Electron Accepting Capacities of a Wide Variety of Peat Materials From Around the Globe Similarly Explain CO2 and CH4 Formation.

In organic soils, the availability of terminal electron acceptors (TEAs) determines the ratio of CO₂ to CH₄ formation under anoxic conditions. While the importance of electron accepting capacities (EACs) of organic matter is increasingly acknowledged, redox properties of organic matter have only been investigated in a limited set of peat and reference materials. Therefore, we incubated 60 peat samples from 15 sites covering a variety of both bog and poor to intermediate fen samples and characterized their capacities to serve as TEA for anaerobic CO₂ formation. We quantified CO₂ and CH₄ formation and changes in available EAC in anoxic incubations of 56 days. In our experiment, on average 36.5% of CO₂ could be attributed to CH₄ formation, assuming an CO₂:CH₄ ratio for methanogenesis of 1:1. Regarding the remaining CO₂ formed, for which a corresponding TEA would be needed, we could on average explain 70.8% by corresponding consumption of EAC from both organic and inorganic TEAs, the latter contributing less than 0.1%. When the initial EAC was high, CO₂ formation from the apparent consumption of EAC was high and outweighed CO₂ formation from methanogenesis. Rapid depletion of available EAC, especially in reactive peat, resulted in a higher share of CO₂ from CH₄ formation. Our study demonstrates that EAC provides the most important redox buffer for competitive suppression of methanogenesis in peat soils, particularly under fluctuating water table levels, when EAC is repeatedly regenerated. Moreover, electron budgets including EAC of organic matter could largely explain anaerobic CO₂ production. [ABSTRACT FROM AUTHOR]