Denitrifying Anaerobic Methane Oxidation Activity and Microbial Mechanisms in Riparian Zone Soils of the Yulin River, a Tributary of the Three Gorges Reservoir

Riparian zones are recognized as major sources of greenhouse gas emissions, particularly methane (CH₄). Denitrifying anaerobic methane oxidation (DAMO) has garnered growing attention due to its significant contribution to mitigating CH₄ emissions in wetland environments. Nonetheless, the specific role and microbial mechanisms of DAMO in controlling CH₄ release within riparian zones are still not well comprehended. This study employed isotopic labeling experiments to measure the nitrate-dependent anaerobic methane oxidation (NaDAMO) and nitrite-dependent anaerobic methane oxidation (NiDAMO) potential of soil samples from riparian zones that were collected during different hydrological cycles. Moreover, soil physicochemical properties, DAMO activity, and microbial abundance were integrated to analyze the key factors and mechanisms influencing DAMO in riparian zone soils. The isotope tracer results showed that NaDAMO activities (1.4–11.93 nmol ¹³CO₂ g^-1day^-1) were significantly higher than NiDAMO activities (0.66–9.19 nmol ¹³CO₂ g^-1day^-1) in the riparian zone (p<0.05). NiDAMO activities were more strongly influenced by hydrological variations compared to NaDAMO activities, exhibiting higher levels during the discharge period (2.78–9.19 nmol ¹³CO₂ g^-1day^-1) compared to the impoundment period (0.66–4.10 nmol ¹³CO₂ g^-1day^-1). The qPCR analysis showed that the gene copies of NaDAMO archaeal mcrA (10⁷ copies g^-1) were approximately ten times greater than those of NiDAMO bacterial pmoA (10⁶ copies g^-1) in the majority of the sampling sites. Correlation analyses revealed that NiDAMO activity was influenced by soil pH (p<0.05), while NaDAMO microbes were influenced by temperature, organic carbon, and ammonia nitrogen concentrations (p<0.05). In summary, this research explored how hydrological changes in the riparian zone influence DAMO activities and their underlying mechanisms, providing a theoretical basis for mitigating CH₄ emissions in riparian zones of reservoir regions.