Combination of elevated CO2 concentration and elevated temperature and elevated temperature only promote photosynthesis of Quercus mongolica seedlings

One-year-old oak (Quercus mongolica Fisch.) seedlings were grown in growth chambers for 30 days to investigate the effects of the combination of elevated CO2 concentration ([CO2], 700 mu mol/mol) and temperature (ambient T + 4 degrees C) and only elevated temperature (ambient T +4 degrees C) on leaf gas exchange, chlorophyll a fluorescence, and chlorophyll content. In the growth chambers, natural conditions of the Maoershan mountain regions of Heilongjiang Province (45-46 degrees N, 127-128 degrees E) of China for the average growth season were simulated. The results showed that the maximum net photosynthetic rate (P-Nmax) was approximate to 1.64 times greater at elevated temperature than at ambient temperature. The irradiance saturation point (I-s), apparent quantum yield (AQY), maximum photosystem II efficiency (F-v/F-m), and chlorophyll content significantly increased, while irradiance compensation point (I (c)) was not affected by elevated temperature. The combination of elevated [CO2] and temperature also significantly increased P-Nmax by approximately 34% but much lower than that under elevated temperature only. In the case of factor combination, dark respiration (R-d), I-c, F-v/F-m, and total chlorophyll content increased significantly, while I-s and AQY were not affected. Moreover, under elevated [CO2] and temperature, R-d and I-c, F-v/F-m were significantly higher than under elevated temperature only. The results indicated that the combination of elevated [CO2] and temperature expected in connection with the further global climate change may affect carbon storage of the coenotype of Q. mongolica in this region of China.