Responses of photosynthesis, growth and water use efficiency of Avena sativa to drought under different CO2 concentrations

The interaction of CO2 concentration and soil moisture on photosynthesis, growth and water use efficiency in oat (Avena sativa) was observed in the walkin CO2 chamber. The results showed that low CO2 concentration inhibited photosynthesis and biomass production of oat greatly while elevated CO2 promoted them slightly. With soil moisture content declined, net photosynthetic rate and water use efficiency didnt change, whereas biomass and leaf N contents slightly decreased, and the ratio of root to shoot increased at low CO2 concentration. Net photosynthetic rate, the ratio of root to shoot and water use efficiency increased, whereas biomass significantly decreased, and leaf N content did not change at high CO2 concentration. These results suggested that low CO2 concentration did not intensify the negative effects of drought, and high CO2 concentration failed to relieve the negative effects of drought stress on oat. The adaptation of oat to low CO2 concentration may limit its responses to future high CO2 concentration.