Methane oxidation potential of the arctic wetland soils of a taiga-tundra ecotone in northeastern Siberia

Arctic wetlands are significant sources of atmospheric methane and the observed accelerated climate changes in the arctic could cause a change in methane dynamics. Methane oxidation would be the key process to control 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 summer from depressions covered with tussocks of sedges and Sphagnum spp. and from mounds vegetated with moss and larch trees. An aerobic bottle incubation experiment demonstrated that the soil samples collected from depressions in the moss- and sedge-dominated zones exhibited active methane oxidation with no time lag, while the mound soils showed no methane oxidation under the given conditions. The potential methane oxidation rates of the soils at 15°C ranged from 94 to 496 nmol h⁻¹ g⁻¹ dw. The immediate and active methane oxidation was observed over the depths studied (0–40 cm) including the water-saturated anoxic layers; the maximum methane oxidation rate was recorded in the layer above the water-saturated layer. The methane oxidation rate was temperature-dependent, but substantial methane oxidation was observed even at 0°C particularly for the moss soil samples. Soil samples collected from the frozen layer of Sphagnum peat also showed immediate methane consumption when incubated at 15°C. The present results suggest that the methane oxidizing bacteria in the wetland soils could survive under anoxic and frozen conditions keeping their potential activities and immediately utilize methane when the conditions become favorable. On the other hand, the inhibitor of methane oxidation (difluoromethane) did not affect the methane flux from the sedge and moss zones in situ, which suggested the minor role of plant-associated methane oxidation.