Control of organic carbon mineralization by alternative electron acceptors in four peatlands, Central New York State, USA

Abstract

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 ²⁻₄ ). 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 ²⁻₄ (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 ²⁻₄ 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 ²⁻₄ 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.