Abstract: The light response curves of Castanopsis sclerophylla leaves, a constructive species in subtropical forest, were measured under four different CO₂ concentrations, and were fitted with five models to explore the optimal models for different CO₂ concentrations and investigate the adaptability of parameters of C. sclerophylla to CO₂ concentrations. The results showed that the fitting effects of the five models were in descending order of modified rectangular hyperbola model > modified exponential model > exponential model > non-rectangular hyperbola model > rectangular hyperbola model. The light saturation point (LSP) and the maximum net photosynthetic rate (P_max) were best fitted by modified rectangular hyperbola model, and the dark respiration rate (R_d) was best fitted by non-rectangular hyperbola model. The adaptability of the five models to different CO₂ concentration varied. Rectangular hyperbola model, exponential model, and modified rectangular hyperbola model were fitted well to the curves under low CO₂ concentration, non-rectangular hyperbola model to high CO₂ concentration. The light compensation point (LCP) and R_d of C. sclerophylla decreased with the increased CO₂ concentration and P_max increased with the increased CO₂ concentration. In conclusion, increased CO₂ concentration can improve the photosynthesis and facilitate its use to low light for C. sclerophylla leaves, and suppressed its respiration.

Key words: N application rate, leaching, accumulation, winter wheat and summer maize rotation system, nitrate nitrogen, long-term experiment