Influences of snow cover and soil-frost on ground surface flux and soil gas concentration of CO2 in an agricultural land in northern Japan

Our main objective was to elucidate how snow cover and soil frost influenced CO2 dynamics over agricultural land. We observed the CO2 flux above the soil or snow surface continuously using the commonly used static-chamber method and the CO2 concentration 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 CO2 flux was 3.9 μmol m-2 s-1 and CO2 concentration in soil was 390-5000 ppm. Little CO2 flux was observed during the soil-freezing and snow-covered periods. The CO2 concentration had been increasing about 10 ppm day-1 during the soil-freezing period at the snow-removal plot. At the beginning of April, the CO2 flux increased temporarily up to 0.19 μmol m-2 s-1 after the snow melted entirely at the untreated control plot and up to 0.52 μmol m-2 s-1 after the soil had thawed at the snow-removal plot. Snow-melting and soil-thawing largely influenced on CO2 flux, irrespective of soil temperature. The data were not explained by conventionally used temperature response functions for CO2 fluxes in these periods.