Abstract: Fouryearold Phellodendron amurense Rupr. seedlings were exposed to four levels (40 (CK), 80, 120, and 200 nmol·mol^-1) of O₃ in opentop champers (OTCs). The changes in photosynthetic pigment contents, net photosynthesis rate, lipid peroxidation and the activity of antioxidative enzymes were periodically measured in leaves of P. amurense. The results showed that with the increasing O₃ concentration and exposure time, total chlorophyll (Chl) contents, carotenoid (Car) contents and net photosynthesis rate (P_n) were significantly decreased by 52.76%, 44.57% and 54.67%, respectively (P<0.05); electrolyte leakage and malondialdehyde (MDA) contents were significantly increased by 101.49% and 70.21%, respectively (P<0.05). When the O₃ concentration was 80 nmol·mol^-1, the maximum photochemical efficiency (F_v/F_m) had no significant change, while a significant decrease in F_v/F_m was observed when the O₃ concentration was increased to 120 or 200 nmol·mol^-1, showing a significant harm of photosynthetic system function by high O₃ concentrations. Superoxide dismutase (SOD) activity increased at the first fourteen days exposure and then decreased by 17.22%. Compared with CK, the superoxideanion (O₂^-_·) content increased significantly (P<0.05) when the O₃ concentration was 120 or 200 nmol·mol^-1, while only increased significantly in the seventh day  when the O₃ concentration was 80 nmol·mol^-1. It is concluded that P. amurense can tolerate moderately high concentrations of O₃ for a period which is related to its antioxidative ability. Higher O₃ concentrations or longer exposure would incur harm to the photosynthetic system of the leaves.

Key words: index system, green development, Jiangxi Province, regionalization