整树水力导度协同冠层气孔导度调节森林蒸腾

冠层气孔导度决定森林的蒸腾效率,它对驱动水汽移动的水汽应力的响应受树木水力结构的影响,并随水汽压亏缺上升和水力导度下降而降低,维持水势在最低阈值之上,避免出现水力灾变,调控冠层蒸腾。由于叶形和树冠结构的特点,部分脱耦联反映了湿润地区阔叶林冠层与大气的水汽交换特征,单纯以气孔导度的变化难以完整描述水分通量的调节规律,因而,需要考虑冠层气孔导度与水力导度协同控制冠层蒸腾的潜在机理。通过整合叶片气孔气体交换、树干液流、冠层微气象和其他环境因子的野外观测值,估测不同时间尺度的森林冠层气孔导度与大气的脱耦联系数和变异范围,以基于树干液流的冠层蒸腾,结合叶片/土壤水势梯度计算的水力导度,分析水力导度影响冠层气孔导度响应水汽压亏缺的敏感性,可以揭示和阐明水力导度和冠层气孔导度联合调节森林蒸腾的机理,对准确估测全球变化背景下森林对水资源利用的潜在生态效应有明显的理论意义。

On the coordinated regulation of forest transpiration by hydraulic conductance and canopy stomatal conductance

Canopy stomatal conductance determines transpiration efficiency of forest, and its response to evaporative demand that drives vapor movement is affected by hydraulic architecture. It regulates canopy transpiration by decreasing with increase of vapor pressure deficit and decline of hydraulic conductance in order to maintain water potential above threshold so that the hydraulic breakdown could be avoided. Due to its complex canopy structure and large leaf area in the moisture broadleaf forest, vapor exchanging between canopy and atmosphere is characterized with partial decoupling, leading to the difficulty to describe the regulation of water flux accurately by monitoring the variation of stomatal conductance solely. As a result, it is of necessary to dig further into the underlying mechanism that controlling the canopy transpiration by taking the coordination of stomatal conductance with whole-tree hydraulic conductance into account. One feasible approach, which aims to clarify the underlying mechanism, is to integrate the measurements of gas exchange and sap flow as well as simultaneous recodes of micro-meteorological and other environmental factors. Such integrations will provide the basis for investigating the decoupling coefficients of canopy and atmosphere at multiple temporal scales, as well as figuring out the response of canopy stomatal conductance to vapor pressure deficit by analyzing the hydraulic conductance calculated from sap flow and leaf-soil water potential gradient. It is expected that the elucidation of the coordinated regulation between canopoy stomatal conductance and hydraulic conductance will help to accurately estimate water use of forest in moisture area and potentially can be applied to assess ecological effects of global change on moisture forests.