How do leaf and ecosystem measures of water-use efficiency compare?
2017
Medlyn, Belinda E. | de Kauwe, Martin G. | Lin, Yan-Shih | Knauer, Jürgen | Duursma, Remko A. | Williams, Christopher A. | Arneth, Almut | Clement, Rob | Isaac, Peter | Limousin, Jean-Marc | Linderson, Maj-Lena | Meir, Patrick | Martin-StPaul, Nicolas | Wingate, Lisa | Hawkesbury Institute for the Environment [Richmond] (HIE) ; Western Sydney University | Department of Biological Science ; University of Denver | Ecologie et Ecophysiologie Forestières [devient SILVA en 2018] (EEF) ; Institut National de la Recherche Agronomique (INRA)-Université de Lorraine (UL) | Department of Biogeochemical Integration [Jena] ; Max Planck Institute for Biogeochemistry (MPI-BGC) ; Max-Planck-Gesellschaft-Max-Planck-Gesellschaft | Graduate School of Geography ; Clark University | Institut für Meteorologie und Klimaforschung - Atmosphärische Umweltforschung (IMK-IFU) ; Karlsruhe Institute of Technology = Karlsruher Institut für Technologie (KIT) | School of Geosciences ; Monash University [Clayton] | OzFlux ; The University of Queensland (UQ [All campuses : Brisbane, Dutton Park Gatton, Herston, St Lucia and other locations]) | Centre d’Ecologie Fonctionnelle et Evolutive (CEFE) ; Université Paul-Valéry - Montpellier 3 (UPVM)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-École Pratique des Hautes Études (EPHE) ; Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [Occitanie])-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro) | Université de Montpellier (UM) | Centre National de la Recherche Scientifique (CNRS) | Department of Physical Geography and Ecosystem Science [Lund] ; Skane University Hospital [Lund] | Research School of Biology ; Australian National University (ANU) | Ecologie des Forêts Méditerranéennes (URFM) ; Institut National de la Recherche Agronomique (INRA) | Interactions Sol Plante Atmosphère (UMR ISPA) ; Institut National de la Recherche Agronomique (INRA)-Ecole Nationale Supérieure des Sciences Agronomiques de Bordeaux-Aquitaine (Bordeaux Sciences Agro) | ARC Discovery Grant DP120104055,Terrestrial Carbon Program (DE-FG02- 04ER63917 and DE-FG02-04ER63911) | European Project: 609398,EC:FP7:PEOPLE,FP7-PEOPLE-2013-COFUND,AGREENSKILLSPLUS(2014)
The terrestrial carbon and water cycles are intimately linked: the carbon cycle is driven by photosynthesis, while the water balance is dominated by transpiration, and both fluxes are controlled by plant stomatal conductance. The ratio between these fluxes, the plant water-use efficiency (WUE), is a useful indicator of vegetation function. WUE can be estimated using several techniques, including leaf gas exchange, stable isotope discrimination, and eddy covariance. Here we compare global compilations of data for each of these three techniques. We show that patterns of variation in WUE across plant functional types (PFTs) are not consistent among the three datasets. Key discrepancies include the following: leaf-scale data indicate differences between needleleaf and broadleaf forests, but ecosystem-scale data do not; leaf-scale data indicate differences between C3 and C4 species, whereas at ecosystem scale there is a difference between C3 and C4 crops but not grasslands; and isotope-based estimates of WUE are higher than estimates based on gas exchange for most PFTs. Our study quantifies the uncertainty associated with different methods of measuring WUE, indicates potential for bias when using WUE measures to parameterize or validate models, and indicates key research directions needed to reconcile alternative measures of WUE.
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