Resumen

SANHUEZA, Eugenio. Methane soil-vegetation-atmosphere fluxes in tropical ecosystems. INCI [online]. 2007, vol.32, n.1, pp.30-34. ISSN 0378-1844.

Recently, a surprising discovery indicated that, by an unknown process, vegetation emits methane to the atmosphere. This finding could have serious implications in atmospheric chemistry, climate, and mitigation of global change. In order to evaluate the magnitude of the tropical vegetation source, a re-evaluation of results obtained at various Venezuelan ecosystems is made. CH₄ fluxes from the soil-grass system in savanna ecosystems indicate that grasses produce CH₄ at ~10ng·m^-2·s^-1. Furthermore, CH₄ accumulation within the nocturnal mixing layer at the Guri site, which is affected by savanna and forest emissions, was used to make a rough upper limit estimation of <70ng·m^-2·s^-1 for CH₄ emission from forest vegetation. These estimates are likely to be somewhat low as they do not take into account the light-induced production of CH₄ by the vegetation. Global extrapolation of these fluxes indicates that, ignoring the possible stimulating effects of solar radiation, savanna and forest vegetation result in CH₄ emissions of ~5Tg·yr^-1 and <22Tg·yr^-1, respectively. These estimates are in agreement with the lower estimates based on laboratory CH₄ flux measurements, reported in the literature. On the other hand, the global extrapolation of the atmosphere-soil uptake fluxes results CH₄ sinks of ~1.3Tg·yr^-1 in savannas and of 3.3Tg·yr^-1 in forests. In conclusion, Venezuelan field measurements support the discovery that vegetation emits CH₄. However, global extrapolation indicates that tropical vegetation would contribute modestly to global methane emission, which, additionally, is offset in part by savanna and forest CH₄ soil uptake. Most likely, carbon sequestration benefits from forestation should not be significantly affected by CH₄ emissions by trees.

Palabras clave : Global Methane Budget ; Methane from Vegetation ; Methane in Tropical Ecosystems.