在沙地，土壤水分含量微小的变化足以引起树木生理活动的显著改变并对植被稳定性产生重大干扰。如何揭示树木生理活动对沙地土壤水分变化的敏感性及响应机制？过去主要集中在对树木枝叶的生理、形态特征变化的观测，并不能反映树木整体的水分状态，而树干液流集合了与树木生存、生长、繁殖等紧密关联的水分信息。本文以沙地樟子松人工林为研究对象，在前期研究基础上提出假说：对应于土壤水分亏缺驱动下樟子松个体生理活动下降的阶段特征，树干液流日变化依次呈现夜间液流发生、峰值下降与提前、峰值微弱与滞后三个典型特征来响应。为验证该假说，设计田间控水试验，采用热扩散（TDP）与热场形变（HFD）技术联合观测单株液流，以明确樟子松液流随土壤水分亏缺进程而变化的规律，辨析响应节点。结合对叶、土水势的同步观测，判断与液流过程显著变化相对应的土壤水分阈值。研究结果为基于土壤水分含量预判个体生长状况及植被的稳定性提供了可靠、简化的方法。

The little changes in soil moisture in sandy land may cause large effects on the physiological activities of trees. It is therefore significant in theory and practice to quantify the relationships between soil moisture and stability of the stands. Many past attempts to judge growth conditions of a tree by the physiological activities of leaf or changes of the foliage morphological characteristics were not enough to accurately describe water status of the whole tree. However, the sap flow of the trunk can bring information related to survive, growth, reproduction and a set of comprehensive physiological information of a tree. These information can help with judging stability of a individual tree. Therefore, we hypothesize that the diurnal variation of sap flow with the developing of soil moisture deficit shows three typical forms: nocturnal sap flow, declined peak with time forward, weak peak with time lag. To test this hypothesis, two methods of the thermal dissipation probe (TDP) and the thermal field deformation (HFD) have been combined to analyze the characteristics of sap flow of Pinus sylvestris var. mongolica. A water control trial has been designed in field to reveal the rule of diurnal variation patterns of sap flow with soil water deficit, and the sudden changes of physiological activities of a tree will have been diagnosed. The key thresholds of soil water content during the process will have been found by synchronized measurements of leaf water potential and soil water potential. The results is helpful to pre-judge the stability of stands according to the soil moisture, and provide an effective basis for quantifying the vegetation carrying capacity in sandy land according to rainfall resources.