Silicon (Si) fertilizer application has been observed reduce nitrous oxide (N2O) emissions in paddy soil. However, the responses of microbial communities remain poorly understood. In this study, we conducted a microcosm experiment with three Si application levels: CK (0 mg kg−1, SiO2), Si1 (100 mg kg−1, SiO2), and Si2 (200 mg kg−1, SiO2) under two soil moisture conditions-Flooding (125 % w/w) and Drying (60 % w/w). The abundance and the microbial community structure of nirK, nirS for N2O production, nosZ I and nosZ II for N2O reduction were analyzed. Under flooding condition, Si2 reduced N2O emissions by 87.1 %, this mitigation effect weakened to 52.9 % under drying. Microbial community structure rather than size was regulated by Si application. N2O-reducing microbial communities were strongly influenced by Si amendment, only nirS-containing denitrifier was observed in N2O production process. Relative abundance of genus Noviherbaspirillum was typically depressed by Si application and positively correlated with N2O flux. Several genera, such as Pleomorphomonas, Achromobacter, Intrasporangium were identified as crucial mediators of N2O reduction process. Co-occurrence network analysis indicated greater complexity in the N2O-reducing microbial communities in response to Si application. PLS-SEM reveals different mechanisms of Si depress N2O flux in different soil moisture. Under flooding condition, the N2O mitigation effect of Si was primarily driven by microbial processes. While under drying condition, the mitigation effect was dominated by a strong abiotic-chemical pathway. These insights contribute to a mechanistic understanding of how Si management can be optimized for N2O mitigation in paddy soil.
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