Interactive effects of changing precipitation and elevated CO2 concentration on photosynthetic parameters of Stipa breviflora
降水与CO2浓度协同作用对短花针茅光合特性的影响

Aims Stipa breviflora, which is a dominant species of desert steppe in the arid region of China, would be seriously affected by changes of precipitation and atmospheric CO2 concentration. Our objective is to determine the interactive effects of changing precipitation and elevated CO2 concentration on photosynthetic parameters of S. breviflora, in order to evaluate the effects of future climate change on the desert steppe. Methods Open top chambers （OTCs） were used to simulate the elevated CO2 concentration （control, 450, and 550 μmol·mol –1 ） and changing precipitation （–30%, –15%, 0, +15% and +30%, based on the average monthly precipitation during 1978–2007）. The photosynthetic parameters of S. breviflora were measured by a LI-6400 portable photosynthesis system. Important findings The responses of photosynthetic parameters of S. breviflora to changes of CO2 concentration and precipitation were significant, and interactive effects were observed. With increased CO2 , leaf net photosynthetic rate （Pn ） of S. breviflora increased, and photosynthetic acclimation occurred during August. Stomatal conductance （Gs ） and transpiration rate （Tr ） decreased, and the increase of Pn was more than Tr . As a result, its water use efficiency （WUE） increased. With increased precipitation, Pn , Gs and Tr increased, and the increase of Pn was less than Tr , resulting in a decrease in WUE. Under higher CO2 and 15% increase in precipitation, Pn , Gs and Tr of S. breviflora increased greatly, the increase of P n was close to Tr , and consequently WUE did not change significantly.