Rachel M. Wilson, Jared Ellenbogen, Shuai Yang, Zhen Li, Simon J. McIlroy, Alex B. Cory, Samantha Bosman, A. L. Perry, Cheristy P. Jones, Bridget B. McGivern, Emily K. Bechtold, Yueh-Fen Li, Suzanne B. Hodgkins, McKenzie A. Kuhn, Lyreshka Castro Morales, Kitty Becker, Kenneth H. Williams, Curtis Beutler, Virginia I. Rich, Samuel T. N. Aroney, Ben J. Woodcroft, Scott Saleska, Gene Tyson, Jinyun Tang, Kelly Wrighton, Jeff P. Chanton, R. K. Varner
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.