Ishizuka,S., Sakata,T., Sawata,S., Ikeda,S., Sakai,H., Takenaka,C., Tamai,N., Onodera,S., Shimizu,T., Kan-na,K., Tanaka,N. and Takahashi,M.(2009): Methane uptake rates in Japanese forest soils depend on the oxidation ability of topsoil, with a new estimate for global methane uptake in temperate forest. Biogeochemistry, 92, 281-295.


 To clarify the reason for the higher CH4 uptake rate in Japanese forest soils, twenty-seven sites were established for CH4 flux measurement. The first order rate constant for CH4 uptake was also determined using soil core incubation at 14 sites. The CH4 uptake rate had a seasonal fluctuation, high in summer and low in water, and the rate correlated with soil temperature at 17 sites. The annual CH4 uptake rates ranged from 2.7 to 24.8 kg CH4 ha-1 y-1, depending on method of calculation), which is somewhat higher than the uptake rates reported in previous literature. The averaged CH4 uptake take correlated closely with the CH4 oxidation rate of the topsoil (0-5 cm) in the study sites. The CH4 oxidation constant of the topsoil was explained by a multiple regression model using total pore volume of the soil, nitrate content, and C/N ratio (p<0.05, R2 = 0.684). This result and comparison with literature data suggest that the high CH4 uptake rate in Japanese forest soils depends on the high porosity probably due to volcanic ash parent materials. According to our review of the literature, the CH4 uptake rate in temperate forests in Europe is significantly different from that in Asia and North America. A new global CH4 uptake rate in temperate forests was estimated to be 5.4 Tg y-1 (1 SE is 1.1 Tg y-1) on a continental basis.

Keywords: Forest soil; Global methane uptake; Greenhouse gas; Temperate forest』

Materials and methods
 Site description
 Flux measurement
 Soil sampling and analysis
 Soil core analysis
 Statistical analysis
 Seasonal fluctuation of CH4 flux at each site
 Intact soil core incubation analysis
 Variation in CH4 flux among the sites and its relationship with soil properties
 Factors affecting fluctuation of the methane uptake rate in each forest
 Factors affecting the differences in CH4 uptake rates among the sites
 Comparison of CH4 uptake rate with other reports