HR: 16:55h
AN: B24C-04 INVITED    [Abstracts]
TI: Ecosystem-level water-use efficiency inferred from eddy covariance data: definitions, patterns and spatial up-scaling
AU: * Reichstein, M
EM: mreichstein@bgc-jena.mpg.de
AU: Beer, C
AU: Kuglitsch, F
AU: Papale, D
AU: Soussana, J A
AU: Janssens, I
AU: Ciais, P
AU: Baldocchi, D
AU: Buchmann, N
AU: Verbeeck, H
AU: Ceulemans, R
AU: Moors, E
AU: Köstner, B
AU: Schulze, D
AU: Knohl, A
AU: Law, B E
AB: In this presentation we discuss ways to infer and to interpret water-use efficiency at ecosystem level (WUEe) from eddy covariance flux data and possibilities for scaling these patterns to regional and continental scale. In particular we convey the following: WUEe may be computed as a ratio of integrated fluxes or as the slope of carbon versus water fluxes offering different chances for interpretation. If computed from net ecosystem exchange and evapotranspiration on has to take of counfounding effects of respiration and soil evaporation. WUEe time-series at diurnal and seasonal scale is a valuable ecosystem physiological diagnostic for example about ecosystem-level responses to drought. Most often WUEe decreases during dry periods. The mean growing season ecosystem water-use efficiency of gross carbon uptake (WUE_GPP) is highest in temperate broad-leaved deciduous forests, followed by temperate mixed forests, temperate evergreen conifers, Mediterranean broad-leaved deciduous forests, Mediterranean broad-leaved evergreen forests and Mediterranean evergreen conifers and boreal, grassland and tundra ecosystems. Water-use efficiency exhibits a temporally quite conservative relation with atmospheric water vapor pressure deficit (VPD) that is modified between sites by leaf area index (LAI) and soil quality, such that WUEe increases with LAI and soil water holding capacity which is related to texture. This property and tight coupling between carbon and water cycles is used to estimate catchment-scale water-use efficiency and primary productivity by integration of space-borne earth observation and river discharge data.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 1600 GLOBAL CHANGE
SC: Biogeosciences [B]
MN: 2007 Fall Meeting