Geography

Temporal and among-site variability of inherent water use efficiency at the ecosystem level

Document Type

Article

Abstract

Half-hourly measurements of the net exchanges of carbon dioxide and water vapor between terrestrial ecosystems and the atmosphere provide estimates of gross primary production (GPP) and évapotranspiration (ET) at the ecosystem level and on daily to annual timescales. The ratio of these quantities represents ecosystem water use efficiency. Its multiplication with mean daylight vapor pressure deficit (VPD) leads to a quantity which we call "inherent water use efficiency" (IWUE*). The dependence of IWUE* on environmental conditions indicates possible adaptive adjustment of ecosystem physiology in response to a changing environment. IWUE* is analyzed for 43 sites across a range of plant functional types and climatic conditions. IWUE* increases during short-term moderate drought conditions. Mean annual IWUE* varied by a factor of 3 among all sites. This is partly explained by soil moisture at field capacity, particularly in deciduous broad-leaved forests. Canopy light interception sets the upper limits to canopy photosynthesis, and explains half the variance in annual IWUE* among herbaceous ecosystems and evergreen needle-leaved forests. Knowledge of IWUE* offers valuable improvement to the representation of carbon and water coupling in ecosystem process models. Copyright 2009 by the American Geophysical Union.

Publication Title

Global Biogeochemical Cycles

Publication Date

6-1-2009

Volume

23

Issue

2

ISSN

0886-6236

DOI

10.1029/2008GB003233

Keywords

gross primary production, inherent water use efficiency, coniferous forests, photosynthesis, deciduous forests, plants, primary productivity, ecosystems, water vapor, vegetation, evapotranspirationm, temporal variation, carbon dioxide, wetlands, grasslands, forest ecosystems, water use efficiency, gas exchange

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