Abstract: In the present study, the effects of spring drought stress on morphology and physiological characteristics of leaves and roots of mature Platycladus orientalis and Robinia pseudoacacia were analyzed and the adaptive strategies of the two tree species under drought stress were compared. The results showed that the proline and soluble protein contents, and SOD and POD activities in leaves of P. orientalis were significantly lower than those in leaves of R. pseudoacacia (P<0.05), but the soluble sugar content and CAT activity in leaves of P. orientalis were significantly higher than those in leaves of R. pseudoacacia under spring drought stress (P<0.05). Meanwhile, the difference in malondialdehyde content in leaves was not significant between P. orientalis and R. pseudoacacia (P>0.05). The proline and soluble protein contents, and POD and CAT activities in roots of P. orientalis were significantly lower than those in roots of R. pseudoacacia (P<0.05). However, the soluble sugar and malondialdehyde contents in roots of P. orientalis were significantly higher than those in roots of R. pseudoacacia (P<0.05). The specific leaf weight and root activity of P. orientalis were significantly higher than those of R. pseudoacacia (P<0.05). The root length density and root area index of R. pseudoacacia were significantly greater than those of P. orientalis(P<0.05). These results indicated that there were differences in permeating substance contents and antioxidative enzyme activities between P. orientalis and R. pseudoacacia under spring drought stress. The damages of spring drought to leaves were similar between P. orientalis and R. pseudoacacia, but the damages were more severe to the roots of P. orientalis. Adult P. orientalis mainly adopted droughttolerance strategies, while mature R. Pseudoacacia mainly adopted droughtavoidance strategies under spring drought.

Key words: growth ring age, climatic factor, radical variation, wood property, Machilus pauhoi