@article {KNZ00574,
	title = {Responses of a C4 grass and three C3 forbs to variation in nitrogen and light in tallgrass prairie},
	journal = {Ecology},
	volume = {77},
	year = {1996},
	pages = {1738 -1749},
	abstract = {In tallgrass prairie, high plant species diversity results not from a large number of grass species, but from a large number of forb (nongrass, herbaceous) species. Forbs exhibit morphological, life history, and ecophysiological characteristics that contrast sharply with those of the dominant C4 grasses. Success of the subdominant forbs varies strongly with topographic position and burning regime, and landscape scale patterns of abundance are well documented. But comparatively little is known about the mechanisms determining these patterns in persistent tallgrass prairie forbs. To elucidate these mechanisms, (1) leaf{\textemdash}level physiological characteristics of the dominant C4 grass, Andropogon gerardii, and four co{\textemdash}occurring C3 forbs were measured in response to natural and experimentally manipulated gradients of N availability, and (2) seasonal light environments of forbs in contrasting topographic positions and burning regimes and their morphological and physiological responses in these environments were compared to determine whether resource availability and utilization patterns contributed to patterns of forb distribution and abundance. The effects of burning regime and topographic position on maximum rate of photosynthesis (A) and stomatal conductance to water vapor (g) measured at the leaf level were not consistent with patterns of forb abundance. Nitrogen did not appear to limit forb physiological processes, even though increased N availability resulted in higher tissue N concentrations and greater biomass. There was no consistent increase in (A) or decrease in (g) in response to fertilization. However, (A) at low light levels was as much as 67\% higher in fertilized Vernonia baldwinii and A. gerardii compared to unfertilized plants. Greater light availability to forbs in the canopy was associated with lower grass biomass production in uplands compared to lowlands and in unburned compared to burned sites. Forbs did not appear to adjust morphologically (leaf area and plant height) to different light environments at different sites. As a result, as much as 90\% of forb leaf area in the burned lowland was displayed in low light, whereas as little as 30\% of forb leaf area was in low light in the uplands at midseason. Estimates of potential whole{\textemdash}plant carbon uptake, based on leaf area distribution relative to available light and (A) as a function of light availability, agreed well with patterns of forb abundance and production. Differences in light availability may account for much of the variability in forb abundance related to burning regime and topographic position by limiting carbon gain in forbs more in burned lowlands than in other sites.},
	keywords = {LTER-KNZ, tallgrass prairie},
	doi = {10.2307/2265779},
	author = {Turner, C.T. and Alan K. Knapp}
}
@article {KNZ00523,
	title = {Comparative gas exchange and nitrogen responses of the dominant C4 grass, Andropogon gerardii, and five C3 forbs to fire and topographic position in tallgrass prairie during a wet year},
	journal = {International Journal of Plant Science},
	volume = {156},
	year = {1995},
	pages = {216 -226},
	abstract = {High plant species diversity in tallgrass prairie results not from a large number of grass species but, rather, from a large number of forb (nongrass, herbaceous) species. Although morphological characteristics of tallgrass prairie forbs differ strongly from those of the grasses and their patterns of abundance vary substantially with burning regime and topographic position, comparatively little is known about the ecology of persistent tallgrass prairie forbs. We measured leaf-level physiological characteristics of the dominant C4 grass, Andropogon gerardii, and five co-occurring C3 forb species in response to burning regime and topographic position to determine if there were either absolute or seasonal differences in resource utilization patterns that could contribute to the patterns of forb distribution and abundance in tallgrass prairie. In a wet year, neither fire nor topographic position affected leaf-level physiological characteristics in the grass and forbs studied, and thus responses were not consistent with extant patterns of forb abundance (greater forb abundance in unburned and upland sites). Water use efficiency in A. gerardii was 40\%-170\% greater and foliar N concentration was consistently lower in the grass than in the forbs, but there were no distinct or consistent differences between the grass and forbs in maximum rates of photosynthesis and stomatal conductance or xylem pressure potential. Moreover, seasonal patterns of gas exchange in forbs and the grass were not different, as might be expected when comparing C3 and C4 species. These results indicate that, when assessed at the leaf level, responses of these prairie plants to fire or topographic position during a wet year are not indicative of their success in these sites. However, seasonal water stress is a typical feature of the tallgrass prairie environment and water use patterns indicate that the prevalence of soil moisture limitations in most years may be a key factor influencing plant distribution and success in this ecosystem.},
	keywords = {LTER-KNZ, tallgrass prairie},
	url = {http://www.jstor.org/stable/2474960},
	author = {Turner, C.T. and Kneisler, J.R. and Alan K. Knapp}
}
