黑河下游影响荒漠河岸胡杨林蒸腾的冠层与大气耦合分析

Coupling Analysis between Canopy and Atmosphere that Influenced Transpiration of a Populus Euphratica Oliv. Forest in the Lower Reach of Heihe River

基于2014年胡杨主要生长季内树形特征、树干液流、环境因子的实际观测数据,利用经验公式,计算了胡杨冠层蒸腾速率、冠层气孔导度与解耦系数的值,分析了其日变化与季节变化特征。结果表明:(1)从日变化趋势来看,解耦系数在早晨和傍晚时较小,中午达到最大值,这主要是由于早晨和傍晚时太阳辐射比较弱、作物气孔开度小,使冠层气孔导度降低造成的;而中午时冠层气孔导度达到全天的最大值,解耦系数值也达到最大。(2)从季节变化趋势来看,解耦系数与冠层气孔导度变化趋势相近,在生长季内均呈先增大后减小,之后略有浮动增大,最后减小的趋势。本研究对影响荒漠河岸胡杨林蒸腾的冠层与下层大气进行相关性推断,认为影响胡杨林蒸腾的冠层与大气耦合度较高。尽管试验地处于极端干旱区,下层大气十分干燥,林冠层叶气界面水分散失很快,但黑河下游河岸林供水良好,林冠层空气动力学条件相近,使得胡杨林蒸腾主要受叶面气孔控制。

The degree of coupling between the plant canopy and atmosphere indicates the exchanging ability of momentum, energy and mass between the two systems. Based on the measured data of tree characteristics, sap flow and environmental factors in 2014 and the empirical formulae, we calculated the transpiration rate, stomatal conductance and decoupling coefficient of the canopy, and analyzed the diurnal and seasonal features of all the three parameters. Results indicated that： （ 1 ） the value of decoupling coefficient peaked at noon and minimized in the morning and evening, and this is mainly due to the weak radiation and lower stomatal conductance in the morning and evening. However, the canopy stomatal conductance peaked at noon, and the value of decoupling coefficient maximized accordingly. （2） The seasonal variation of the decoupling coefficient is similar to that of the canopy stomatal conductance. It increased at first and then decreased, then increased slightly and decreased at last. We inferred the correlation between the canopy of the Populus euphratica forest and atmosphere, result showed that the canopy of P. euphratic was highly coupled with the atmosphere. Though our study area is located in the Ejin oasis where is extremely dry, the supplement of the surface water from the upstream of Heihe River ensured the water that P. euphratica needed. The water and aerodynamic status are both good, and the transpira- tion is mainly controlled by stom^t.