Activity and structure of methanotrophic communities in landfill cover soils

The composition of the methanotrophic community in soil covers on five landfills in Northern and Eastern Germany was investigated by means of diagnostic microarray and terminal restriction fragment length polymorphism (T-RFLP), both targeting the pmoA gene of methanotrophs. Physical and chemical properties of the 15 sampled soil profiles varied greatly, thus providing for very different environmental conditions. The potential methane oxidation activity, assessed using undisturbed soil cores, varied between 0.2 and 28 μg CH 4 g dw -1 h -1, the latter amounting to 426 g CH 4 m -2 h -1. Total nitrogen was found to be the soil variable correlating most strongly with methanotrophic activity. Explaining close to 50% of the observed variability, this indicates that on the investigated sites activity and thus abundance of methanotrophs may have been nitrogen-limited. Variables that enhance organic matter and thus nitrogen accumulation, such as field capacity, also positively impacted methanotrophic activity. In spite of the great variability of soil properties and different geographic landfill location, both microarray and T-RFLP analysis suggested that the composition of the methanotrophic community on all five sites, in all profiles and across all depths was similar. Methylocystis, Methylobacter and Methylococcus species, including Methylococcus-related uncultivated methanotrophs, were predominantly detected among type II, Ia and Ib methanotrophs, respectively. This indicates that the high methane fluxes typical for landfill environments may be the most influential driver governing the community composition, or other variables not analysed in this study. Principal component analysis suggested that community diversity is most influenced by the site from which the samples were taken and second, from the location on the individual sites, i.e. the soil profile. Landfill and individual profiles reflect the combined impact of all effective variables, including those that were not measured in this study.