On the coordinated regulation of forest transpiration by hydraulic conductance and canopy stomatal conductance
整树水力导度协同冠层气孔导度调节森林蒸腾

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.