Abstract: The effects of elevated CO2 concentration and increased temperature on photosynthetic characteristics and nitrogen metabolism of soybean leaves were studied in order to provide reference for soybean production under climate change in the future. In this experiment, soybean variety‘Zhonghuang35’ was used as the test material. The experiment was carried out at four treatments: CK (the CO2 concentration and air temperature were consistent with atmosphere measurement value), EC(the CO2 concentration is the measured value in the atmosphere + 200μmol·mol–1; the air temperature was consistent with atmosphere measurement value), ET (the CO2 concentration was consistent with atmosphere measurement value; the air temperature was the measured value in the atmosphere +2℃), and ECT (the CO2 concentration was the measured value in the atmosphere +200μmol·mol–1 and the air temperature was the measured value in the atmosphere + 2℃).The soybean was planted in the artificial climate chamber throughout the growth period. At the seed filling stage of soybean, we measured the relative chlorophyll content of soybean leaves by leaf chlorophyll meter, photosynthetic parameters by portable gas exchange system, light response curves and CO2 response curves by portable photosynthesis measurement system, and measured the leaf nitrogen metabolism related indeices, through these experiment results to study the effect of CO2 concentration elevated by 200μmol·mol–1 and air temperature increased by 2℃ on photosynthetic characteristics and key indicators of nitrogen metabolism of soybean leaves at seed filling stage. The results showed that: (1) ET treatment significantly increased the relative chlorophyll content (SPAD) of soybean leaves at seed filling stage, but EC treatment and ECT treatment had no significant effect on SPAD. (2) The stomatal conductance (Gs) of soybean leaves at seed filling stage was decreased significantly in all treatments. Net photosynthetic rate (Pn) and water use efficiency (WUE) of leaves was decreased significantly in ET treatment. EC treatment had little effect on Gs of soybean leaves, but it could improve WUE of soybean leaves and alleviate the negative effect of ET treatment. (3) EC treatment and ET treatment significantly decreased the maximum net photosynthetic rate (Pnmax) of soybean leaves at seed filling stage, but ECT treatment had no significant effect on it. (4) In EC treatment, CO2 compensation point (Γ), saturated intercellular CO2 concentration (Cisat) and photorespiration rate (RP) of soybean leaves were significantly increased, but ET treatment and ECT treatment had little effect on them all treatments decreased the maximum net photosynthetic capacity (Amax) of soybean leaves at seed filling stage. (5) The nitrate reductase (NR) activity and soluble protein content of soybean leaves was decreased significantly in EC treatment, while the soluble protein content of soybean leaves was increased significantly in ET treatment and ECT treatment, but NR activity and glutamine synthetic (GS) activity was not significantly changed. In conclusion, in this experiment, elevated CO2 concentration by 200μmol·mol–1alleviated the negative effect of increased air temperature by 2℃ on photosynthesis of soybean leaves at seed filling stage, but the nitrogen metabolism was inhibited. Increased air temperature by 2℃ can alleviate the inhibition of CO2 concentration by 200μmol·mol–1 on nitrogen metabolism to a certain extent.

Key words: Elevated CO2 concentration, Increased air temperature, Soybean, Photosynthetic characteristics, Nitrogen metabolism