Effects of Snow Cover on Carbon Dioxide Emissions and Their & delta;C-13 Values of Temperate Forest Soils with and without Litter

The presence of litter and winter snow cover can affect the decomposition of organic matter in forest soils and changes in d(13)C values of soil-respired carbon dioxide (CO2). However, limited information is available on the responses of CO2 emissions from forest soils and their d(13)C values to snow cover and litter addition over the year. We experimentally manipulated snow cover to study the impacts of light and heavy artificial snow cover on soil heterotrophic respiration and its d(13)C values, using undisturbed large soil columns collected from two typical temperate forests in Northeastern China. Based on the average temperatures of surface forest soils in four seasons of the year in this study region, the simulations of autumn freeze-thaw, winter freeze, spring freeze-thaw, and the growing season were sequentially carried out under laboratory conditions. A set of novel analysis systems, including automated chamber equipment and laser spectroscopy analysis with high-frequency measurements for CO2 concentrations and the C-13/C-12 isotopic ratios in CO2, was used to study the effects of artificial snow cover and the presence of litter on soil heterotrophic respiration and its d(13)C values. During the autumn freeze-thaw simulation, there were larger CO2 emissions and less negative d(13)C values of soil-respired CO2 upon heavy snow cover than upon light snow cover, indicating that the presence of increased snow cover prior to winter freeze can increase the decomposition of organic C in subsurface soils under temperate forests. The d(13)C values of soil-respired CO2 in all treatments were, on average, less negative as the simulated spring freeze-thaw proceeded, which was contrary to the variations of the d(13)C during the autumn freeze-thaw simulation. Soil heterotrophic respiration and its d(13)C values during the spring freeze-thaw simulation were, on average smaller upon heavy snow cover than upon light snow cover, which differed from those during the autumn freeze-thaw and growing season simulations, respectively. Taken together, the results highlight that the effects of snow cover on soil heterotrophic respiration and its d(13)C values under temperate forests may vary with different seasons of the year and the presence of litter.