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

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