臭椿树干液流和直径微变化对土壤水分的响应

目的] 研究不同水分条件下〔土壤体积含水量分别为10%～15%(W₁)，15%～20%(W₂)，20%～25%(W₃)，25%～30%(W₄)4种水分处理〕臭椿的树干液流和树干径向变化特征及其与气象因子的关系，为深入了解臭椿水分利用策略和科学制定臭椿水分管理措施提供科学依据。方法] 采用热扩散式探针法(TDP)对臭椿树干液流进行连续观测，使用树干径向变化记录仪持续监测臭椿树干直径变化，并同步监测相关环境因子的变化。结果] 在W₃和W₄土壤水分处理下，臭椿液流量基本相同，且树干直径的增长量和变化幅度也相近；在W₁—W₃范围内，臭椿液流量随土壤含水量的增加而增大，但夜间液流占日总液流量的比例随土壤含水量的增加而减小，分别为：W₁(12.3%)>W₂(11.9%)>W₃(6.0%)。日尺度下臭椿树干直径的变化幅度随着土壤含水量的增加而减少，但生长量随之增加；随着土壤含水量的不断增加，白天树干液流与气象因子的相关性呈增大趋势，夜间呈降低趋势；树干液流和树干直径的变化都滞后于太阳辐射，提前于饱和水气压差，且二者与饱和水汽压差之间的时滞均随土壤含水量的增加而减小，但二者与太阳辐射之间的时滞受土壤含水量变化的影响很小。日尺度下臭椿树干液流与树干直径的变化呈反向变化规律，且液流的变化总是提前于树干直径的变化。随着土壤含水量的增加，时滞缩短。结论] 臭椿树干液流与树干直径变化对土壤水分变化的响应存在紧密联系。在W₃水平，土壤含水量达到了臭椿可以充分利用的阈值，因此W₃土壤水分处理为臭椿最适宜的灌溉标准。

Responses of Stem Sap Flow and Diameter of Ailanthus Altissima to Soil Moisture

Objective] In order to understand the water use strategy of Ailanthus altissima and to formulate efficient water management measures for A. altissima, we investigated the characteristics of sap flow and radial stem variation of A. altissima under four volumetric soil moisture content treatments10%~15% (W₁), 15%~20% (W₂), 20%~25% (W₃), and 25%~30% (W₄)] and their relationships with meteorological factors.Methods] Thermal diffusion probes (TDP) were used to continuously observe sap flow, and radial stem change recorders were used to monitor changes in stem diameter of A. altissima. Changes in related environmental factors were simultaneously monitored.Results] Sap flow was almost the same, and growth rate and variation of stem diameter were similar for the W₃ and W₄ treatments. Sap flow increased with increasing soil moisture in the range of W₁ to W₃, whereas the proportion of nighttime sap flow to total daily sap flow showed the opposite trendW₁ (12.3%)>W₂ (11.9%)>W₃ (6.0%)]. Variations in the stem diameter of A. altissima at the daily scale decreased with increasing soil moisture, but the growth rate increased accordingly. The correlation between sap flow and meteorological factors increased with increasing soil moisture content during the daytime, but decreased at night. Changes in both sap flow and stem diameter lagged behind solar radiation and ahead of vapor pressure deficit (VPD), and the time lag between these two indicators and VPD decreased with increasing soil moisture, while the time lag between both and solar radiation was little affected. Changes in sap flow and stem diameter of A. altissima at the daily scale showed an inverse change pattern, and the changes in sap flow always preceded the changes in stem diameter, and the time lag shortened as soil moisture increased.Conclusion] Changes in sap flow and stem diameter of A. altissima to soil moisture changes were closely related. The soil moisture threshold value at which A. altissima could fully utilize soil moisture was the W₃ level. Therefore, the W₃ soil moisture treatment is the most suitable irrigation threshold for A. altissima.