Objective In the context of global climate change, this study aimed to reveal differences in the photosynthesis-light response dynamics of Phyllostachys edulis under drought conditions with different rainfall exclusion intensities and drought durations, and to clarify its adaptative strategies to drought stress.

Method Drought treatments were simulated using the throughfall exclusion method, with a non-drought treatment as the control. Photosynthetic light-response curves of P. edulis under different drought durations were measured in situ using a Li-6400 portable photosynthesis system. The dynamic responses of photosynthetic parameters to drought, as well as the drought adaptation strategies of moso bamboo, were fitted and analyzed.

Result The results showed that the net photosynthetic rate (P_n) of different ages of bamboo leaves under different drought treatments initally increased with increasing photosynthetically active radiation (PAR) under reaching a critical point, after which it gradually leveled off. Photoinhibition occurred in grade II bamboo after 3 years of drought in spring, and in grade III bamboo after 5 years of drought in summer and winter. Drought treatment significantly inhibited the maximum net photosynthetic rate (P_nmax) of bamboo (p<0.05), with significant decreases of P_nmax in most seasons after 1 and 3 years of drought (grade I and II bamboo). However, in winter, after 5 years of drought, P_nmax showed adaptive improvement in winter. With increasing drought duration, P_nmax increased significantly in spring, summer, and winter (p<0.05), while in autumn it increased first and then decreased significantly(p<0.05). Seasonal variation in P_nmax was most pronounced in summer. Under drought conditions, the apparent quantum efficiency (AQY) of bamboo was significantly impaired (p<0.01), although AQY increased abnormally in summer after 1 year of drought. Under drought conditions, the dark respiration rate (R_d) of bamboo showed an age-specific response. After 1 year and 3 years of drought, R_d generally increased, while after 5 years of drought it decreased significantly in autumn. Drought also significantly reduced the light saturation point (LSP) (p<0.01), indicating a weakened capacity to adapt to strong light. P_nmax of grade III bamboo was highest in spring and summer, whereas that of grade II bamboo peaked in autumn; P_nmax was lower for all bamboo ages in winter. These results indicate that photosynthetic capacity was significantly affected by both drought duration and rainfall exclusion. Among the drought treatments, P_nmax in winter after 5 years of drought and LSP, AQY, and Rd in winter after 3 years of drought were more likely to exhibit adaptive improvement.

Conclusions Under drought conditions, the drought resistant physiological system of bamboo was fragile, whereas older bamboo subjected to 5 years of drought exhibited stronger drought resistance. The P_n after 1 year of drought was significantly positively correlated with stomatal conductance (Cond) and leaf temperature (T_leaf) (p<0.05), while the P_n after 5 years of drought was significantly positively correlated with T_leaf (p<0.05). The P_n after 3 years of drought was significantly positively correlated with Cond (p<0.05), and significantly negatively correlated with leaf saturated vapor pressure difference (VpdL) and air temperature (T_air) (p<0.05); Under all drought durations, P_n was significantly negatively correlated with atmospheric CO₂ concentration (C_a) (p<0.05). As drought duration increased, the positive factors affecting P_n gradually decreased, while the negative factors gradually increased.