Abstract: To know whether winter desiccation injuries of Pinus sylvestris var.mongolica occur in the semi -arid region of eastern Inner-mongolia,dynamics of needles'water content and transpiration rate of its seedlings planted in Spring and Autumn are monitored during overwintering period,and needles critical water content and symptoms of winter desiccation injuries are determined and simulated in laboratory.The results show that the needles'water content of seedlings planted in Autumn becomes significantly lower than their critical water content since January, while that of seedlings planted in Spring has a significantly higher water content than the critical value through the winter,which is beneficial to overwintering.The comparison of water content and transpiration rate indicates that there must have some water incomes for needles even in the soil frozen period.The simulated winter desiccation injury symptoms are similar to those occured on Autumn -planted seedlings in the field,but not observed on Spring-planted ones.It'S concluded that in this region,winter desiccation injuries may not occur in living seedlings planted in Spring.

Key words: Pinus sylvestris var.mongolica, Winter injuries, Winter desiccation