Abstract: The physiological and ecological characteristics of the endangered Sinocalycanthus chinensis seedlings with the treatments of simulated acid rain of pH2.5, pH3.5, pH4.5 and pH5.6 (control) were determined and analyzed. The results showed that, in all treatments, the day variation of net photosynthetic rate of S.chinensis was a curve with one peak in July. The mean daily net photosynthetic rate reduced with the increasing of the acidity with significant differences among different treatments. The maximum net photosynthetic rate, light saturation point and the relative chlorophyll content decreased gradually with the increasing of the acidity, while the dark respiration rate and the light compensation point increased gradually with the increasing of the acidity. The apparent quantum yields in the treatments of pH2.5 and pH3.5 were lower that the control, while that in the treatment of pH4.5 was higher than the control. F_v/F_m and F_v/F_o reduced with the increasing of the acidity. The activity of peroxidase and superoxide dismutase, the content of malonydialdehyde and the membrane permeability significantly increased with the increasing of the acidity. The results suggested that simulated acid rain could reduce the photosynthetic capacity and had detrimental effect on the physiological traits of S.chinensis.

Key words: Sinocalycanthus chinensis, photosynthetic physiology, chlorophyll fluorescence parameters, membrane lipid peroxidation, antioxidant enzyme activity