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4,500,000 yen
To estimate the variety of CH4 uptake rates by the soil in a forest 18 stainless chambers were set for flux measurement. Nine were set on upper part of a slope, and the other nine were set on lower part of the slope. The mean flux of CH4 in 18 chambers was -3.08¡Þ0.72 and -3.20¡Þ0.74 mgCH4m-2d-1 in June and July, respectively. The result indicates that the use of only three chambers in one sampling location is enough to estimate the mean flux in a forest floor, and we recommend to set six chambers (three on upper part of a slope and three on lower part of the slope) for more precise estimation of CH4 flux. A three-year measurement of CH4 flux was conducted in a natural deciduous forest in Ibaraki between Mar. 1995 and Nov. 1997. The mean flux was 4.9 and 2.5 mgCH4m-2d-1 near a ridge and on an upper part of a valley, respectively. The CH4 flux showed a seasonal variation, higher in summer and lower in winter. The inter-annual variation of the CH4 uptake rate between 1995 and 1997 was small at both sites. The mean flux near a ridge was relatively larger than literature values ever given for temperate ecosystems.
The first intensive research on N2O emission in Asian forests has been conducted in a suburb of Tokyo City since 1998. A clear seasonal variation of N2O flux was observed in all of three locations along the slope of a deciduous forest in which the N2O fluxes were correlated well with the soil temperature (r2=0.66-0.82). Throughout a year, the N2O emission at more humid bottom location was twice as much as in other locations. On the basis of these observations, an annual N2O emission rate was calculated as 0.56 kg N ha-1. This value is considerably higher in comparison with literature values ever given for temperate ecosystems, suggesting a crucial importance of 'nitrogen-saturation' as a factor controlling N2O emission from forests in Japan.
nitrous oxide(N2O), methane(CH4), forests, natural soils, Monsoon Asia