@article {KNZ00740,
	title = {Patterns and determinants of potential carbon gain in the C3 evergreen Yucca glauca (Liliaceae) in a C4 grassland},
	journal = {American Journal of Botany},
	volume = {87},
	year = {2000},
	pages = {230 -236},
	abstract = {Yucca glauca is a C3 evergreen rosette species locally common in the C4-dominated grasslands of the central Great Plains. Most congeners of Y. glauca are found in deserts, and Y. glauca{\textquoteright}s morphological similarities to desert species (steeply angled leaves, evergreen habit) may be critical to its success in grasslands. We hypothesized that the evergreen habit of Y. glauca, coupled with its ability to remain physiologically active at cool temperatures, would allow this species to gain a substantial portion of its annual carbon budget when the C4 grasses are dormant. Leaf-level gas exchange was measured over an 18-mo period at Konza Prairie in northeast Kansas to assess the annual pattern of potential C gain. Two short-term experiments also were conducted in which nighttime temperatures were manipulated to assess the cold tolerance of this species. The annual pattern of C gain in Y. glauca was bimodal, with a spring productive period (maximum monthly photosynthetic rate = 21.1 {\textpm} 1.97 μmol{\textperiodcentered}m-2{\textperiodcentered}s-1) in March through June, a period of midseason photosynthetic depression, and a fall productive period in October (15.6 {\textpm} 1.25 μmol{\textperiodcentered}m-2{\textperiodcentered}s-1). The steeply angled leaves resulted in interception of photon flux density at levels above photosynthetic saturation throughout the year. Reduced photosynthetic rates in the summer may have been caused by low soil moisture, but temperature was strongly related (r2 = 0.37) to annual variations in photosynthesis, with nocturnal air temperatures below -5{\textdegree}C in the late fall and early spring, and high air temperatures (>32{\textdegree}C) in the summer, limiting gas exchange. Overall, 31\% of the potential annual carbon gain in Y. glauca occurred outside the {\textquotedblleft}frost-free{\textquotedblright} period (April{\textendash}October) at Konza Prairie and 43\% occurred when the dominant C4 grasses were dormant. Future climates that include warmer minimum temperatures in the spring and fall may enhance the success of Y. glauca relative to the C4 dominants in these grasslands.},
	keywords = {LTER-KNZ, Climate change, cold tolerance, evergreen, Grasslands, Liliaceae, photosynthesis, tallgrass prairie, Water relations, Yucca},
	url = {http://www.amjbot.org/content/87/2/230.short},
	author = {Maragni, L.A. and Alan K. Knapp and McAllister, C.A.}
}
@article {KNZ00696,
	title = {Elevated CO2 and leaf longevity in the C4 grassland dominant Andropogon gerardii},
	journal = {International Journal of Plant Sciences},
	volume = {160},
	year = {1999},
	pages = {1057 -1061},
	abstract = {In central U.S. grasslands, plant and ecosystem responses to elevated CO2 are most pronounced when water availability is limited. In a northeast Kansas grassland, responses to elevated CO2 in leaf area, number, development, and longevity were quantified for the tallgrass prairie dominant, Andropogon gerardii. Plants were grown in open-top chambers (OTCs) modified to limit water availability and to maximize responses to elevated CO2. In OTCs with elevated ({\texttimes}2 ambient) levels of CO2, aboveground biomass production and leaf water potentials were increased significantly compared with those of plants in OTCs with ambient CO2. There were no differences in leaf area or leaf number per tiller in A. gerardii in elevated compared with ambient OTCs. However, leaf area in adjacent unchambered plots with greater water availability was significantly higher than in the OTCs. The time required for developing leaves to achieve maximum leaf area was reduced by 29\%, and the period of time until leaves senesced was increased by 20\% for plants exposed to elevated compared with ambient CO2. Thus, leaves of this C4 grass species expanded more rapidly (6 d) and remained green longer (9 d) when exposed to elevated CO2. Such CO2-mediated increases in leaf longevity in the dominant species may allow this grassland to respond more opportunistically to temporally variable rainfall patterns in high-CO2 environments. These responses should be included in leaf-based simulation models that attempt to mechanistically link physiological alterations to predicted canopy responses to increased CO2.},
	keywords = {LTER-KNZ, Ecophysiology, elevated carbon dioxide, grassland, leaf lifespan, tallgrass prairie, Water relations},
	doi = {10.1086/314202},
	author = {Alan K. Knapp and Bargman, N. and Maragni, L.A. and McAllister, C.A. and D. Bremer and J.M. Ham and Owensby, C.E.}
}
@article {KNZ00656,
	title = {Is leaf-level photosynthesis related to plant success in a highly productive grassland?},
	journal = {Oecologia},
	volume = {117},
	year = {1998},
	pages = {40 -46},
	abstract = {We addressed the question: {\textquotedblleft}Are short-term, leaf-level measurements of photosynthesis correlated with long-term patterns of plant success?{\textquotedblright} in a productive grassland where interspecific competitive interactions are important. To answer this question, seasonal patterns of leaf-level photosynthesis were measured in 27 tallgrass prairie species growing in sites that differed in species composition and productivity due to differences in fire history. Our specific goals were to assess the relationship between gas exchange under field conditions and success (defined as aerial plant cover) for a wide range of species, as well as for these species grouped as dominant and sub-dominant grasses, forbs, and woody plants. Because fire increases productivity and dominance by grasses in this system, we hypothesized that any relationship between photosynthesis and success would be strongest in annually burned sites. We also predicted that regardless of fire history, the dominant species (primarily C4 grasses) would have higher photosynthetic rates than the less successful species (primarily C3 grasses, forbs and woody plants). Because forbs and woody species are less abundant in annually burned sites, we expected that these species would have lower photosynthetic rates in annually burned than in infrequently burned sites. As expected, the dominant C4{\textvisiblespace}grasses had the highest cover on all sites, relative to{\textvisiblespace}other growth forms, and they had the highest maximum and seasonally averaged photosynthetic rates (17.6 {\textpm} 0.42 μmol m-2 s-1). Woody species had the lowest average cover as well as the lowest average photosynthetic rates, with subdominant grasses and forbs intermediate in both cover and photosynthesis. Also as predicted, the highest overall photosynthetic rates were found on the most productive annually burned site. Perhaps most importantly, a positive relationship was found between leaf-level photosynthesis and cover for a core group of species when data were combined across all sites. These data support the hypothesis that higher instantaneous rates of leaf-level photosynthesis are indicative of long-term plant success in this grassland. However, in contrast to our predictions, the subdominant grasses, forbs and woody species on the annually burned site had higher photosynthetic rates than in the less frequently burned sites, even though their average cover was lower on annually burned sites, and hence they were less successful. The direct negative effect of fire on plant cover and species-specific differences in the availability of resources may explain why photosynthesis was high but cover was low in some growth forms in annually burned sites.},
	keywords = {LTER-KNZ, Competition, grassland, photosynthesis, Plant cover, tallgrass prairie},
	doi = {10.1007/s004420050629},
	author = {McAllister, C.A. and Alan K. Knapp and Maragni, L.A.}
}
@article {KNZ00590,
	title = {Photosynthetic gas exchange and water relations responses of three tallgrass prairie species to elevated carbon dioxide and moderate drought},
	journal = {International Journal of Plant Science},
	volume = {158},
	year = {1997},
	pages = {608 -616},
	abstract = {Undisturbed tallgrass prairie was exposed to ambient and elevated (twice-ambient) levels of atmospheric CO2 and experimental dry periods. Seasonal and diurnal midday leaf water potential (Ψ leaf), net photosynthesis $(A_{\text{net}})$, and stomatal conductance (g s) responses of three tallgrass prairie growth forms{\textemdash}a C4 grass, Andropogon gerardii; a broad-leaved woody C3 shrub, Symphiocarpos orbiculatus; and a C3 perennial forb, Salvia pitcheri{\textemdash}were assessed. $\Psi _{\text{leaf}}$ in A. gerardii and S. orbiculatus was higher under elevated CO2, regardless of soil moisture, while $\Psi _{\text{leaf}}$ in S. pitcheri responded only to drought. Elevated CO2 always stimulated $A_{\text{net}}$ in the C3 species, while A. gerardii $A_{\text{net}}$ increased only under dry conditions. However, $A_{\text{net}}$ under elevated CO2 in the C3 species declined with drought but not in the C4 grass. Under wet conditions, g s reduced in elevated CO2 for all species. During dry periods, gs at elevated CO2 was sometimes higher than in ambient CO2. Our results support claims that elevated CO2 will stimulate tallgrass prairie productivity during dry periods and possibly reduce temporal and spatial variability in productivity in these grasslands.},
	keywords = {LTER-KNZ, Water relations},
	url = {http://www.jstor.org/stable/2474921},
	author = {Hamerlynck, E.P. and McAllister, C.A. and Alan K. Knapp and J.M. Ham and Owensby, C.E.}
}
@mastersthesis {KNZ00601,
	title = {The relationship between leaf-level photosynthetic rates and success in a high productivity grassland},
	volume = {MS Thesis},
	year = {1997},
	pages = {1 -49},
	school = {Kansas State University},
	type = {M.S. Thesis},
	address = {Manhattan, KS},
	keywords = {LTER-KNZ},
	author = {McAllister, C.A.}
}
