Methane Oxidation Potential of Arctic Wetland Soil of Taiga-Tundra Ecotone in Northeastern Siberia
1Grad. Sch. Bioagr. Sci., Nagoya Univ., 2Fac. Earth Environ. Sci., Hokkaido Univ., 3Grad. Sch. Environ. Sci., Hokkaido Univ., 4Inst. for Biol. Problems of Cryolithozone
Arctic wetlands are significant sources of atmospheric methane and the observed accelerated warming of the arctic causes increased methane formation in water-saturated tundra soil with deepened permafrost thawing. Methane oxidation is regarded as the key process to regulate methane emission from wetlands. In this study we determined the potential methane oxidation rate of the wetland soils of a Taiga-Tundra transition zone in Northeastern Siberia. Peat soil samples were collected in the summer from depressions that were covered with tussocks of sedges and Sphagnum spp. and from mounds vegetated with moss and larch trees. The potential methane oxidation rate was estimated by a bottle incubation experiment in which homogenized soil samples were incubated with methane at the initial concentration of 0.5-0.8 %v/v. Soil samples from the mounds showed no detectable methane oxidation, whilst the soils collected from depressions exhibited active methane oxidation with no lag. The potential methane oxidation rates at 15 _C were of 270 and 190 nmol h-1 g-1 dw in the moss- and sedge-dominated zones, respectively. Methane oxidation was active over the depths including the water-saturated anoxic layers. The maximum methane oxidation rate was recorded in the layer above the water-saturated layer: the surface (0-2cm) layer in the sedge-dominated zone and in the middle (4-6 cm) layer in the moss-dominated zone. Temperature-dependent methane oxidation was observed at the range of temperature from 0 to 15 _C. The estimated threshold temperature of methane oxidation was -4 to -11 _C, which suggested methane oxidation at subzero temperatures. The frozen layer of Sphagnum peat also showed immediate methane consumption when incubated at 15 _C. The present results suggest that methane oxidizing bacteria keep their activity in the wetland soils even under anoxic and frozen conditions and immediately utilize methane when the conditions become favorable.
keywords:Anoxia,Methane oxidation,Permafrost,Psychrotolerance,Sphagnum peat,