Tree species affect atmospheric CH 4 oxidation without altering community composition of soil methanotrophs

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Plant species exert strong effects on ecosystem functions and one of the emerging, and difficult to test hypotheses, is that plants alter soil functions through changing the community structure of soil microorganisms. We tested the hypothesis for atmospheric CH 4 oxidation by using soil samples from a Siberian afforestation experiment and exposing them to 13C–CH 4. We determined the activity of the soil methanotrophs under different tree species at three levels of initial CH 4 concentration (30, 200 and 1000 ppm) thus distinguishing the activities of low- and high-affinity methanotrophs. Half of the samples were incubated with 13C-enriched CH 4 (99.9%) and half with 12C–CH 4. This allowed an estimation of the amount of 13C incorporated into individual PLFAs and determination of PLFAs of methanotrophs involved in CH 4 oxidation at the different CH 4 concentrations. Tree species strongly altered the activity of atmospheric CH 4 oxidation without appearing to change the composition of high-affinity methanotrophs as evidenced by PLFA 13C labeling. The low diversity of atmospheric CH 4 oxidizers, presumably belonging to the UCSα group, may explain the lack of tree species effects on the composition of soil methanotrophs. We submit that the observed tree species effects on atmospheric CH 4 oxidation indicate an effect on biomass or cell-specific activities rather than by a community change and this may be related to the impact of the tree species on soil N cycling.