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冠层气孔导度是生态水文学研究中的一个重要参数,研究其对环境因子的响应,能为建立机理性的森林蒸腾模型提供理论依据。本文利用热扩散探针,于2005年5—9月,测定了六盘山叠叠沟小流域华北落叶松人工林树干液流及其同步的环境因子,计算了林分冠层平均气孔导度(gc)并构建了Jarvis形式的冠层平均气孔导度模型,分析了gc对光合有效辐射(PAR)、空气水汽压亏缺(DVP)和土壤相对有效含水率(REW)的响应。结果表明:该模型能有效地计算gc的日变化特征,计算与观测的gc决定系数R2为0.76(n=952)。gc对各环境因子有不同响应关系,并表现为非线性特征。其中PAR是gc的驱动因子,当PAR<0.35mmol·m-2·s-1时驱动作用明显,大于此值则驱动作用变小;DVP是gc的限制因子,随着DVP的增加gc降低;REW=41%是gc对土壤水分响应的一个关键阈值,当REW>41%时,土壤水分对gc的影响较小,当REW<41%时,土壤水分则成为gc的限制因子。
Canopy stomatal conductance is an important parameter in the research of ecohydrology. Studying its response to environmental factors can provide a theoretical basis for establishing a mechanistic model of forest transpiration. In this paper, the thermal diffusivity probe was used to measure the sap flow and its synchronous environmental factors in the Larix principis-rupprechtii plantation in the Shuidiegou small watershed of Liupan Mountains from May to September in 2005. The average stomatal conductance gc) and constructed the Jarvis-type canopy mean stomatal conductance model and analyzed the response of gc to photosynthetically active radiation (PAR), air-vapor pressure deficit (DVP) and soil relative effective moisture content (REW) The results show that the model can effectively calculate the diurnal variation of gc, and the calculated and observed gc coefficient of determination R2 is 0.76 (n = 952). gc has a different response to environmental factors and behaves as a non-linear feature. PAR was the driving factor of gc, and the driving effect was obvious when PAR <0.35mmol · m-2 · s-1, and the driving effect was smaller than this value. DVP was the limiting factor of gc and decreased with the increase of DVP. REW = 41% is a critical threshold for gc response to soil moisture. When REW> 41%, soil moisture has little effect on gc. When REW <41%, soil moisture becomes a limiting factor for gc.