EMISSIONS OF NITROGEN-OXIDES FROM EQUATORIAL RAIN-FOREST IN CENTRAL-AFRICA - ORIGIN AND REGULATION OF NO EMISSION FROM SOILS

Emissions of nitric oxide from soils of equatorial rain forest were me asured in the Dimonika Natural Park (4-degrees30'S, 12-degrees30'E) in the Mayombe Forest in Congo. Three research campaigns were carried ou t in June and July 1991 and in February 1992. Fluxes were measured by dynamic chamber techniques using a chemiluminescence instrument Scintr ex LMA3. NO fluxes measured on natural soils are in between 5 and 17 x 10(9) molecules cm-2 s-1; they are of the same order of magnitude as those observed in similar tropical forest media. Soil treatment experi ments show that the auto-decomposition of HNO2 in these acid soils (pH # 4) (chemodenitrification) is a potentially important cause of nitri c oxide production in this type of ecosystem. Nitrous acid comes from autotrophic nitrification all the year round, and also from biological denitrification, shown by N2O emissions, during the rainy season. The regulation of NO release from soils is linked to ammonia production f rom litter mineralisation and to direct NH4 input by throughfall.