|Nippert, J - UNIVERSITY OF KANSAS|
|Knapp, A - COLORADO STATE UNIVERSITY|
Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 28, 2006
Publication Date: June 1, 2007
Citation: Nippert, J.B., Fay, P.A., Knapp, A.K. 2007. Photosynthetic traits in C3 and C4 grassland species in mesocosm and field environments. Environmental and Experimental Botany. 60:412-420. Interpretive Summary: This paper presents data collected to test a basic hypothesis in grassland ecology; that grasses with C4 photosynthesis dominate in the tallgrass prairie because of their greater physiological resource efficiency compared to co-occurring plants species with C3 photosynthesis. The hypothesis was tested by conducting measurements of leaf level physiological processes related to carbon gain and water loss on seven C3 and C4 species, in quasi-natural microcosms with high resource availability compared to intact native grasslands which have been shown in past studies to experience multiple resource limitations. C3 and C4 species failed to show expected differences in resource use efficiency in field compared to microcosm conditions. The results suggest instead that C4 species shift their resource use strategies as conditions change through the growing season.
Technical Abstract: The North American tallgrass prairie is composed of a diverse mix of C3 and C4 plant species that are subject to multiple resource limitations. C4 grasses dominate this ecosystem, purportedly due to greater photosynthetic capacity and resource use-efficiency associated with C4 photosynthesis. We tested the hypothesis that intrinsic physiological differences between C3 and C4 species are consistent with C4 grass dominance by comparing leaf gas exchange and chlorophyll fluorescence variables for 7 C4 and C3 herbaceous species in two different settings: experimental microcosms with abundant resources and natural grassland sites with more limited resources. In the microcosms, C4 grasses had higher photosynthetic rates (Amax at ambient Ca), water potentials and water use efficiency than the C3 species. These differences were absent in the field, where several variables suggested that N limitation reduced photosynthetic rates in all non-leguminous species. Thus, intrinsic photosynthetic advantages for C4 species measured in resource-rich microcosms could not explain the dominance of C4 species in the field. Instead, C4 dominance in this ecosystem may depend more on the ability of the grasses to grow rapidly when resources are plentiful and to tolerate multiple limitations when resources are scarce.