Leaf gas exchange of <i>Andropogon gerardii</i> Vitman, <i>Panicum virgatum</i> L., and <i>Sorghastrum nutans</i> (L.) Nash in a tallgrass prairie

Abstract

Net CO 2 assimilation as a function of internal CO 2 and stomatal conductance to water vapor were measured on blades of the C 4 grasses Andropogon gerardii Vitman, Panicum virgatum L., and Sorghastrum nutans (L.) Nash in northeast Kansas over two growing seasons to determine the comparative physiological responses of these dominant grasses of the tallgrass prairie to environmental variables. The response of dark respiration to temperature and of net assimilation to CO 2 concentration and absorbed quantum flux differed little among species. A. gerardii had lower potential photosynthetic rates at internal CO 2 concentrations below saturation than P. virgatum and S. nutans , but net assimilation under ambient conditions was similar in the three species. Net assimilation and both the initial slope of assimilation versus internal CO 2 curves and the maximum potential assimilation rate decreased as leaf water potential declined in blades of A. gerardii and S. nutans . Changes in assimilation capacity were paralleled by changes in stomatal conductance that were similar in all three species. The strong correlations among processes regulating leaf CO 2 assimilation and transpiration in A. gerardii , P. virgatum , and S. nutans suggest that the processes are tightly and similarly coupled in these grasses over a wide range of environmental conditions encountered in the tallgrass prairie.