Responses of photosynthetic characteristics,stomatal conductance and transpiration of wheat to the increase of atmospheric CO_(2) concentration

The net photosynthesis (Pn),stomatal conductance(Cs),transpiration(Tr),water use efficiency(WUE) and chlorophyll content of wheat leaves under ambient and elevated CO_2 levels were measured, and their responses to the increase of CO_2 were discussed. The results showed that daily average Pn increased by 20.8% and 29.7% at earing stage under 550 and 750 μmol·mol~(-1),compared to the ambient air CO_2 concentration. At the same time, midday depression of photosynthesis disappeared. The average Cs decreased by 15.3% and 21.7% at different growth stages with air CO_2 enrichment. The average Tr reduced by 4.5% and 9.4%.WUE increased significantly by 19.2%~25.7% and 32.2%~45.6% in two elevated CO_2 levels. It was also found that chlorophyll a ,chlorophyll b, chlorophyll and carotenoid contents of wheat leaves increased by 11.0%~14.8%,13.0%~18.2%, 11.5%~15.7% and 15.3%~23.5% at earing stage. However, the ratio of chlorophyll a to chlorophyll b reduced under two elevated CO_2 conditions.