Methane oxidation in Japanese forest soils

To evaluate the CH4 uptake rate in Japanese deciduous and coniferous evergreen forest soils, the CH4 flux and CH4 concentration in soil gas were measured at seven sites in central Japan. The CH4 uptake potential was calculated from incubation of soil cores. The CH4 fluxes at all sites were negative (uptake by the soils) at every sampling time. The CH4 uptake rate was very high (7.6 mg CH4 m−2 d−1) in one deciduous forest soil. Fluxes were highly correlated to the air temperature except a coniferous forest site. The most active layer of CH4 uptake in each plot differed with site: subsurface (10–15 cm) at two coniferous forest sites and topsoil (0–5 cm) at the other five sites. The potential of the subsurface layer to oxidize CH4 made a substantial contribution to soil CH4 uptake mechanisms, especially when the topsoil had a low ability to oxidize CH4. Methane uptake rates were nine times higher than those of previous studies. The soil CH4 uptake rate on a global scale may be underestimated.