Soil emissions of nitrous oxide from savannahs in Africa: estimating annual rates

摘要

African savannah ecosystems account for two-thirds of the savannahs worldwide, but there are only few estimates of soil emissions of nitrous oxide (N_2O). In order to study temporal and spatial variation of emission rates, measurements of N_2O fluxes were conducted in seasonal dry savannahs in Ethiopia and Ghana. Soil emissions were measured by an enclosure technique at natural vegetation and fallow sites. The mean soil emission rate was 0.5 μg N_2O-N m~(-2) h~(-1) in the dry season and increased during the rainy season from 1.7 to 5.5 μg N_2O-N m~(-2) h~(-1). A nutrient addition experiment showed that nitrification and denitrification processes have potentials to contribute to N_2O production. The global soil emission of N_2O from tropical savannahs was estimated at 0.52 Tg N_2O-N yr~(-1) by extrapolating data from the present study and data from Venezuela published by others. The suggested annual rate presented here amounts to two-thirds of the figure from a modeling study.