宁夏河东沙区侧柏冠层气孔导度对环境因子的响应及其模拟

Responses and modeling of canopy stomatal conductance of Platycladus orientalis to environmental factors in Hedong sandy land,Ningxia

为了解林木冠层气孔导度对环境因子的响应规律,进一步阐释冠层气孔导度调控森林蒸腾的机理,本研究以宁夏河东沙区典型防护林树种侧柏(Platycladus orientalis)为对象,利用Granier热扩散技术,在生长旺季(7—9月)连续监测树干液流,并同步观测小气候;利用Penman-Monteith方程计算获得连续的冠层气孔导度(gc),并采用Jarvis-Stewart气孔模型对侧柏冠层气孔导度变化过程进行模拟。结果表明:环境因子与gc呈极显著相关关系(P<0.01),对侧柏gc的影响从大到小依次为大气温度(Ta)>太阳辐射(Rs)>饱和水气压亏缺(VPD)>空气湿度(RH)。典型晴天下,gc与VPD、Ta的关系曲线上升阶段和下降阶段路径不同,呈现"磁滞回环"的特性,且不同时段表现出不同的响应规律。Jarvis-Stewart模型较好地模拟了侧柏冠层气孔导度对环境变量Rs、VPD、Ta的响应过程,采用交叉验证法对模型进行验证和参数率定,可以解释84.4%的变量。

To understand the responses of forest canopy stomatal conductance to environmental factors and the underlying mechanism of canopy stomatal conductance controlling forest transpiration,the Granier thermal dissipation probe technology was used to monitor the sap flow of Platycladus orientalis,a typical tree species of protective forest in Hedong sandy land of Ningxia,from July to September. The microclimate variables were synchronously monitored. Based on sap flow,the continuous canopy stomatal conductance（ gc） was calculated by Penman-Monteith equation.An improved Jarvis-Stewart stomatal model was used for simulating the changes of gc. The results showed that the environmental variables such as saturated vapor pressure deficit（ VPD）,air temperature（ Ta）,relative humidity（ RH） and solar radiation（ Rs） were significantly correlated with gcof P. orientalis（ P〈0.01）. The magnitude of the influence of those factors on gcwere Ta〉Rs〉VPD〉RH. In sunny days,the relationships between gcand VPD and between gcand Tawere characterized by a hysteresis loop,with the response path being different from the rising stage to descending stage. Moreover,those relationships showed different response patterns at different time. The Jarvis-Stewart model performed better in simulating the responses of canopy stomatal conductance to environmental factors Rs,VPD,and Ta. Results from cross validation showed that optimal parameter calibration of this model explained 84.4% of the total variation.