Straw mulching combined with alternate wetting and drying reduces methane emissions in paddy fields: associations with carbon availability and methanogenic archaeal community shifts.

内容摘要

Rice paddies are a major source of agricultural methane (CH4) and nitrous oxide (N2O) emissions, making the optimization of straw return practices and water management critical for greenhouse gas mitigation. A two-year field experiment (2021-2022) evaluated the combined effects of three wheat-straw return modes (no return, S0; mulching, S1; incorporation, S2) and two irrigation regimes (continuous flooding, W1; alternate wetting and drying, W2) on CH4 and N2O emissions, heading-stage soil organic carbon (SOC) and dissolved organic carbon (DOC), methanogenic archaeal communities, and rice grain yield. The CH4-mitigating effect of W2 was strongly contingent on straw return mode. The S1W2 treatment achieved the lowest cumulative CH4 emissions and global warming potential (GWP), reducing cumulative CH4 and GWP by 44.9% and 39.6% relative to S0W2, and attained the lowest greenhouse gas intensity (GHGI) at 0.20 kg CO2-eq kg-1 grain yield without compromising rice yield. By contrast, S2W2 generated the highest CH4 and N2O emissions, with cumulative CH4 under S2W2 exceeding that under S2W1 by 2.64-fold in 2021 and 1.37-fold in 2022. Methanogenic archaeal communities were dominated by Methanobacterium and Methanosphaera. Under W2, α-diversity and community composition shifted markedly among treatments; however, these compositional changes were not directly proportional to CH4 fluxes, indicating that taxonomic patterns cannot be equated with methanogenic functional activity. N2O emissions were primarily associated with water management, with straw return mode playing a comparatively limited role. Overall, S1W2 offers a promising agronomic pathway toward lower rice-season paddy greenhouse gas intensity, and these outcomes were associated with differences in carbon availability and soil redox conditions across treatments.