Influences of snow cover and soil-frost on ground surface flux and soil gas concentration of CO₂in an agricultural land in northern Japan

Our main objective was to elucidate how snow cover and soil frost influenced CO₂dynamics over agricultural land. We observed the CO₂flux above the soil or snow surface continuously using the commonly used static-chamber method and the CO₂concentration in the soil on snow-removal plot and untreated control plot over agricultural land in northern Japan from September 25, 2009, to May 31, 2010. The recorded largest CO₂flux was 3.9 μmol m^-2 s^-1and CO₂concentration in soil was 390-5000 ppm. Little CO₂flux was observed during the soil-freezing and snow-covered periods. The CO₂concentration had been increasing about 10 ppm day^-1during the soil-freezing period at the snow-removal plot. At the beginning of April, the CO₂flux increased temporarily up to 0.19 μmol m^-2 s^-1after the snow melted entirely at the untreated control plot and up to 0.52 μmol m^-2 s^-1after the soil had thawed at the snow-removal plot. Snow-melting and soil-thawing largely influenced on CO₂flux, irrespective of soil temperature. The data were not explained by conventionally used temperature response functions for CO₂fluxes in these periods.