Soil organic carbon regulates CH production through methanogenic evenness and available phosphorus under different straw managements.

Methane (CH) is the main greenhouse gas emitted from rice paddy fields driven by methanogens, for which methanogenic abundance on CH production has been intensively investigated. However, information is limited about the relationship between methanogenic diversity (e.g., richness and evenness) and CH production. Three independent field experiments with different straw managements including returning method, burial depth, and burial amount were used to identify the effects of methanogenic diversity on CH production, and its regulating factors from soil properties in a rice-wheat cropping system. The results showed that methanogenic evenness (dominance) can explain 23% of variations in CH production potential. CH production potential was positively related to methanogenic evenness (R = 0.310, p < 0.001), which is driven by soil organic carbon (SOC), available phosphorus (AP), and nitrate (NO) through structure equation model (SEM). These findings indicate that methanogenic evenness has a critical role in evaluating the responses of CH production to agricultural practices following changes in soil properties. The SEM also revealed that SOC concentration influenced CH production potential indirectly via complementarity of methanogenic evenness (dominance) and available phosphorus (AP). Increasing SOC accumulation improved AP release and stimulated CH production when SOC was at a low level, whereas decreased evenness and suppressed CH production when SOC was at a high level. A nonlinear relationship was detected between SOC and CH production potential, and CH production potential decreased when SOC was ≥14.16 g kg. Our results indicated that the higher SOC sequestration can not only mitigate CO emissions directly but CH emissions indirectly, highlighting the importance to enhance SOC sequestration using optimum agricultural practices in a rice-wheat cropping system.