Abstract: With pot experiment, this paper studied the effects of simulated acid rain on the membrane injury, antioxidant enzyme activities, chlorophyll (Chl) content, and gas exchange of Paramecia lotungensis seedlings leaves. The results showed that under simulated acid rain stress, the membrane permeability and malondialdehyde (MDA) content of P.lotungensis leaves increased significantly , and there was a significant correlation between them. The catalase (CAT) activity decreased gradually, while superoxide dismutase (SOD) and peroxidase (POD) activities increased gradually or greatly. Chl content had an obvious decrease, and net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), water use efficiency (WUE), and stomatal limitation value (L_s) all had a decreasing trend. The intercellular CO₂ concentration (C_i) tended to increase. All of these suggested that simulated acid rain induced the production of activated oxygen (O₂^-_·), resulting in the maladjustment of antioxidant enzyme system and the imbalance between O₂^-_· production and elimination, which in turn accelerated lipid peroxidation, damaged membrane permeability, disorganized chlorophyll structure, and decreased photosynthetic rate.

Key words: Flora, Riparian zone, Community, Plant, Changbai Mountain