ATMOSPHERIC METHANE CONSUMPTION IN ADJACENT ARABLE AND FOREST SOIL SYSTEMS

During a 24 h incubation at 15 degrees C atmospheric methane uptake wa s measured in closed bottles containing moistened (30% v/v) structural ly different soils from five sires in southern Norway. Each site had a natural sub-site and an adjacent disturbed counterpart within 50 m. H ighest methane uptake was found in the uppermost mineral horizon in un disturbed 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 spru ce site which had earlier been cultivated. In 1994, 30 years after for estation, 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. Con ditioning the fresh soil samples at 15 degrees C for 3 weeks in a 20% CH4 atmosphere changed the soil's capacity to consume atmospheric meth ane. 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 c onsiderable methane accumulation. Methane production was highest in th e top organic soil horizons, with a maximum of 7.31 ng CH4 g(-1) dry s oil 24 h(-1). (C) 1998 Elsevier Science Ltd. All rights reserved.