HR: 1340h
AN: B33E-1659    [Abstracts]
TI: Water-use efficiency at different scales and its between-site variability
AU: * Beer, C
EM: cbeer@bgc-jena.mpg.de
AF: Max Planck Institute for Biogeochemistry, Hans Knoell Str 10, Jena, 07745, Germany
AU: Reichstein, M
EM: mreichstein@bgc-jena.mpg.de
AF: Max Planck Institute for Biogeochemistry, Hans Knoell Str 10, Jena, 07745, Germany
AU: Buchmann, N
EM: nina.buchmann@ipw.agrl.ethz.ch
AF: ETH Zürich, Universitaetstrasse 2, Zürich, 8092, Switzerland
AU: Law, B
EM: bev.law@oregonstate.edu
AF: Oregon State University, Corvallis, Oregon, 97331, United States
AU: Knohl, A
EM: alexander.knohl@ipw.agrl.ethz.ch
AF: ETH Zürich, Universitaetstrasse 2, Zürich, 8092, Switzerland
AB: The eddy covariance technique is widely applied for estimating the carbon and water exchanges between terrestrial ecosystems and the atmosphere, and also gross primary productivity can be reliably derived from such measurements. With such data we study intrinsic water-use efficiency (iWUE) at ecosystem scale that is the ratio between GPP and stomatal conductance which can be approximated as the ratio between GPP times VPD and evapotranspiration. Effects of LAI on iWUE in deciduous forests and grasslands during the growing season are detected. This effect is explained by combined impacts of light absorption on photosynthesis and bare soil evaporation. Increasing iWUE under drought conditions found at leaf level is partly confirmed at ecosystem scale at daily resolution, but the effect is small. At longer time scales, however, other ecosystem processes are suggested to override the impact of stomatal conductance on iWUE. This hypothesis is based on the pronounced between-site variability of iWUE (replacement of time by space), and on specific relationships of mean annual iWUE to environmental conditions. Besides the impact of maximum LAI, mean annual iWUE relates to both plant- available water-holding capacity of the soil (WHC) and mean annual soil moisture. Carbon isotope ratios independently confirm these findings. The first potential explanation of increasing iWUE with WHC, high nitrogen availability, is rejected by the anti-correlation between mean annual iWUE and leaf-nitrogen content. Rather, memory effects of droughts on maximum carbon assimilation are suggested to explain this observation. Mean annual iWUE of herbaceous ecosystems is lower than that of forests, and deciduous broad-leaved forests mostly show higher mean annual iWUE values than evergreen needle-leaved forests. Presented relationships of mean annual iWUE at ecosystem scale to different ecosystem properties can be further used to extrapolate mean annual iWUE in space for deriving global maps as the basis for further diagnosis and evaluation of ecosystem models.
DE: 0428 Carbon cycling (4806)
DE: 0434 Data sets
DE: 0476 Plant ecology (1851)
DE: 0480 Remote sensing
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting