Atmospheric methane consumption in adjacent arable and forest soil systems

During a 24 h incubation at 15°C atmospheric methane uptake was measured in closed bottles containing moistened (30% v/v) structurally different soils from five sites in southern Norway. Each site had a natural sub-site and an adjacent disturbed counterpart within 50 m. Highest methane uptake was found in the uppermost mineral horizon in undisturbed forest soils, with a maximum of 1.154±0.002 ng CH4 g−1 dw soil h−1. In contrast, the adjacent disturbed arable counterpart of this site had a 130-fold reduction in CH4 uptake (9±3 pg CH4 g−1 dw h−1). The highest uptake rate in arable soils was 129±8 pg CH4 g−1 dw h−1. This site was a former forest soil, cultivated for only 2 years. Similar CH4 uptake rates occurred at a forested spruce site which had earlier been cultivated. In 1994, 30 years after forestation, this soil had a subsurface methane uptake of 134±8 pg g−1 dw h−1, the lowest uptake found for top mineral forest soil. Conditioning the fresh soil samples at 15°C for 3 weeks in a 20% CH4 atmosphere changed the soilʹs capacity to consume atmospheric methane. Generally the methane uptake rates at ambient CH4 concentrations increased in arable soils whereas the uptake rates decreased in forest soils. Blocking methane oxidation with dimethyl ether resulted in a considerable methane accumulation. Methane production was highest in the top organic soil horizons, with a maximum of 7.31 ng CH4 g−1 dry soil 24 h−1.