EMISSION OF NITRIC-OXIDE FROM SOILS AND TERMITE NESTS IN A TRACHYPOGON SAVANNA OF THE ORINOCO BASIN

Nitric oxide fluxes from soils in the Trachypogon savanna of the Orino co basin were deter mined during the dry season using the static chamb er method. The emission from dry soils fluctuated from 0.4 to 3 ng N m (-2) s(-1) and increased up to 25 ng N m(-2) s(-1) after moderate wate ring or light rainfalls (1 to 5 mm). The mean emission values are up t o 6 times lower than one observed earlier at the Chaguaramas site, but up to 10 times higher than one recorded at the Guri site, indicating an important spatial variability in NO fluxes of the Venezuelan savann a region. The changes observed after the addition of nitrogen to the s oil, in the form of ammonium and/or nitrate, indicate a high denitrifi cation potential in this acidic soil. Burning of the surface vegetatio n produced an increase by a factor of 10 in the emission rate of NO, b ut the effect was relatively short in time, about 5 days. It was estim ated for the savanna region that burning increases the total NO soil e mission during the dry season by 15% compared to the unburnt case. Soi ls with termite nests emit 10 times more NO than soil without nests, b ut the contribution from this source is less than 2% of the total sava nna soil flux.