Abstract: To investigate the physiological and ecological strategies of light adaptation in subtropical broadleaved tree species, the modified rectangular hyperbola model and the FvCB model were used to fit the fluorescence CO₂ response curves (A/C_i curves) of Sapium sebiferum, Cyclobalanopsis glauca, and Castanopsis sclerophylla under different light intensities (200, 500, 800, and 1100 μmol·m^-2·s^-1). The photosynthetic physiological and biochemical characteristics of these species were then analyzed. The results showed that when intercellular CO₂ concentration (C_i)<30 Pa, leaf net photosynthetic rate (A) of the three tree species increased almost linearly, and the greater the light intensities, the greater the increase of A. When C_i>30 Pa, the increase of A tended to be slow. Under the same C_i, A increased significantly with the increase of light intensity. Stomatal conductance (g_s) decreased with the increase of C_i. Under the same C_i, g_s increased significantly with the increases of light intensity. When C_i<35 Pa, the electron transport rate (J) of PSII increased significantly with the increases of C_i. When C_i>35 Pa, J tended to be stable with the increases of C_i. Under the three light intensities (500, 800 and 1100 μmol·m^-2·s^-1), initial carboxylation efficiency (Φ_c) was significantly greater than that at light intensity of 200 μmol·m^-2·s^-1. When light intensity >500 μmol·m^-2·s^-1, leaf photosynthetic capacity (P_nmax) of the three species were higher than that at lower light intensities. Mesophyll conductance (g_m) increased significantly with the increases of light intensity. The maximum electron transfer rate (J_max), maximum carboxylation rate of Rubisco (V_cmax), and light dark respiration rate (R_d) were not affected by light intensity. Sapium sebiferum, Cyclobalanopsis glauca, and Castanopsis sclerophylla could enhance photosynthetic carbon sequestration capacity by increasing g_m and light energy utilization efficiency under high light intensities, and the photosynthetic physiological and biochemical characteristics responded significantly to light intensity changes, which provide an important theoretical basis for the breeding of subtropical plantation tree species and the prediction of forest carbon sink dynamics under the background of global climate change.

Key words: photosynthesis, FvCB model, photosynthetically active radiation, light response, photosynthetic parameter