Unravelling substrate availability and redox interactions on methane production in peat soils of China

Abstract The availability of electron acceptors (EAs) in peatlands determines the potential of methane (CH 4 ) formation under waterlogged conditions. Previous studies suggested that EAs can suppress CH 4 production based on Gibbs free energy under the Redox Ladder Theory. However, growing evidence challenges this theory, raising the question of how the coupling of soil substrates with EAs influences CH 4 emissions. To answer this key question, peat soils were collected across different climatic zones with different degrees of soil degradation. Anoxic incubation experiments were set up, and continuous addition of SO 4 2− , Fe 3+ and humic acid (HA) at different concentrations was followed by characterization of dissolved organic matter using fluorescence spectroscopy. Results suggest that low concentrations of SO 4 2− (1000 μmol L −1 ), Fe 3+ (100 μmol L −1 ) and HA (30 mgC L −1 ) promoted CH 4 production in most of the peat soils. With the addition of SO 4 2− and HA, increased CH 4 emissions were attributed to the facilitation of dissolved organic carbon and increased quinone‐like component C1, which increased the substrate availability for methanogenesis. Furthermore, strengthened microbial activity as indicated by fluorescence component C2 led to higher CH 4 production under Fe 3+ treatments. On the other hand, at high concentrations of SO 4 2− (5000 μmol L −1 ), Fe 3+ (500 μmol L −1 ) and HA (50 mgC L −1 ), CH 4 emissions rapidly decreased by 70.65 ± 1.57% to 96.25 ± 0.45% compared to control group without EAs addition, accompanied by increased δ 13 C‐CH 4 signatures indicating the outweighed CH 4 production under anaerobic oxidation of methane (AOM) when coupling with reduced EAs. The effect of EAs on CH 4 emissions in peat soils could also be related to lability and characteristics of natural organic matter. Our results suggest that the CH 4 production in waterlogged peatlands could be facilitated by regulating organic substrates at low EAs concentrations, but excessive EAs will reduce net CH 4 emissions through AOM. The valuable discovery of CH 4 production and oxidation processes provides insights for mitigating methane emissions from peatlands and regulating global climate change.