Abstract: Precipitation will be changed by elevated atmospheric CO₂ concentration in the future,which will seriously affect on the desert ecosystem.Our objective was to determine the interactive effects of elevated CO₂ concentration and changing precipitation on photosynthetic physiology of Reaumuria soongorica which is dominant species of desert,in order to evaluate the response of desert ecosystem to future climate change.Open top chambers were used to simulate the elevated CO₂ concentration (350,550,and 700 μmol·mol^-1) and changing precipitation (30%,15%,0,+15%,+30%).The photosynthetic physiology indexes such as net photosynthetic rate,transpiration rate,stomatal conductance and water use efficiency of R.soongorica seedlings were measured in June,July and August.The results showed that,with increased CO₂ concentration,net photosynthetic rate of R.soongorica increased obviously whether precipitation increased or decreased,which meant that the photosynthetic capacity of R.soongorica had a wide adaptability to precipitation under short elevated CO₂.But photosynthetic capacity of R.soongorica decreased under long elevated CO₂ and photosynthetic acclimation occurred during August.Transpiration rate and stomatal conductance decreased with increased CO₂ concentration,but the results were opposite with increased precipitation because of the compensation.Wateruse efficiency increased significantly with increased CO₂ concentration,especially under decreased precipitation treatment,but this reaction was smaller under long elevated CO₂ than under short elevated CO₂.The results suggest that at ambient CO₂ levels,photosynthetic ability of R.soongorica increases with precipitation increasing,and drought resistance increases with water use efficiency increasing under decreased precipitation,which enhance the ability of R.soongorica to climate warming and rying in the future.

Key words: CO₂, precipitation, photosynthetic physiology, water use efficiency, Reaumuria soongorica