A multi-scale analysis of drought effects on intrinsic water use efficiency in a Mediterranean evergreen oak forest
Résumé
Water use efficiency (WUE), the amount of assimilated carbon per amount of transpired water is central to assess how trees and forests respond to the ongoing climate changes and, particularly, to increasing drought severity. We concurrently evaluated leaf- and ecosystem-scale intrinsic WUE (WUEi) of a Mediterranean evergreen oak (Quercus ilex) forest in southern France using stable carbon isotopic discrimination, leaf gas exchange and eddy covariance fluxes. Nine years of continuous daily eddy fluxes were converted into 7-day composite chronicle of WUEi and then into δ13C input to check, is there a link between eddy and bulk leaf δ13C? The relationship between ecosystem-scale WUEi and water limitation, assessed by the predawn tree potential (ψpd), followed a trapezoidal curve with a plateau value of 158.0 ± 4.0 µmol CO2 mol-1 H2O. WUEi began to decline from -2.4 MPa with gas exchange ceasing at -4.4 MPa. WUEi measured at leaf scale followed a bi-linear relationship with ψpd that peaked at ψpd = -3.15 MPa, reaching 120.5 ± 16.4 µmol CO2 mol-1 H2O. Current year leaf δ13C is linearly related to the averaged δ13C input over the leaf expansion period. In 1-year old leaves, adjustment in bulk δ13C was dependent on the degree of water limitation. Whole-isotopic mass balance at tree or ecosystem scales continue to be a major challenge because large gaps remain in understanding all the processes that influence δ13C of fluxes and C pools.
Auteurs, date et publication :
Auteurs Serge Rambal , Jeannine Cavender-Bares , Jean-Marc Limousin , Yann Salmon
Publication : Agricultural and Forest Meteorology
Date : 2025
Volume : 361
Pages : 110283