BayCEER Workshop 2008

Atmospheric methane uptake in different forest soils is driven by similar methanotrophic communities.

Deciduous forest soils exhibit higher atmospheric methane uptake rates than coniferous ones. Analogous to the differences in vegetation, it is conceivable that different methanotrophic communities may be present. In spring 2006 soil samples were collected from a spruce- and beech-dominated forest site. Both sites were adjacent and the soil type was identical (Haplic Luvisol, Höglwald, Germany). At a methane concentration of 1.8 ppmv potential oxidation rates were measured. Soil samples from the beech-dominated site exhibited a four times higher atmospheric methane oxidation potential. The highest activity was detected in layers below the humus. This indicates a possible inhibition of methane oxidation in the humus layer. The phylogenetic affiliation of methanotrophs involved in the uptake of atmospheric methane was assessed by analysing the pmoA gene. It encodes for the hydroxylase of the particulate methane-monooxygenase. Methanotrophic genotypes were identified separately at both sites and different depths by pmoA-targeting T-RFLP (terminal restriction fragment length polymorphism) analysis. The resulting T-RFs (terminal restriction fragments) were assigned to pmoA clone sequences from the same sites. USCa and a novel pmoA genotype (Cluster 6) were detected. No differences in identified T-RFs occurred with increasing depth or between the samples of the two sites. The results suggest that both clusters dominate the community of methanotrophs in soils of the both sites independently on the dominating tree species. Thus, different atmospheric methane uptake rates are not likely caused by differences in the methanotrophic community structure. Other causes, for example differences in the total abundance of methanotrophic bacteria, are conceivable.