Effects of Water Stress on Seedling Growth and Biomass Allocation of Toona ciliata var. pubescens

Toona ciliata var. pubescens is a native and widespread dominant deciduous broad-leaf tree in the subtropical region of China. An experiment was conducted to investigate the effect of water stress on the growth,biomass partition and root characteristic index of 1-year-old T. ciliata var. pubescens seedlings. The seedlings grew under well-watered and water stressed conditions which were imposed by controlling the water supply. The results showed that the water stress had a negative significant effect on the root growth,but no effect on the growth of ground diameter was found. The root mass ratio increased in the beginning,and then decreased. The leaf mass ratio increased at the early and medium water stress period,and decreased at later and terminal water stress period. The shoot mass ratio increased from beginning to end. The average root diameter decreased gradually from the medium to the later water stress period,and then increased at terminal water stress period. However,the ratio of fine root to total root length increased gradually from the medium to the later water stress period,and then decreased at terminal water stress period. The water stress has a significant effect on the root tip numbers. Therefore,the water supply is satisfied with the aboveground organ growth demand as the priority at the cost of limiting root growth under the water stress conditions. Defoliation and the secondary root growth were used to alleviate water stress pressure and improve water absorption efficiency.