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Relative effects of experimental warming on photosynthesis and respiration of C3 and C4 species in a tall grass prairie .
Liu, Xiaozhong*,1, Luo, Yiqi1, Wallace, Linda1, 1 University of Oklahoma, Norman, Oklahoma
ABSTRACT- Global mean air temperature will increase by 1.0 to 5.8oC before 2100. It is unclear what impacts the global warming will have on tall grass species. We examined leaf net photosynthetic rate (Pn) and dark respiration rate (Rd) of Aster ericoides (C3) and Sorghastrum nutans (C 4) in response to experimental warming in an Oklahoma tall grass prairie in 2001. Artificial warming treatments have been implemented with twin tube quartz radiators since 21 November 1999. Pn significantly increased in April and decreased from June to September for Aster ericoides, increased from April to June and decreased in September and October for Sorghastrum nutans, and did not change in other months for either species under warming in comparison to that under control. Rd of both species significantly increased from April to July and did not change after August under warming. Measured leaf temperature response curves of Pn showed unchanged in summer and down-regulation in fall for Aster ericoides, and up-regulation in summer and down-regulation in fall for Sorghastrum nutans under warming. That curves of Rd showed up-regulation in summer and unchanged in fall for Aster ericoides, and unchanged in summer and down-regulation in fall for Sorghastrum nutans. Warming also shift Pn optimum temperature 1-30C higher in Sorghastrum nutans. Results indicated warming treatment stimulated photosynthesis in early growing season, and decreased photosynthesis and lead to early senescence in later growing season for both for both C3 and C4 grasses. Photosynthesis of C4 grass acclimated to warming better than that of C3 grass.
KEY WORDS: experimental warming , photosynthesis, respiration, tall grass prairie