Chapter 19 Seasonal Variations in CH4 Uptake and CO2 Emission by a Japanese Temperate Deciduous Forest Soil

Abstract

Abstract We measured seasonal variations in soil CH 4 uptake and CO 2 emission for three consecutive years in a cool-temperate, deciduous forest in Japan. The fluxes were measured by the static closed-chamber technique during the growing season and by the gas concentration-gradient technique during winter under snow cover. The measured rates of CH 4 uptake and CO 2 emission showed marked seasonal variations that were correlated with soil temperatures rather than with volumetric soil water content. The Q 10 (10–20°C) value of the CH 4 uptake rates was 1.7, which is higher than that of other temperate forests, and that of the CO 2 emission rates was 3.4 and 4.4 for soil temperatures at 0 and 5 cm depths, respectively. No significant relationship was found between soil moisture and rates of CH 4 uptake or CO 2 emission because of the narrow range of the measured soil water content (15–31% v/v). From June 2002 to May 2003, the estimated annual CH 4 uptake and CO 2 emission were 1.53 and 451 g C y –1 , respectively. When compared with CH 4 uptake rates of temperate deciduous forests worldwide ( n =17), CH 4 uptake rates by Japanese deciduous forest soils are at the high end of the range of reported values. This Japanese temperate forest soil is a strong CH 4 sink. CH 4 oxidation by methanotrophs accounted for 0.4% of the annual soil CO 2 emission. The fluxes through the snowpack composed 14% of the annual CH 4 uptake and 11% of the annual CO 2 emission.