Methanotrophic potential of a northern fen

Abstract

Northern peatlands store large quantities of organic carbon that are vulnerable to decomposition under climate warming, producing the greenhouse gases methane (CH 4 ) and carbon dioxide (CO 2 ). Because CH 4 has greater radiative forcing than CO 2 , processes regulating CH 4 emissions strongly influence climate feedbacks. In peatlands, CH 4 oxidation is often assumed to be limited because of the low availability of terminal electron acceptors. Here, we combined peat incubations with field-constrained modeling of CH 4 and CO 2 concentrations and stable isotope profiles to quantify CH 4 cycling in an inundated fen. Potential CH 4 oxidation rates approached 50% of CH 4 production rates, despite persistently waterlogged conditions in the fen. Multi-omic analyses (16S rRNA gene, metagenomic, and metatranscriptomic) showed that the methanotroph community was dominated by aerobic Methylobacter_C taxa with genomic potential for alternative electron acceptor use. In particular Methylobacter_C were actively expressing nirB and narG consistent with respiration of nitrogen compounds. In contrast, anaerobic methane-oxidizing Methanoperedenaceae ANME were detected only at the deepest depth and at very low abundance (0.026%). CH 4 oxidation potential also remained high with depth, contrary to predictions from current ecosystem models, suggesting that deep peat and microaerophilic CH 4 oxidation may be underrepresented in peatland CH 4 budgets.