Abstract: Dynamics of concentrations of organic free radicals (OFR), content of Vc and activity of SOD was monitored for overwintering needles of Pinus sylvestris var. mongolica and Picea koraiensis in the Changbai Mountain. It showed that the patterns of variation in concentrations of OFR in needles of Pinus koraiensis differed clearly from all other tree species, which was closely related to the severe photoxidation injury. The maximum peaks of Vc content and SOD activity of needles were found that during winter they played an important role in protecting needles from the injury induced by free radicals. SOD activity of Pinus koraiensis needles was much lower than that of Picea koraiensis, which was probably the important reason for susceptible photoxidation injury in winter. The relations among freezing, light and oxidative stress were discussed in terms of free radicals and scavengers.

Key words: Pinus koraiensis, Picea koraiensis, Organic free radical (OFR), Photoxidation injury, SOD, Vc