Effects of snow cover on CO 2 production and microbial composition in a thin topsoil layer

Temperate rain forest soils (>8000 mm yr -1 ) of south of Chile in the East Andes range areintensively affected by increasing freezing and thawing cycles (FTC) due to increasingclimate variability in the last 20 years. Most of these volcanic forests soils are unpolluted(pristine) and receive seasonal snow-cover. In spite of pollutant free precipitations, thesnow cover in these ecosystems contains aerosols, nutrients and microorganisms fromcircumpolar south west winds. These inputs and FTC generate specific conditions at theshallow layer at the soil surface for soil microbiology and biochemistry. The objectives ofthe study were to compare (micro)biological and chemical properties of topsoil and snowcover in an pristine forest and after clear-cut. The organic matter mineralization wasmonitored in a microcosm experiment to explore the effects of FTC and snow melting onredox potential and other topsoil parameters. FTC for soil+snow released more CO 2 inclosed forest (81.9 mg CO 2 kg -1 ) than that after clear-cut (20.5 mg CO 2 kg -1 ). Soil textureand soil organic matter accumulation played a crucial role for organic matter mineralizationand CO 2 fluxes. Gradually increase of temperature after freezing reveled that loamy soilswith certain amount of available C maintain active microbial population that response veryfast to temperature change. Sandy soils with very low C content showed the oppositeresults – very slow response of microbial community and CO 2 fluxes. In conclusion,microbial community structure and functions have distinct transition from snow to the soilin temperate snow-covered forest ecosystem. FTC showed that different microbial groupsare responsible for organic matter mineralization in soil under forest and clear-cut, becausethe pH and redox potential are influenced by snow melting.