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.

Soil respiration (Rs) plays a key role in the carbon balance of forest ecosystems. There is growing evidence that Rs is strongly correlated with canopy photosynthesis; however, how Rs is linked to aboveground attributes at various phenological stages, on the seasonal and diurnal scale, remains unclear. Using an automated closed dynamic chamber system, we assessed the seasonal and diurnal patterns of Rs in a temperate evergreen coniferous forest from 2005 to 2010. High-frequency Rs rates followed seasonal soil temperature patterns but the relationship showed strong hysteresis. Predictions of Rs based on a temperature-response model underestimated the observed values from June to July and overestimated those from August to September and from January to April. The observed Rs was higher in early summer than in late summer and autumn despite similar soil temperatures. At a diurnal scale, the Rs pattern showed a hysteresis loop with the soil temperature trend during the seasons of high biological activity (June to October). In July and August, Rs declined after the morning peak from 0800 to 1400 h, although soil temperatures continued to increase. During that period, figure-eight-shaped diurnal Rs patterns were observed, suggesting that a midday decline in root physiological activity may have occurred in early summer. In September and October, Rs was higher in the morning than in the night despite consistently high soil temperatures. We have characterised the magnitude and pattern of seasonal and diurnal Rs in an evergreen forest. We conclude that the temporal variability of Rs at high resolution is more related to seasons across the temperature dependence.

Very few studies have conducted long-term observations of methane (CH 4 ) flux over forest canopies. In this study, we continuously measured CH 4 fluxes over an evergreen coniferous (Japanese cypress) forest canopy throughout 1 year, using a micrometeorological relaxed eddy accumulation (REA) system with tuneable diode laser spectroscopy (TDLS) detection. The Japanese cypress forest, which is a common forest type in warm-temperate Asian monsoon regions with a wet summer, switched seasonally between a sink and source of CH 4 probably because of competition by methanogens and methanotrophs, which are both influenced by soil conditions (e.g., soil temperature and soil moisture). At hourly to daily timescales, the CH 4 fluxes were sensitive to rainfall, probably because CH 4 emission increased and/or absorption decreased during and after rainfall. The observed canopy-scale fluxes showed complex behaviours beyond those expected from previous plot-scale measurements and the CH 4 fluxes changed from sink to source and vice versa.

Continuous in situ measurements of methane (CH 4) fluxes from intact leaves and trunk of Japanese cypress (Chamaecyparis obtusa Sieb. et Zucc) were conducted in a temperate forest from August 2009 to August 2010. An automated closed chamber system, which was used to evaluate CO 2 exchange between the atmosphere and forest ecosystems, was coupled to a laser-based instrument to monitor CH 4 concentrations. Temporal changes in CH 4 concentrations from the foliage and trunk were measured at one-second intervals during chamber closure to determine CH 4 fluxes between the leaf and trunk surfaces and the atmosphere. While recent studies have suggested that some plants emit CH 4 under aerobic conditions, emission or uptake of CH 4 in detectable amounts with our experimental system, by intact leaves or the trunk of C. obtusa, was not significantly observed throughout the measurement period.