[Characteristics of nitrite-dependent anaerobic methane oxidation activity and microbial community in paddy fields...

Nitrite-dependent anaerobic methane oxidation (N-DAMO) is a critical pathway for mitigating methane (CH₄) emissions from paddy fields. The characteristics of N-DAMO activity and functional microbial communities under combined organic and inorganic nitrogen fertilizer remain unclear. We conducted an experiment with three fertilization treatments, including inorganic nitrogen fertilizer (NPK), combined organic manure and inorganic nitrogen fertilizer (MNPK), and straw return combined with inorganic nitrogen fertilizer (SNPK). We collected soil samples during rice (Nanjing 9108) key growth periods (booting, heading, and maturity periods). Through laboratory slurry incubation combined with stable isotope tracing, high-throughput sequencing, and quantitative PCR (qPCR), we systematically analyzed the variations in N-DAMO activity, gene abundance and community structure of the functional microorganism NC10 bacteria under different fertilization treatments. The results showed that N-DAMO activity ranged from 2.20 to 6.58 nmol CO₂·g^-1·d^-1. The N-DAMO activity at the heading stage under MNPK and SNPK was significantly higher than that under NPK, while there were no significant differences among treatments during other growth periods. The gene abundance of NC10 bacteria ranged from 8.36×10⁶ to 2.77×10⁷ copies·g^-1 dry soil. Under MNPK and SNPK, the gene abundance of NC10 bacteria was significantly higher than that under the NPK, with 53.9% and 27.7% increases, respectively. There were no significant changes in NC10 bacterial community structure among three fertilization treatments. Correlation analysis revealed that soil water content and NH₄ ⁺-N were the primary environmental factors influencing N-DAMO activity in paddy fields. In conclusion, MNPK treatment resulted in the highest NC10 bacterial gene abundance and enhanced N-DAMO activity, exhibiting the greatest potential to mitigate CH₄ emission from paddy fields among the three fertilization treatments.