SEASONAL-VARIATION OF N2O FLUXES AT A TROPICAL SAVANNA SITE - SOIL CONSUMPTION OF N2O DURING THE DRY SEASON

Soil fluxes of N2O were measured during the dry season in a scrub-grass savannah and in a nearby semideciduous forest in the savannah climatic region of Venezuela. In contrast with a significant emission recorded previously in the rainy season, during the dry season a net consumption of -2.6 +/-2.7x10(9) N2O molecules cm-2 s-1 was recorded at the savannah site. After watering a net emission of N2O was observed. The forest soil produced significantly less N2O compared with the rainy season. As in the rainy season the addition of NH4Cl did not affect the fluxes. Larger emissions were recorded after the application of nitrate. However, the increase was lower than the enhancement produced during the rainy season. The comparison between both seasons indicates that the N2O fluxes strongly depend on the rain pattern of the region, and that during the dry season the bacterial activity or bacterial population responsible for the production of N2O must be low. At present we do not know the mechanism by which dry savannah soil consumes atmospheric N2O. This potential sink is of the same order as the production of N2O due to savannah vegetation burning.