Soil organic matter (SOM) may act as a diffusionbarrier and as a result of this may limit the amount of atmospheric methane that methanotrophic bacteria present in soil can consume. A reduction of the amount of SOM could lead to an increase in methane consumed. The effects of the thickness of soil organic matter on methane flux were studied at the forest-tundra ecotone in the subarctic zone, Abisko. During four weeks in July/August, 2001, methane flux was measured in situ before and after removal of parts of the soil organic matter and samples from soil profiles of both tundra and forest soil were collected and incubated in the laboratory. The incubation showed that by far the highest methane consumption was found in the top one centimeter of the mineral soil from the forest profiles, while the tundra profiles, by contrast, had methane consumption throughout the organic horizon, but not in the mineral layers. The results of removing parts of the organic layers in the field did not yield any statistically significant data, but seemed to indicate an increase in methane consumption at the forest site, possibly due to increased diffusion rates, and a decrease in consumption at the tundra site, possibly because of the removal of parts of the methanotrophic community together with the organic material.
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