Molecular Soil Biology 2026, Vol.17, No.1, 12-25 http://bioscipublisher.com/index.php/msb 20 6.2 Oxidation-reduction gradient and electron acceptor competition mechanism When explaining "why increasing oxygen reduces methane", the competition among electron acceptors is often regarded as a key factor. In many paddy soil environments, the duration of the iron reduction stage can affect when methane production begins. If the soil is rich in iron, acidic, and has sufficient oxidants, the methane production process may be suppressed for a long time (Fan et al., 2018). On the other hand, the role of electron acceptors is not only to compete with methane production for substrates, but they may also participate in the formation of new methane "consumption pathways". For example, some studies have found that anaerobic methane oxidation (AOM) can occur with the participation of electron acceptors such as trivalent iron or nitrate (Ettwig et al., 2016). Such processes can to some extent reduce methane emissions from paddy fields and also identify active microbial groups related to electron acceptor reduction. If this mechanism is viewed in the context of alternate wetting and drying irrigation, it becomes easier to understand: the fields repeatedly change between drying and re-flooding, and the oxidation-reduction gradient is constantly being re-adjusted. On the one hand, this will inhibit the activity of methane-producing bacteria, while on the other hand, it provides phased opportunities for the iron cycle, nitrogen cycle, and AOM. Eventually, this often manifests as a decrease in net methane flux (Figure 5). Figure 5 Analysis of mechanisms for methane emission reduction in rice paddies
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