Soil CO2 efflux rates in different tropical vegetation types in French Guiana

Abstract

Soil CO2 efflux rates were measured from July to September 1994 in three vegetation types (primary forest, hardwood plantation and clear-cut) near Sinnamary, French Guiana (5°15' N, 52°55' W), using a portable closed-chamber infrared gas analysis system. Mean soil CO2 efflux rates were: 2.3 μmol m-2 s-1 in the primary forest versus 2.5 μmol m-2 s-1 in the clear-cut and 2.9 μmol m-2 s-1 in the plantation. Diurnal patterns of soil CO2 efflux in the primary forest and hardwood plantation did not show significant (P ≤ 0.05) changes. No correlation between soil CO2 efflux rate and soil temperature was detected in these two vegetation types. In the clearcut, a very pronounced peak in soil CO2 efflux rate occurred, which was strongly correlated with soil temperature. In all three sites, the range of average soil CO2 efflux rates among collars (spatial differences) largely exceeded the range observed among daily means (temporal variation). We investigated the correlation between soil CO2 efflux and several biotic or abiotic variables: soil temperature, water content of upper soil, root density, litter quantity, carbon content and C/N ratio. The only variable that was significantly correlated with the spatial variations in soil CO2 efflux was root density.