In organic soils the availability of electron acceptors determines the ratio of CO₂ to CH₄ formation under anoxic conditions. While typically only inorganic electron acceptors are considered, the importance of electron accepting capacities of organic matter is increasingly acknowledged. Redox properties of organic matter are yet only investigated for a limited set of peat and reference materials. Therefore, we incubated 60 peat samples of 15 sites located in five major peatland regions covering a variety of both bog and fen samples and characterized their capacities to serve as electron acceptor for anaerobic CO₂ production.

We quantified CO₂ and CH₄ formation, and changes in available EAC in anoxic incubations of 56 days. On the time scale of 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 electron acceptor would be needed, we could on average explain 70.8 % by corresponding consumption of EAC from both organic and inorganic electron acceptors, the latter contributing typically less than 0.1 %. When the initial EAC was high, CO₂ formation from apparent consumption of EAC was high and outweighed CO₂ formation from methanogenesis. A rapid depletion of available EAC 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 CH₄ formation in peat soils. Moreover, electron budgets including EAC of organic matter could largely explain anaerobic CO₂ production.