Response Mechanism of Photosynthesis and Nitrogen Partitioning in Phoebe bournei Seedlings Under Different CO₂ Concentrations

In order to further investigate the effects of elevated CO₂ concentration on photosynthesis, especially on nitrogen nutrition and nitrogen distribution in leaves of Phoebe bournei seedlings were studied. The open-top air chamber was used to cultivate P. bournei seedlings with different CO₂ concentrations. The results show that there was no significant effect of 500 μmol/mol treatment on the photosynthetic characteristic parameters, leaf nitrogen content, leaf nitrogen distribution and photosynthetic nitrogen use efficiency(PNUE) of P. bournei seedlings. The Vcmax, nitrogen content, nitrogen distribution in the carboxylated part of leaf(N_C) and PNUE in the carboxylated part of P. bournei seedlings treated with 700 μmol/mol decreased significantly, Vcmax, N_C and PNUE were decreased by 21.65%, 12.73% and 14.78%, respectively. The photosynthesis and nitrogen utilization of P. bournei seedlings were not affected by the appropriate increase of CO₂ concentration, the significant increase of CO₂ concentration resulted in the decrease of nitrogen content and utilization efficiency, which may be the reason for the decrease of photosynthesis in P. bournei seedlings under high CO₂ concentration.