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Title: Elevated CO2 and warming differentially impact carbon isotope discrimination and tissue N concentration in five grassland species

Author
item SAGE, EMMA - University Of Wyoming
item PENDALL, ELISE - University Of Wyoming
item WILLIAMS, DAVID - University Of Wyoming
item Lecain, Daniel
item Morgan, Jack

Submitted to: Ecological Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2009
Publication Date: 8/1/2009
Citation: Sage, E., Pendall, E., Williams, D., Lecain, D.R., Morgan, J.A. 2009. Elevated CO2 and warming differentially impact carbon isotope Discrimination and tissue N concentration in five grassland species. Ecological Society of America Proceedings. COS 42-10.

Interpretive Summary:

Technical Abstract: We measured carbon isotope discrimination ('13C) and tissue N concentration in above ground biomass over four years at the Prairie Heating and CO2 Enrichment (PHACE) experiment in southeastern Wyoming, USA. This factorial experiment combined FACE (ambient and elevated [600 ppm] CO2 concentration), experimental warming (1.5°C daytime, 3°C nighttime) and irrigation to evaluate direct, indirect and interactive effects of global changes on semi-arid grassland structure and function. We sampled species representing four functional types: a C4 grass Bouteloua gracilis; a C3 perennial sedge Carex eleocharis; a C3 taprooted forb Sphaeralcea coccinea; and two C3 grasses Pascopyrum smithii and Hesperostipa comata. '13C was reduced similarly by about 2‰ for all species under elevated compared to ambient [CO2], suggesting that at least for C3 species stomatal closure under elevated [CO2] reduced CO2 supply relative to carboxylation capacity. Experimental warming by itself did not alter '13C for any species. However, experimental warming lessened effects of elevated [CO2] on this integrated gas exchange trait. Tissue N concentration was reduced by an average of 0.2 ± 0.05% in elevated compared to ambient [CO2] across all species, and experimental warming lessened this difference. Irrigation had little effect on either of these plant traits. The apparent interaction between elevated [CO2] and warming on '13C and tissue N concentration was unexpected and is potentially attributed to 1) accelerated phenological development with warming; 2) warming-induced changes in leaf structure and anatomy; or 3) indirect and interactive effects of warming on soil nitrogen availability.