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DAAD - Procope Programm: Disturbance of ecosystem respiration measurements in forests by diurnal fluctuations of the volatile soil Carbon stock

The volatile Carbon stock of soils, i.e. the storage that underlies short term changes, includes the gaseous CO2 present in the soil air and the dissolved CO2 in the water. This stock is marginal in contrast to the carbon stored in soil organic matter or in the biomass, however, it can amount up to several times the daily ecosystem respiration and can be equivalent to the CO2 content of an atmospheric air column of more than 50 m. Therefore ecosystem CO2 exchange measurements interfere with soil stock changes, i.e. an CO2 efflux is not necessarily the result of an actual production and soil CO2 production can also be masked by accumulating CO2 in the soil. The time scales of the volatility of soil CO2 can be seasonal (e.g. summer filling the subsoil with CO2 when respiration is high, depletion in winter when respiration rates are low), multi-daily (e.g. stock filling after rainy period by impeded top-soil diffusion ) and hourly (e.g. by the diurnal temperature cycle causing a extension and compression of the soil-air column ). To benefit from the complementary methodological and scientific experience and in order to support the collaboration of young scientist of different institutes and research areas a cooperation project was established. Partners in this project are the Institute of Soil Science of the University of Freiburg and the UMR Ecologie et Ecophysiologie forestiere of the INRA in Champenoux. The project is funded by the DAAD Procope program. As Partners The central goal of the project is to reveal possible discrepancies between soil CO2 efflux and soil respiration, i.e. the actual production of CO2. We hypothesize, that soil respiration models are significantly improved when the efflux rates are corrected for changes of the volatile carbon stock. As test sites two complementary forest sites were chosen. A deeply aerated sandy/gravely soil at Hartheim,Germany, and a loamy site with stagnic subsoil and limited aerated at Hesse, France. Following subgoals will be treated: characterization of the gas transport properties of the sites and the spatial and temporal variability. quantification of diurnal fluctuations of soil CO2 at the two forest sites identification of environmental (weather and site) factors controlling these fluctuations development and implementation of a soil gas transport model to include short-term stock changes in respiration models revealing relationships between the d13C-signature of soil gases CO2 efflux and the soil CO2 stock changes. vertical partitioning of the volatile soil carbon sources by a combined approach of d13C characteristics of the soil air and the efflux and a Fick's law modelling of gas transport.

Ansprechpartner: Helmer Schack-Kirchner
Tel: +49-(0)761-203-3612
Email: helmer.schack-kirchner@bodenkunde.uni-freiburg.de
Projektbeginn: 2009
Projektende: 2010
Schack-Kirchner H

Albert-Ludwigs-Universität Freiburg
Professur für Bodenökologie
Prof. Dr. Lang
Bertoldstr. 17
79098 Freiburg i. Br.

Telefon: +49 761 203 3625
Fax: +49 761 203 3618
Email: fritzi.lang@bodenkunde.uni-freiburg.de
Bernard Longdoz, INRA - Nancy
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