With Larix principis-rupprechtii forest in the Xiangshui River sub-basin of the Liupan Mountain area as test material, we monitored sap flow in L. principis-rupprechtii using the thermal diffusion probe during the growing season (from May 13th to September 30th) of 2022 and measured meteorological conditions and soil moisture to explore the water utilization patterns of L. principis-rupprechtii forest under different drought types. The results showed that the piecewise linear function could accurately reflect the variation of the sap flow rate with soil relative extractable water (REW) and vapor pressure deficit (VPD). Based on the thresholds of the piecewise function, the drought conditions in this area were classified into four types: non-drought (REW≥0.37 m3·m-3, VPD<0.99 kPa), atmospheric drought (REW≥0.37 m3·m-3, VPD>0.99 kPa), soil drought (REW<0.37 m3·m-3, VPD<0.99 kPa), and combined drought (REW<0.37 m3·m-3, VPD>0.99 kPa). The average sap flow rate of L. principis-rupprechtii was the highest under atmospheric drought (0.042 mL·cm-2·min-1) and the lowest under soil drought (0.022 mL·cm-2·min-1). The dominant factors influencing the sap flow rate varied across drought types. Under non-drought types, the dominant factors of sap flow were VPD and solar radiation (Rs). Under soil drought, the main influencing factor of sap flow was Rs. Under atmospheric drought and combined drought, the main influencing factors of sap flow were REW and Rs. When facing drought stress, L. principis-rupprechtii would initiate trunk sap flow earlier for trunk water replenishment, with soil moisture as the main limiting factor.
本研究以六盘山区香水河小流域华北落叶松林为对象,于2022年生长季(5月13日—9月30日)利用热扩散探针测定树干液流速率,并同步监测气象条件与土壤水分,探究不同干旱类型下华北落叶松林的水分利用规律。结果表明: 线性分段函数可以准确地反映树干液流速率随土壤相对有效含水率(REW)和饱和水汽压差(VPD)的变化规律,根据分段函数的阈值将该地区干旱情况划分为非干旱(REW≥0.37 m3·m-3,VPD<0.99 kPa)、大气干旱(REW≥0.37 m3·m-3,VPD>0.99 kPa)、土壤干旱(REW<0.37 m3·m-3,VPD<0.99 kPa)和综合干旱(REW<0.37 m3·m-3,VPD>0.99 kPa)4种类型。华北落叶松平均树干液流速率在大气干旱类型下最大(0.042 mL·cm-2·min-1),在土壤干旱类型下最小(0.022 mL·cm-2·min-1)。不同干旱类型下树干液流速率的主导因子不同。非干旱时,树干液流的主要影响因素为饱和水汽压差和太阳辐射;土壤干旱时,树干液流的主要影响因素为太阳辐射;而在大气干旱和综合干旱时,树干液流的主要影响因素为土壤相对有效含水率和太阳辐射。华北落叶松在面临干旱胁迫时会提前启动树干液流进行树干补水,其主要限制因子是土壤水分。.
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