Quantifying Stomatal Canopy Conductance in a Pine Forest During Drought from Combined Sap Flow and Canopy Surface Temperature Measurements
Precise determination of stomatal conductance (gs) is important to quantify and predict plant water loss and its response to changing environmental conditions. In this study, we combined measurements of leaf-to-air vapour pressure difference (DL) derived from canopy surface temperature, and transpiration to calculate canopy gs in a pine forest at the ICOS site FR-Bil. The period covered was characterized by two consecutive droughts when tree transpiration was significantly reduced. The inversion of the generalised water transport equation (GT), along with its simplified version, were used to calculate canopy gs that was compared with gs determined from the inversion of the Penman-Monteith (PM) equation. A thermal infrared camera proved to be a reliable tool to continuously monitor canopy temperature and assess DL . On average a 0.3°C temperature difference was found between the canopy and its surrounding air, with values ranging from -2°C to +5°C depending on the time of day, soil moisture and humidity. The three methods used to calculate gs were in agreement, although substantial differences were found under small water stress. However, applying the PM inversion to the whole ecosystem using eddy-covariance fluxes generated gs values that were more than twice as high as those estimated from tree sap-flow. Canopy to air temperature differences led to substantial discrepancies between DL and air saturation vapour pressure deficit at 8 m in the crown (D8), which tended to underestimate gs calculated with the GT method under dry soil and high D8 , and with less of an effect using the PM method. Understorey evapotranspiration estimated from the difference between eddy-covariance and tree transpiration was sustained even during severe droughts. The contrasted behaviour of the trees and the understorey under water stress limits the use of above canopy flux measurements to quantify the response of surface conductance to environmental drivers
Year of publication: |
[2022]
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Authors: | Taborski, Tom ; Domec, Jean-Christophe ; Chipeaux, Christophe ; Lafont, Sebastien ; Wingate, Lisa ; Loustau, Denis |
Publisher: |
[S.l.] : SSRN |
Subject: | Dürre | Drought | Forstwirtschaft | Forestry | Messung | Measurement | Klimawandel | Climate change |
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