Links between methanotroph community composition and CH4 oxidation in a pine forest soil

The main gap in our knowledge about what determines the rate of CH4 oxidation in forest soils is the biology of the microorganisms involved, the identity of which remains unclear. In this study, we used stable-isotope probing (SIP) following (CH4)-C-13 incorporation into phospholipid fatty acids (PLFAs) and DNA/RNA, and sequencing of methane mono-oxygenase (pmoA) genes, to identify the influence of variation in community composition on CH4 oxidation rates. The rates of C-13 incorporation into PLFAs differed between horizons, with low C-13 incorporation in the organic soil and relatively high C-13 incorporation into the two mineral horizons. The microbial community composition of the methanotrophs incorporating the C-13 label also differed between horizons, and statistical analyses suggested that the methanotroph community composition was a major cause of variation in CH4 oxidation rates. Both PLFA and pmoA-based data indicated that CH4 oxidizers in this soil belong to the uncultivated 'upland soil cluster alpha'. CH4 oxidation potential exhibited the opposite pattern to C-13 incorporation, suggesting that CH4 oxidation potential assays may correlate poorly with in situ oxidation rates. The DNA/RNA-SIP assay was not successful, most likely due to insufficient C-13-incorporation into DNA/RNA. The limitations of the technique are briefly discussed.