Long-term fertilization enhances the activity of anaerobic oxidation of methane coupled to nitrate reduction and associated microbial abundance in paddy soils

Abstract

Anaerobic oxidation of methane coupled to nitrate reduction (nitrate-coupled AOM) is performed by Candidatus Methanoperedens nitroreducens (M. nitroreducens)-related archaea, and is recently recognized as a crucial component of the global carbon cycle. The input of fertilizers is an essential agricultural practice that greatly impacts methane (CH₄) production and emission. However, the significance of nitrate-coupled AOM in CH₄ cycling and its response to fertilization in rice fields remain unclear. In this study, the potential nitrate-coupled AOM rates and the communities of M. nitroreducens-related archaea in rice fields were examined at different soil layers (0–10, 10–20, and 30–40 cm) at tillering, elongation, flowering, and ripening stages under three long-term fertilization treatments (CK-without fertilizer, CF-chemical fertilization, or CFS-chemical fertilization with straw incorporation). The results indicated that both CF (1.07 nmol ¹³CO₂ g⁻¹ d⁻¹) and CFS (1.21 nmol ¹³CO₂ g⁻¹ d⁻¹) treatments significantly promoted the potential nitrate-coupled AOM rates compared to CK (0.53 nmol ¹³CO₂ g⁻¹ d⁻¹). A greater response of potential activity to fertilization was observed at plough layer (upper 20 cm) and during elongation stage. The abundance of M. nitroreducens-related archaea under CF (1.12 × 10⁷ copies g⁻¹) and CFS (1.62 × 10⁷ copies g⁻¹) treatments was significantly greater than that under CK (6.93 × 10⁶ copies g⁻¹). Conversely, the growth response of these archaeal to fertilization was stronger at deeper layer (30–40 cm). Moreover, no significant change was observed in the community composition of M. nitroreducens-related archaea among treatments. Correlation analysis suggested that the variations of soil organic carbon, NH₄⁺, and NO₃⁻ contents caused by fertilization were key factors influencing the potential nitrate-coupled AOM rates and M. nitroreducens-related archaeal abundance. Our findings provide the first evidence for positive response of nitrate-coupled AOM to long-term fertilization, demonstrating its potential to act as an important process for mitigating CH₄ emission in rice fields.