Effects of drought on the light response and the dynamic correlation among photosynthetic physiological indicators of Phyllostachys edulis at different ages

Against the backdrop of intensifying global climate change, drought stress has become a key limiting factor affecting the stability and productivity of bamboo forest ecosystems. The "ceiling method" was used to simulate throughfall exclusion for the bamboo forest. The Li-6400 portable photosynthesis meter was used to measure the seasonal changes in light response of different ages of bamboo under different drought treatments in situ. The dynamic response of bamboo photosynthetic capacity to drought at different ages was analyzed through the correlation between photosynthetic physiological indicators, aiming to provide theoretical basis for sustainable management of bamboo under climate change. The results showed that when the photosynthetically active radiation (PAR) was less than 200μmol/（m² • s）, the net photosynthetic rate (P_n) for leaves of different ages of bamboo increases rapidly with the increase of PAR under different drought treatments. When PAR> 200μmol/（m² • s）, the P_n gradually increases to the highest and remains stable. There were significant differences (P<0.05) in the photosynthetic parameters of bamboo at different ages among seasons, ages, and drought treatments. Under drought conditions, the P_{n max} and AQY of 5 years old bamboo (D_5a) were higher than those of the control bamboo (CK_5a) in all seasons except autumn. The light compensation point (LCP) in summer and light saturation point (LSP) in winter were significantly lower than those of the control bamboo (P<0.05). Under drought conditions, the LSP of 3 years old bamboo (D_3a) in summer and autumn was higher than that of the control (CK_3a), while the P_{n max}, R_d in autumn and winter, and LCP in winter were all lower than those of the control. Under drought conditions, the P_{n max} of one year old bamboo (D_1a) in summer and autumn was significantly higher than that of the control bamboo (CK_1a), while the AQY in spring and winter and LCP and R_d in autumn were lower than those of the control. Drought treatment significantly reshaped the stomatal regulation and water use strategy of bamboo, showing significant seasonal and age differences (P<0.05). Under drought conditions, the synergy between stomatal conductance (G_s) and transpiration rate (T_r) in bamboo remains stable. 5 years old bamboo improved the positive correlation between instantaneous water use efficiency (WUE) and leaf saturated vapor pressure difference (VpdL) through stomatal optimization regulation to alleviate drought stress, while one year old bamboo was significantly weaker in drought resistance due to non-stomatal limitations.