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Summary

Methanotrophic bacteria in soils derived from volcanic ash (Andisols) were characterized via time series 13C-phospholipid fatty acid (PLFA) labelling. Three Andisols were incubated under 2 ppmv 13CH4 for up to 18 weeks, thus enabling high-affinity methanotrophs to be selectively characterized and quantified. PLFA profiles from all soils were broadly similar, but the magnitude of the high-affinity methanotrophic populations determined through 13C-PLFA-stable isotope probing displayed sizeable differences. Substantial incorporation of 13C indicated very large high-affinity methanotrophic populations in two of the soils. Such high values are far in excess (10×) of those observed for a range of mineral soils incubated under similar conditions (Bull et al., 2000; Maxfield et al., 2006; 2008a, b). Two of the three Andisols studied also displayed high but variable CH4 oxidation rates ranging from 0.03 to 1.58 nmol CH4 g−1 d.wt. h−1. These findings suggest that Andisols, a previously unstudied soil class with respect to high-affinity methanotrophic bacteria, may oxidize significant amounts of atmospheric methane despite their low areal coverage globally.