Afforested sites in a temperate grassland region: influence on soil properties and methane uptake

Methane (CH4) flux at the soil-atmosphere interface (SAI) results from the balance between CH4 production (methanogenesis) and CH4 consumption (methanotrophy). The latter predominates in well-aerated mineral soils; is affected by a combination of abiotic and biotic factors, especially soil diffusivity, which depends on soil properties, and methanotroph activity. This work reports results of CH4 fluxes from afforested sites located in a temperate region of formerly native grassland in Buenos Aires Province (Argentina, Southern Hemisphere), taking a naturalized pasture as a reference. Methane concentration [CH4] and soil parameters along the soil profile were also measured to understand intersite differences in CH4 fluxes at the SAI, that could be related to vegetation cover and its influence on soil properties and therefore, on CH4 soil diffusivity. At all sites soils were CH4 sinks in the range of -3.55 to -14.39 ng CH4 m(-2) s(-1); the naturalized pasture presented the weakest one. Intersite differences in CH4 fluxes may result from differences observed in [CH4] profiles and CH4 diffusion coefficients. [CH4] variation could be explained mainly by differences in silt and clay content and bulk density that affect CH4 soil diffusivity. These could be the result of afforestation that seems to improve the physical and biological soil attributes linked to CH4 consumption as it meliorates its diffusivity.