today, restored prairie often lacks these historical ungulates and white-tailed deer (Odocoileus virginianus) have largely assumed the role of dominant ungulates in small, tallgrass prairie restorations. Little is known about how white-tailed deer affect the development of plant communities and ecosystem function during the onset of prairie restoration. In June 2012 an agricultural field was restored to native prairie species in Konza Prairie Biological Station (KPBS) near Manhattan, KS. Immediately following seeding, experimental plots were established and fences were constructed in half of the plots to excluded white-tailed deer. From 2012 to 2013 deer browse of forbs, aboveground biomass (total, sown forbs, sown grasses, volunteer forbs and volunteer grasses), light availability at the soil surface, soil nutrients, and plant community composition were measure inside and outside of exclosures. The first year of this study occurred during a severe drought which diminished in year two, presenting the opportunity to examine the interaction of climate and deer browse on restoration. In plots where deer had access, the percentage of forbs browsed ranged from 1.3 to 10.5%. The effect of deer browsing on aboveground biomass varied across years for each category of biomass. Total biomass appeared to be regulated more strongly by deer than climate, as unbrowsed plots produced similar biomass in each year despite major climatic variation, while browsed plots did not follow this trend. Across all sampling periods, deer browsing increased light availability by 20%. In year two inorganic N was 19% lower in browsed plots, though potential net N mineralization did not vary between treatments. Plant communities were significantly different between years and, between browsed and unbrowsed plots as time and browsing affected community composition, diversity and richness. Deer browsing increased diversity and richness by 24% and 22% respectively. Community composition was most greatly affected by browsing in year one corresponding to the highest rates of browsing and greatest differences in aboveground biomass. These results indicate that deer can have substantial effects on the initial establishment of prairie communities as well as resource availability from the onset of restoration.
Keywords: Ecology; Conservation biology; Plant biology; range management

Soil animal responses to moisture availability are largely scale, not ecosystem dependent: Insight from a cross-site study - Sylvain, Z.A.; Wall, D.H; Cherwin, K.L; Peters, D.P.C; Reichmann, L.G; Sala, O.E. (Global Change Biology, 2014)
Climate change will result in reduced soil water availability in much of the world either due to changes in precipitation or increased temperature and evapotranspiration. How communities of mites and nematodes may respond to changes in moisture availability is not well known, yet these organisms play important roles in decomposition and nutrient cycling processes. We determined how communities of these organisms respond to changes in moisture availability and whether common patterns occur along fine-scale gradients of soil moisture within four individual ecosystem types (mesic, xeric and arid grasslands and a polar desert) located in the western United States and Antarctica, as well as across a cross-ecosystem moisture gradient (CEMG) of all four ecosystems considered together. An elevation transect of three sampling plots was monitored within each ecosystem and soil samples were collected from these plots and from existing experimental precipitation manipulations within each ecosystem once in fall of 2009 and three times each in 2010 and 2011. Mites and nematodes were sorted to trophic groups and analyzed to determine community responses to changes in soil moisture availability. We found that while both mites and nematodes increased with available soil moisture across the CEMG, within individual ecosystems, increases in soil moisture resulted in decreases to nematode communities at all but the arid grassland ecosystem; mites showed no responses at any ecosystem. In addition, we found changes in proportional abundances of mite and nematode trophic groups as soil moisture increased within individual ecosystems, which may result in shifts within soil food webs with important consequences for ecosystem functioning. We suggest that communities of soil animals at local scales may respond predictably to changes in moisture availability regardless of ecosystem type but that additional factors, such as climate variability, vegetation composition, and soil properties may influence this relationship over larger scales.

Stomatal responses to changes in vapor pressure deficit reflect tissue-specific differences in hydraulic conductance - Ocheltree, T.W.; Jesse B. Nippert; Prasad, P.V.V. (Plant, Cell and Environment, 2014)
The vapor pressure deficit (D) of the atmosphere can negatively affect plant growth as plants reduce stomatal conductance to water vapor (gwv) in response to increasing D, limiting the ability of plants to assimilate carbon. The sensitivity of gwv to changes in D varies among species and has been correlated with the hydraulic conductance of leaves (Kleaf), but the hydraulic conductance of other tissues has also been implicated in plant responses to changing D. Among the 19 grass species, we found that Kleaf was correlated with the hydraulic conductance of large longitudinal veins (Klv, r2 = 0.81), but was not related to Kroot (r2 = 0.01). Stomatal sensitivity to D was correlated with Kleaf relative to total leaf area (r2 = 0.50), and did not differ between C3 and C4 species. Transpiration (E) increased in response to D, but 8 of the 19 plants showed a decline in E at high D, indicative of an ‘apparent feedforward’ response. For these individuals, E began to decline at lower values of D in plants with low Kroot (r2 = 0.72). These results show the significance of both leaf and root hydraulic conductance as drivers of plant responses to evaporative demand.

Tallgrass prairie soil fungal communities are resilient to climate change - A. Jumpponen; Jones, K.L. (Fungal Ecology, 2014)
Climate models for central United States predict increasing temperatures and greater variability in precipitation. Combined, these shifts in environmental conditions impact many ecosystem properties and services. Long-term climate change experiments, such as the Rainfall Manipulation Plots (RaMPs), can be used to address soil community responses to simultaneous manipulation of temperature and temporal variability in precipitation. The RaMPs experiment is located in a native tallgrass prairie at the Konza Prairie Biological Station and has been operational since 1998 providing the potential to address responses to long-term environmental manipulations. To test whether community composition, richness, or diversity respond to environmental change, more than 40 000 fungal amplicons were analyzed from soil samples collected in 2006. The data suggest that soil fungal communities are compositionally resilient to predicted environmental change. This is the case both for the community composition overall as inferred from ordination analyses as well as analyses of variance for each of the most common Operational Taxonomic Units (OTUs). However, while this study suggests compositional resilience, further studies are required to address functional attributes of these communities and their responses to environmental manipulations.
Keywords: Altered precipitation; Global warming; Soil fungi; tallgrass prairie

The timing of growing season drought and its effects on above- and bekowground production in a mesic grassland - Denton, E. (Colorado State University, 2014)

Towards a mechanistic understanding of fish species niche divergence along a river continuum - Troia, M.J.; K. B. Gido (Ecosphere, 2014)
Environmental niche modeling is a valuable tool but it often fails to identify causal links between environmental gradients and individual- or population-level performance that drive species' distributions. Correlation between the abundances of stream fish species and longitudinal position in stream networks is well documented and is hypothesized to occur through differential environmental filtering of trophic traits. Still, trophically similar congeners often exhibit complementary distributions along stream size gradients, suggesting that other mechanisms are important. We present niche models to test the hypothesis that four congeneric pairs (Teleostei: Cyprinidae) exhibit complementary distributions along a gradient of stream size in the central Great Plains of Kansas, USA. Stream size was the strongest predictor of abundance compared to five other environmental variables tested and three of the four species pairs exhibited complementary distributions along a stream size gradient. We carried out field experiments to quantify potentially causal environmental gradients (food resources, temperature, and turbidity) and four measures of individual performance (adult spawning success and juvenile survival, condition, and growth) along a stream size gradient for one congeneric pair: Pimephales notatus, a tributary species and P. vigilax, a river mainstem species. These experiments revealed an increase in temperature and food resources with stream size, along with a corresponding increase in adult spawning success, juvenile condition, and juvenile growth for both species. We conclude that these congeners respond similarly to abiotic gradients associated with the river continuum and that complementary distributions are a consequence of biotic interactions, differential environmental filtering evident in an unmeasured performance metric, or differential environmental filtering by a direct environmental gradient operating at longer timescales.

Unraveling the dark septate endophyte functions: insights from the Arabidopsis model - Mandyam, K.G.; A. Jumpponen (Advances in Endophytic Research, 2014)
The global occurrence of plant root-associated fungal endophytes and their great abundance in many habitats necessitate studies to decipher their potential functions. Improved understanding of the basic endophyte ecology including host range, host preference, and host responses to endophyte colonization has been made possible through populations of endophytes (e.g., Periconia macrospinosa and Microdochium sp.) isolated from North American native tallgrass prairie. The recent demonstration of the endophyte symbiosis of the model plant Arabidopsis thaliana has provided additional tools to further elucidate the ecology of these endophytes. The availability of a large number of Arabidopsis ecotypes and mutants, microarrays, and databases allows the molecular dissection of endophyte symbiosis to better understand the importance of fungal endophytes in host nutrient uptake, defenses, and/or responses to pathogens and stress. In this chapter, we discuss the ecology and functions of endophytic fungi through experiments utilizing the Arabidopsis model system. We draw parallels with another deeply dissected Piriformospora indica root endophyte symbiosis, which has been demonstrated to promote growth of model and non-model plants.

Visual display in Blanchard's cricket frogs (Acris blanchardi) - Horne, E.A.; Foulks, S.; Bello, N.M. (The Southwestern Naturalist, 2014)
Most reports of anuran visual displays (especially those involving extension of the back legs) are of tropical species living within noisy habitats. Here, we provide a descriptive report of visual displays involving back leg extension in a temperate anuran, Blanchard's cricket frog (Acris blanchardi). We observed male cricket frogs engaging in bouts of display, lasting an average of 2.9 min and incorporating both visual and acoustic signals. In a typical display bout, frogs near each other began circling (during a chorus at the pond) within a small area while extending their back legs and occasionally vocalizing. Rarely, the frogs would attack one another by hopping onto, then off, an opponent. Bouts ended when individuals stopped displaying while remaining near each other. The most common behaviors observed during a display bout, in order of decreasing frequency, were leg extensions, direction changes, forward movements, and vocalizations. These observations increase prospects for the study of evolution of visual displays in anurans occupying relatively open, quiet habitats.

Woodland voles captured among sparse shrubs in native tallgrass prairie on Konza Prairie Biological Station, Kansas - D.W. Kaufman; Kaufman, G.A. (Transactions of Kansas Academy of Science, 2014)
From autumn 1981 through spring 2009, woodland voles (Microtus pinetorum) were captured rarely and only in woodland habitats (four in ca. 15,000 trap nights) and never in grassland habitats (ca. 300,000 trap nights) on the Konza Prairie Biological Station, Kansas. Konza Prairie is located in the Flint Hills region of eastern Kansas in Geary and Riley counties (see Knapp and Seastedt 1998 or http://keep.konza.ksu.edu/visit/map.htm for maps and location). We summarized characteristics of these voles (all four voles captured in moist gallery forest; Kaufman and Kaufman 2009) as well as their locations and habitat features because small mammals only were to be sampled in grassland sites away from gallery forest habitats as we completed our long-term studies of small mammals during autumn 2009 through spring 2013 (nearly 30,000 more trap nights during this time period). Unexpectedly, two woodland voles were captured in a prairie site during March 2013, which was the last sampling period of our 32 year study. Herein, we describe the characteristics of the two voles captured along a prairie trapline plus features of the habitat surrounding capture locations.

You are not always what we think you eat: selective assimilation across multiple whole-stream isotopic tracer studies - W. K. Dodds; Scott. L. Collins; Hamilton, S.K.; Tank, J.L.; Johnson, S.; Webster, J.R.; Simon, K.S.; M.R. Whiles; Rantala, H.M.; W.H. McDowell; Peterson, S.D.; Riis, T.; et al. (Ecology, 2014)
Analyses of 21 15N stable isotope tracer experiments, designed to examine food web dynamics in streams around the world, indicated that the isotopic composition of food resources assimilated by primary consumers (mostly invertebrates) poorly reflected the presumed food sources. Modeling indicated that consumers assimilated only 33–50% of the N available in sampled food sources such as decomposing leaves, epilithon, and fine particulate detritus over feeding periods of weeks or more. Thus, common methods of sampling food sources consumed by animals in streams do not sufficiently reflect the pool of N they assimilate. Isotope tracer studies, combined with modeling and food separation techniques, can improve estimation of N pools in food sources that are assimilated by consumers. Food web studies that use putative food samples composed of actively cycling (more readily assimilable) and refractory (less assimilable) N fractions may draw erroneous conclusions about diets, N turnover, and trophic linkages of consumers. By extension, food web studies using stoichiometric or natural abundance approaches that rely on an accurate description of food-source composition could result in errors when an actively cycling pool that is only a fraction of the N pool in sampled food resources is not accounted for.

Adoption and utility of an Arabidopsis model to dissect endophyte symbioses - A. Jumpponen; Mandyam, K.G. (Endophytes in plant protection: the state of the art, 2013)
Despite the abundance of root-associated endophytic fungi, their function has remained elusive. During experiments to determine the host ranges of common endophytes isolated from a tallgrass prairie, at least two taxa (Microdocchium and Periconia) were observed to form functional mutualisms with Arabidopsis thaliana and increase the host’s growth. Furthermore, these endophytes reduce A. thaliana susceptibility to a foliar pathogen suggesting induction of systemic plant defenses. Arabidopsis thaliana does not associate with mycorrhizal fungi and there are only limited examples of endophyte associations in A. thaliana. Accordingly, we have taken advantage of this unique and fortuitous mutualism to further our understanding of the root-associated symbioses. We argue that this system is broadly applicable and the wealth of information available for A. thaliana will allow advances in understanding mycorrhizal and non-mycorrhizal root symbioses alike. Data from unpublished and ongoing microarray (Affymetrix ATH1) experiments indicate that endophytes lead to upregulation of carbon metabolism as well as general plant defenses against potentially pathogenic fungi. Furthermore, metabolome level experiments indicate clear shifts on metabolic profiles. Together, these data indicate that both host transcriptome and metabolome are modulated by the endophyte symbionts.

Altered precipitation regime affects the function and composition of soil microbial communities on multiple time scales - Lydia H. Zeglin; Bottomley, P.J.; A. Jumpponen; C. W. Rice; Arango, M.; Lindsley, A.; McGowan, A.; Mfombep, P.; Myrold, D.D. (Ecology, 2013)
Climate change models predict that future precipitation patterns will entail lower-frequency but larger rainfall events, increasing the duration of dry soil conditions. Resulting shifts in microbial C cycling activity could affect soil C storage. Further, microbial response to rainfall events may be constrained by the physiological or nutrient limitation stress of extended drought periods; thus seasonal or multiannual precipitation regimes may influence microbial activity following soil wet-up. We quantified rainfall-driven dynamics of microbial processes that affect soil C loss and retention, and microbial community composition, in soils from a long-term (14-year) field experiment contrasting “Ambient” and “Altered” (extended intervals between rainfalls) precipitation regimes. We collected soil before, the day following, and five days following 2.5-cm rainfall events during both moist and dry periods (June and September 2011; soil water potential = −0.01 and −0.83 MPa, respectively), and measured microbial respiration, microbial biomass, organic matter decomposition potential (extracellular enzyme activities), and microbial community composition (phospholipid fatty acids). The equivalent rainfall events caused equivalent microbial respiration responses in both treatments. In contrast, microbial biomass was higher and increased after rainfall in the Altered treatment soils only, thus microbial C use efficiency (CUE) was higher in Altered than Ambient treatments (0.70 ± 0.03 > 0.46 ± 0.10). CUE was also higher in dry (September) soils. C-acquiring enzyme activities (β-glucosidase, cellobiohydrolase, and phenol oxidase) increased after rainfall in moist (June), but not dry (September) soils. Both microbial biomass C:N ratios and fungal : bacterial ratios were higher at lower soil water contents, suggesting a functional and/or population-level shift in the microbiota at low soil water contents, and microbial community composition also differed following wet-up and between seasons and treatments. Overall, microbial activity may directly (C respiration) and indirectly (enzyme potential) reduce soil organic matter pools less in drier soils, and soil C sequestration potential (CUE) may be higher in soils with a history of extended dry periods between rainfall events. The implications include that soil C loss may be reduced or compensated for via different mechanisms at varying time scales, and that microbial taxa with better stress tolerance or growth efficiency may be associated with these functional shifts.

Arabidopsis thaliana model system reveals a continuum of responses to root endophyte colonization - Mandyam, K.G.; Roe, J.; A. Jumpponen (Fungal Biology, 2013)
We surveyed the non-mycorrhizal model plant Arabidopsis thaliana microscopically for its ability to form dark septate endophyte (DSE) symbioses in field, greenhouse, and laboratory studies. The laboratory studies were also used to estimate host growth responses to 34 Periconia macrospinosa and four Microdochium sp. isolates. Consistent with broad host range observed in previous experiments, field-, greenhouse-, and laboratory-grown A. thaliana were colonized by melanized inter- and intracellular hyphae and microsclerotia or chlamydospores indicative of DSE symbiosis. Host responses to colonization were variable and depended on the host ecotype. On average, two A. thaliana accessions (Col-0 and Cvi-0) responded negatively, whereas one (Kin-1) was unresponsive, a conclusion consistent with our previous analyses with forbs native to the field site where the fungi originate. Despite the average negative responses, examples of positive responses were also observed, a conclusion also congruent with earlier studies. Our results suggest that A. thaliana has potential as a model for more detailed dissection of the DSE symbiosis. Furthermore, our data suggest that host responses are controlled by variability in the host and endophyte genotypes.
Keywords: Dark septate endophytes (DSE); Microdochium sp.; Mutualism–parasitism continuum; Periconia macrospinosa