北京山区侧柏林冠层-大气蒸腾导度模拟及环境因子响应

Simulation and environmental response of canopy-atmospheric transpiration conductance of Platycladus orientalis forests in the Beijing mountain area

蒸腾导度模型是衡量冠层-大气界面水汽输出的重要阻力模型,研究其特征及对环境因子的响应,为揭示森林冠层-大气界面水汽输出阻力机制提供理论依据。以首都圈森林生态系统定位观测研究站侧柏林为研究对象,采用TDP热探针法测定侧柏林树干液流密度,同步监测光合有效辐射、饱和水汽压差、气温、风速等主要环境因子,分析冠层导度和空气动力学导度的动态变化,构建冠层-大气蒸腾导度模型并模拟,明确冠层-大气蒸腾导度对各环境因子的响应关系。结果表明:蒸腾导度季节变化表现为非生长季与冠层导度趋势一致,生长季与空气动力学导度趋势一致,全年均为单峰趋势。冬季蒸腾导度与冠层导度保持较稳定差值(45 mol m^(-2 )s^(-1)左右),其他季节蒸腾导度与冠层导度、空气动力学导度的最大差值,均在各季节冠层导度、空气动力学导度的峰值水平。全年日均蒸腾导度冬季最大(86.92 mol m^(-2 )s^(-1)),其他季节较小且稳定(40—50 mol m^(-2 )s^(-1)之间)。在非生长季各环境因子对蒸腾导度的影响与对冠层导度的影响基本一致,温度为主要影响因子(r=-0.198),其他环境因子影响较小(r<0.1);在生长季中风速为主要影响因子(r=0.488),光合有效辐射(r=0.228)和饱和水汽压差(r=-0.299)的影响明显升高,温度的影响降低(r=0.114)。蒸腾导度模型较好的模拟了冠层-大气界面侧柏蒸腾不同季节的变化规律,阐明了各环境因子和冠层导度、空气动力学导度对蒸腾导度的影响机制,证实在生长季应重视空气动力学导度对蒸腾的影响。

Transpiration conductance model is an important resistance model to measure water vapor output at the canopy atmosphere interface. Our study foucused on its characteristics and response to environmental factors, which provided a theoretical basis for clarifying the water vapor output mechanism at the canopy atmosphere interface. In this paper, Platycladus orientalis forest observation station of forest ecosystem in the capital circle was taken as the research object. Through analyzing the dynamic changes of canopy conductance and aerodynamics conductance by TDP thermoprobe, we measured the density of sap flow in the trunk of Platycladus orientalis forest and monitoring the main environmental factors such as photosynthetic effective radiation, saturated water vapor pressure difference, air temperature, and wind speed. And the model of canopy-atmospheric transpiration conductance was derived and calculated so as to build a simulation, which clarified the response of canopy atmospheric transpiration conductance to various environmental factors. The results showed that the trend of transpiration conductance in non-growing season was consistent with that in canopy;the growing season was consistent with the trend of aerodynamic conductance, and the trend was single peak throughout the year. The difference between transpiration conductance and canopy conductance in winter remained stable(around 45 mol m^(-2 )s^(-1));the maximum difference value among transpiration conductance, canopy conductance and aerodynamic conductance in other seasons was at the peak level of canopy conductance and aerodynamic conductance;the annual average transpiration conductance was the largest in winter(86.92 mol m^(-2 )s^(-1)) and it was smaller and stable in other seasons(40—50 mol m^(-2 )s^(-1));in the non-growing season, the effect of environmental factors on transpiration conductance was basically the same as that on canopy conductance, and temperature was the most important factor(r=-0.198) while other environmental factors had little impact(r<0.1);in the growing season, wind speed was the most important factor(r=0.488);the influence of photosynthetic effective radiation(r=0.228) and vapor pressure deficit(r=-0.299) was significantly increased, and the influence of temperature was reduced(r=0.114). The model of transpiration conductance simulated the change rule of Platycladus orientalis transpiration in different seasons, clarified the influence mechanism of environmental factors, canopy conductance and aerodynamic conductance on transpiration conductance, and confirmed that we should pay attention to the influence of aerodynamic conductance on transpiration in growing season.