Terminal mineralization of organic carbon (C) in northern peat soils usually produces more carbon dioxide (CO2) than methane (CH4), but the maintenance of microbial CO2 production is unclear. Carbon dioxide production relies on oxygen (O2) or alternative (to O2) electron acceptors (NO 3 − , Fe(III), SO 4 2− ). We examined rates of CO2 production and CH4 production in peat soils from two ombrotrophic bogs and two minerotrophic fens incubated in vitro with and without added glucose (an electron donor) and added electron acceptors. Soil interstitial water had dissolved NO 3 − (2–17 μmol L−1) in three sites, and SO 4 2− (2–20 μmol L−1) and Fe(III) (0.02–0.8 μmol L−1) in all four sites. Peat soils incubated in vitro without added glucose or electron acceptors had rates of CH4 production between 0.2 and 1.5 μmol g−1 day−1 and rates of CO2 production between 8 and 17 μmol g−1 day−1. Added glucose increased CO2 production in all of the peat soils, although adding an electron acceptor with glucose had no additional impact in the bogs. Nitrate plus glucose had the largest increase in CO2 production in both fens, and SO 4 2− plus glucose enhanced CO2 production in one fen. Added glucose alone or with O2 or Fe increased CH4 production in peat soil from the two bogs, whereas glucose plus SO 4 2− or NO 3 − inhibited CH4 production. Glucose plus an electron acceptor inhibited CH4 production in the forest fen but enhanced CH4 production in sedge fen. Terminal electron acceptors did not universally divert C and electron flow away from CH4 production and towards CO2 production in these peat soils, and thus maintenance of CO2 production is still uncertain, with no single explanation likely.
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