ALBERT

Description: We examined the effects of Asian monsoon rainfall on CH 4 absorption of water-unsaturated forest soil. We conducted a 1-year continuous measurement of soil CH 4 and CO 2 fluxes with automated chamber systems in three plots with different soil characteristics and water content to investigate how temporal variations in CH 4 fluxes vary with the soil environment. CH 4 absorption was reduced by the ‘Baiu’ summer rainfall event and peaked during the subsequent hot, dry period. Although CH 4 absorption and CO 2 emission typically increased as soil temperature increased, the temperature dependence of CH 4 varied more than that of CO 2 , possibly due to the changing balance of activities between methanotrophs and methanogens occurring over a wide temperature range, which was strongly affected by soil water content. In short time intervals (30 min), the responses of CH 4 and CO 2 fluxes to rainfall were different for each plot. In a dry soil plot with a thick humus layer, both fluxes decreased abruptly at the peak of rainfall intensity. After rainfall, CO 2 emission increased quickly, while CH 4 absorption increased gradually. Release of accumulated CO 2 underground and restriction and recovery of CH 4 and CO 2 exchange between soil and air determined flux responses to rainfall. In a wet soil plot and a dry soil plot with a thinner humus layer, abrupt decreases in CH 4 fluxes were not observed. Consequently, the Asian monsoon rainfall strongly influenced temporal variations in CH 4 fluxes, and the differences in flux responses to environmental factors among plots caused large variability in annual budgets of CH 4 fluxes.