中文摘要：

蒸腾是植物重要的生理活动之一,受到多个环境要素的综合影响。该文利用热平衡包裹式茎干液流仪Flow32监测系统,对河西走廊中段绿洲—荒漠过渡带主要固沙植物梭梭（Haloxylon ammodendron）生长季的蒸腾过程进行连续监测,并分析了其对环境要素的响应。结果表明：（1）梭梭茎干液流速率随枝直径的增加而增加,液流密度随枝直径的增加而降低,梭梭液流密度日变化呈多峰特征,整个生长季液流密度变化比较稳定。（2）主成分分析表明第1、2、3主成分能够分别解释环境信息49%、15%、12%的变化,第一主成分中水汽压亏缺、光合有效辐射及气温反映了大气的蒸腾需求。（3）S型模型对液流密度日变化模拟精度达到0.86,考虑时滞效应后模拟精度提高至0.9,降水天气条件下模拟精度降低至0.65。（4）液流密度对主要环境要素存在非对称响应,同光合有效辐射呈逆时针环状,同水汽压亏缺、蒸腾需求指数呈顺时针环状。

英文摘要：

Aims Transpiration is one of important physiological activities for plants, which is regulated by many environmental variables. Our objectives were to understand the responses of sap flow density ofHaloxylon ammodendronto environ-mental variables and simulate its diurnal change under different micrometeorological conditions. MethodsSap flow in stems ofH. ammodendronwas measured with stem heat balance method using commercial sap-flow gauges from May to October, 2014, in the oasis-desert ecotone, located in the middle range of Hexi Corridor, Northwestern China. Important findingsSap flow velocity ofH. ammodendronexhibited a positive relationship with stem diameter, but sap flow density （Js） decreased with stem diameter. The first three axes of principal component analysis （PCA） ex-plained 49%, 15%, 12% of variances in the environmental datasets, respectively, and vapour pressure deficit （VPD）, photosynthetically active radiation （PAR）, temperature in the first axes indicated the atmospheric evaporative demand. A sigmoid function could explain 86% of the variation inJsin typical sunny days, while only 65% onrainy days. It was worth noting the simulatedJsusing the established sigmoid function agreed well with the measurements （R2 = 0.90） if the time lags ofJs to principle environmental variables were taken into consideration. Plots of 30-minJs againstPAR, VPD, and evaporative demand index （EDI） revealed a counter-clockwise hysteresis forPAR, but a clockwise hysteresis forVPD andEDI, it was possibly affected by water stress and time lags of sap flow density to principle environmental variables.