Soil CO2 efflux in a beech forest: dependence on soil temperature and soil water content

Notre objectif etait de quantifier le flux annuel de carbone provenant du sol d'une jeune hetraie du nord-est de la France (Foret de Hesse, site Euroflux FR02) a partir de mesures de flux de CO 2 provenant du sol. Le flux de CO 2 provenant du sol montre de fortes variations saisonnieres qui ne s'expliquent pas uniquement par des variations saisonnieres de temperature du sol. En particulier, de fortes differences de flux de CO 2 provenant du sol ont ete observees entre l'ete 1996 et l'ete 1997 alors que la temperature du sol etait similaire. Cette difference s'explique au moins en partie par une inhibition du flux de CO 2 provenant du sol lorsque la teneur en eau du sol decroit. Comme les changements de temperature du sol (T) et d'humidite volumique a -10 cm (θ v ) affectent le flux de CO 2 provenant du sol, un modele empirique (y = A θ v e BT ) expliquant 86 % de la variation du flux de CO 2 provenant du sol est propose. La difference entre deux estimations du flux de carbone provenant du sol (575 g C m -2 an -1 de juin 96 a mai 97 et 663 g C m -2 an -1 de dec. 96 a nov. 97) montre clairement les effets de l'humidite du sol pendant l'ete sur le flux de carbone provenant du sol.

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