Abstract: We selected two dominant tree species including Tsuga chinensis and Cyclobalanopsis stewardiana grown in the evergreen needle-leaved and broadleaved mixed forest at high-altitude on Mao’er Mountain, and studied their seasonal changes in photosynthetic pigments, net photosynthetic rate(A_max), chlorophyll fluorescence and antioxidative system. T.chinensis and C.stewardiana down-regulated the values of chlorophyll(Chl) content, predawn maximum photochemistry efficiency of PSⅡ(F_v/F_m-predawn), A_max and stomatal conductance(G_s) to the minimum during winter stress. The activities of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT) and the contents of ascorbic acid(AsA), glutathione(GSH) and carotenoids(Car) of C.stewardiana were the highest in winter, which showed good synergy in resisting adverse external environments and scavenging reactive oxygen species(ROS), while only AsA, GSH and Car in T.chinensis maintained good synergy in resisting winter stress. The seasonal changes of MDA contents in T.chinensis and C.stewardiana were correlated with the seasonal variations of environment as well as the seasonal variations of antioxidative enzyme activities and antioxidants accumulation. Therefore, T.chinensis and C.stewardiana had different antioxidant-defense strategies, but the same photosynthetic adaptation strategy was down regulation for winter acclimation.

Key words: photosynthesis, antioxidant system, Tsuga chinensis, Cyclobalanopsis stewardiana, seasonal acclimation, winter stress