Abstract: Overwinter experiment of potted and solar-exposed seedlings showed that Pinus koraiensis sustained most severe injury, Pinus sylestris var, mongolica sustained much less, while Picea koraiensis did not show any irreversible damage, ESRsignals of organic free-radicals(OFR) were detected from needle pieces in dark or under 1200 μmol m^-2s^-1 PFD at various temperatures in May: 1) the more severe the winter injury, the more OFRwere produced; 2) the OFRproduction increased with lowering temperature; 3) strong illumination apparently enhanced the OFRproduction; and 4) as a free-radical scavenger,vitamine Cinhibited the OFRproduction, It is suggested that the winter injury of Korean pine seedlings is related to the action of overloaded OFRand the high production of OFRin the field is dependent on strong solar radiation and low temperature.

Key words: ESR, Vitamine C, Conifers, Winter photooxidation