Effects of atmospheric CO_2 enrichment and nitrogen application rate on photosynthetic parameters and water use efficiency of spring wheat

The top-open chamber was used to simulate elevating atmospheric CO2 concerntration,where wheat(Triticum aestivum L.) was grown under different N application levels and atmospheric CO2 concerntration to study the response of wheat photosynthesis and water use efficiency(WUE) to the change of these two factors and the regulation mechnism of nitrogen application.The results showed that the net photosynthetic rate(Pn),intercellular CO2 concentration(Ci),stomatal limitation value(Ls) and WUE were increased,but stomatal conductance(Gs) decreased gradually,while,transpiration rate(Tr) decreased first and then increased with nitrogen levels increasing under high atmospheric CO2 concentration conditions.Compared to ambiment atmosphric CO2 treatments,Pn was decreased significantly in 0 and 0.1 g N/kg(soil) treatments and significantly increased in 0.2 g N/kg treatment with different atmospheric CO2 concerntration,while Gs,Ci and Tr were decreased.Ls and WUE got to the highest in 0.2 g N/kg,and the differences were significant compared to the other treatments.Pn and Ls were significantly increased with nitrogen levels under the condition of different atmospheric CO2 concerntration.but the response of Ci and Tr were inconsistent.So,WUE and Ls was significantly increased under long-term high CO2 concentration.The photosynthetic down-regulation occured in 0 and 0.1 g N/kg,but not under 0.2g N/kg treatment.