Abstract: Water plays a key role in affecting the survival and growth of Pinus sylvestris var. mongolica  (MP) on sandy 1and. In order to understand the response of MP seedlings to water stress, in this study the responses of hydraulic structure and growth parameters of 2yearold MP seedlings to the stimulated precipitation gradients at three levels (105% mean annual precipitation: 500 mm, without drought stress, P1; 74% mean annual precipitation: 350 mm, moderate drought stress, P2; and 42% mean annual precipitation, 200 mm, drought stress, P3) were investigated. The results showed that the water saturated deficit of the seedlings was not changed with the decrease of precipitation, tissue density of the seedlings was significantly increased under P2, and the coefficient of water loss of seedlings was significantly decreased under P3. These revealed that the droughtresistance and waterholding capability of the seedlings were increased with the increase of drought stress. Height and base diameter increment of MP plants and biomass accumulation of organs were restricted by drought stress. The root weight ratio and rootshoot ratio were significantly increased under P2, which revealed that the biomass allocation pattern was altered under P2, and the waterholding capability of the seedlings were promoted. Compared with the situation under P2, the biomass allocation of the seedlings was not changed under P3. In conclusion, the hydraulic structure and biomass allocation of MP seedlings could be changed under P2, but only the hydraulic structure could be changed under P3, which was disadvantageous for the survival of MP seedlings in arid environment.

Key words: Pinus sylvestris var. mongolica , seedling, hydraulic structure, precipitation gradient, drought resistance, biomass, root-shoot ratio