Partitioning evapotranspiration across gradients of woody plant cover: Assessment of a stable isotope technique

Abstract

ABSTRACT: In water‐limited ecosystems, partitioning ecosystem‐scale evapotranspiration fluxes between plant transpirationand soil/canopy evaporation remains a theoretical andtechnical challenge. We used the Biosphere 2 glasshouseto assess partitioning of evapotranspiration across anexperimentally manipulated gradient of woody plant coverusing continuous measurements of near‐surface variationsin the stable isotopic composition of water vapor (d2H).Our technique employs a newly‐developed laser‐basedisotope analyzer and the Keeling plot approach for surfaceflux partitioning. The applicability of the technique wasverified by comparison to separate, simultaneous lysimeterand sap flow estimates ofETpartitioning. The resultsshowed an expected increase in fractional contribution oftranspiration to evapotranspiration as woody coverincreased—fromT/ET=0.61at25%woodycovertoT/ET=0.83 at 100% cover. Further development of this techniquemay enable field characterization of evapotranspirationpartitioning across diverse woody cover gradients, a centralissue in addressing dryland ecohydrological responses toland use and climate change.