Objective To explore the response of leaf anatomy and leaf photosynthetic physiology to long-term drought and analyze the relationship between leaf anatomy and leaf photosynthetic physiology under long-term drought conditions.

Method We conducted a manipulation drought experiment by reducing the throughfall in the forest and measured the leaf gas exchange, chlorophyll fluorescence, leaf nutrient (N, P) and leaf anatomy of the two typical tree species (Pinus massoniana Lamb. and Castanopsis hystrix Miq.) in subtropical China at the 8th year after the throughfall reduction treatment.

Results(1) Significant differences were observed in leaf anatomy between P. massoniana and C. hystrix in response to throughfall reduction; the upper and lower epidermis, leaf thickness and stomatal density of P. massoniana needles increased significantly. However, the thickness of the upper epidermis of the leaves of C. hystrix increased significantly, and the thickness of the spongy tissue decreased significantly. (2) No significant differences were observed in the gas exchange parameters (net photosynthetic rate P_n, stomatal conductance G_s, transpiration rate T_r), chlorophyll fluorescence parameters (photosystem II maximum photochemical efficiency Fv/Fm, actual photochemical efficiency ΦPSII, apparent electron transfer rate ETR) and leaf nutrient contents of both species after 8 years of throughfall reduction. (3) Compared with P. massoniana, the stomatal limitation (L_s) of the C. hystrix was larger and the water use efficiency (WUE) was higher, especially in the dry season.

Conclusion There are differences in the strategies of P. massoniana and C. hystrix to cope with drought stress. P. massoniana responds to drought by adjusting leaf anatomy to produce xeromorphic needles, while C. hystrix is more inclined to adjust stomata (L_s) and improve water use efficiency (WUE) to adapt to drought.