Atmospheric methane consumption in adjacent arable and forest soil systems

Abstract

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 CH 4 g −1 dw soil h −1. In contrast, the adjacent disturbed arable counterpart of this site had a 130-fold reduction in CH 4 uptake (9±3 pg CH 4 g −1 dw h −1). The highest uptake rate in arable soils was 129±8 pg CH 4 g −1 dw h −1. This site was a former forest soil, cultivated for only 2 years. Similar CH 4 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% CH 4 atmosphere changed the soil's capacity to consume atmospheric methane. Generally the methane uptake rates at ambient CH 4 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 CH 4 g −1 dry soil 24 h −1.