Seasonal variation of N₂O fluxes at a tropical savannah site: Soil consumption of N₂O during the dry season

Abstract

Soil fluxes of N 2 O 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±2.7×10 9 N 2 O molecules cm −2 s −1 was recorded at the savannah site. After watering a net emission of N 2 O was observed. The forest soil produced signicantly less N 2 O compared with the rainy season. As in the rainy season the addition of NH 4 Cl 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 N 2 O 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 N 2 O must be low. At present we do not know the mechanism by which dry savannah soil consumes atmospheric N 2 O. This potential sink is of the same order as the production of N 2 O due to savannah vegetation burning.