Soil Methane Emission Effects and Microbial Mechanisms of Rice Field Soils with Different Rice Straw Application Rates over 13 Consecutive Years

This significantly increases the abundance of methanogenic functional genes (mcrA) (with average increases of 2.5, 3.8, and 3.6 times compared to S0 for S1, S2, and S3, respectively) and enriches the Methanosarcinaceae family, which metabolizes multiple substrates, leading to a substantial increase in CH4 production potential (S3 increased by 246% compared to S0). Although the abundance and oxidation potential of methanotrophic functional genes (pmoA) also increased, the growth was far lower than the production potential, resulting in a metabolic imbalance of “more production than oxidation”, further exacerbating net CH4 emissions.

Although S3 could enhance soil carbon sequestration rates, it had the highest mitigation benefit offset rate (12.93). In contrast, under conditions where there was no significant difference in mitigation benefit offset rates, S1 achieved the lowest CH4 emission coefficient (5.05%), while S2 achieved the highest carbon sequestration rate (2.27 t CO2-eq t·hm-2·a-1), indicating that moderate straw returning optimally synergizes carbon sequestration and emission reduction. 【Conclusion】The results of this study reveal that moderate straw returning is a key measure to reconcile the contradiction between “carbon sequestration” and “emission reduction” in rice paddies.