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

Our objective was to quantify the annual soil carbon efflux in a young beach forest in north-eastern France (Hesse Forest, Euroflux site FR02) from measurements of soil CO2 efflux. Soil CO2 efflux exhibited pronounced seasonal variations which did not solely reflect seasonal changes in soil temperature. In particular, strong differences in soil CO2 efflux were observed between sum mer 1996 and summer 1997 while the patterns of soil temperature were similar. This difference is at least partly explained by an inhibition of soil CO2 efflux at low soil water content. Since changes in soil temperature (T) and soil volumetric water content at -10 cm (theta(v)) affect soil CO2 efflux, an empirical model is proposed (y = A q(v) e(BT)) which account for 86 % of the variation in soil CO2 efflux. The difference between two estimates of annual soil carbon efflux (575 g(C) m(-2) year(-1) from June 1996 to May 1997 and 663 g(C) m(-2) year(-1) from December 1996 to November 1997) clearly highlights the dependence of soil carbon efflux on soil water content during summer. ((C) Inra/Elsevier, Paris.).