樟子松幼苗水力结构参数和生长特征对模拟降水梯度的响应

水分是影响樟子松生长和存活的关键因素，为弄清樟子松幼苗对水分胁迫的响应过程，采用人工控制降水处理方法 (105%年均降水量：500 mm，无干旱; 74%年均降水量: 350 mm，轻度干旱；42%年均降水量: 200 mm，干旱)，监测了2 a生樟子松幼苗水力结构和生长特征对降水处理的响应。结果表明：随着降水量减少，幼苗水分饱和亏缺没有发生显著变化；轻度干旱下幼苗组织密度显著增加，干旱下幼苗失水系数显著降低；表明樟子松幼苗的保水、抗旱能力随干旱胁迫程度增强而增加。干旱胁迫显著降低了株高、基径和各器官生物量的增加量，轻度干旱胁迫下幼苗根重比和根冠比显著增加，表明轻度干旱胁迫改变了生物量分配格局，促使幼苗向有利于水分维持方向的发展策略；与轻度干旱相比，干旱胁迫下幼苗生物量分配策略并没有发生明显变化。樟子松幼苗可以通过改变水力结构特征和生物量分配策略来适应轻度干旱；而在干旱下幼苗仅改变水力结构特征，不利于其在干旱环境下生存。

Response of Hydraulic Structure Parameters and Growth of Pinus sylvestris var. mongolica Seedling to Simulated Precipitation Gradient

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.