The release of CO2 from the snow surface in winter and the soil surface in summer was directly or indirectly measured in four cool-temperate deciduous broadleaved and evergreen needle forests. The closed chamber method (CC-method) and Fick's diffusion model (DM-method) were used for the direct and indirect measurements, respectively. The winter soil temperatures from the soil surface to 10 cm depth were between 0 and 2°C. The concentration of CO2 within snowpack increased linearly with increasing snow depth. The average effluxes of CO2 calculated from the gradients of CO2 concentration in the snow using the DM-method ranged from 20 to 75 mg CO2 m-2 h-1, while the CC-method showed the average effluxes of 20 to 50 mg CO2m-2h-1. These results reveal that the snow thermally insulates the soil, allowing CO2 production to continue at soil temperatures a little above freezing throughout the winter. Carbon dioxide formed in the soil can move across snowpack up to the atmosphere. The winter/summer ratio of CO2 emission was estimated to be higher than 7%. Therefore, the snow-covered soil served as a source of CO2 in the winter and the effluxes represent an important part of the annual CO2 budget in snowy regions.
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