The impact of burning and Calluna removal on below-ground methanotroph diversity and activity in a peatland soil

Methanotroph community structure and activity was investigated in a peat soil in which the above-ground vegetation was burned repeatedly during the last 50 years, and in soil unburned since 1954. Regular burning (every 10 years) was found to have no obvious impact on the potential methane-uptake capacity; however, a lower abundance of type I methanotrophs relative to type II methanotrophs in the frequently burned soils was observed using pmoA (encoding a key polypeptide of particulate methane monooxygenase) microarray analyses. Denaturing gradient gel electrophoresis of bacterial 16S rRNA genes indicated that the total bacterial community, and not just the methanotrophs, was affected by the burning. The regular burning also resulted in a decreased abundance of Calluna vegetation relative to mixed grasses in the peatland plots. In a separate mesocosm experiment, Calluna plants and their roots were removed from the peat soils for a growing season (from February 2006 to November 2006). It was shown that removal of Calluna from the soil greatly decreased the methane-uptake capacity of the soils, although no obvious impact on the methanotroph population structure was observed. Real-time PCR quantification of pmoA genes showed that the abundance of methanotrophs in barren soil (without Calluna vegetation) was about fivefold less than in the control soil (with Calluna vegetation). These findings indicate that the methanotroph community is strongly influenced by the above-ground vegetation cover. Burning of Calluna seemed to favour the type II metbanotrophs, whereas the removal of the Calluna cover did not appear to affect the relative abundance of methanotroph genera but caused a uniform decrease in the size of methanotroph populations.