Methane Cycling in Alpine River-Reservoir Systems: Insights into Microbe-Mediated Mechanisms

Abstract

Reservoir impoundment alters riverine habitats and biogeochemical cycling, influencing diffusive methane (CH₄) fluxes and regional effects. Research on plain rivers and reservoirs is well established, but studies on CH₄ dynamics and drivers in high-altitude river-reservoir ecosystems remain scarce. This study combined field sampling, monitoring, and metagenomic sequencing at Guoduo Reservoir (upper Zhaqu River, Lancang Basin). The results showed that diffusive CH₄ fluxes in the reservoir section (105.25 ± 21.62 μmol·m^–2·d^–1) were significantly higher than those in adjacent tributaries (39.97 ± 6.99 μmol·m^–2·d^–1) and the upstream natural river reach (11.24 ± 1.87 μmol·m^–2·d^–1). Sediment metagenomic analyses revealed that acetoclastic methanogenic archaea dominated the reservoir sediments, and genomes of Methanothrix harbored complete gene sets encoding key enzymes for acetoclastic methanogenesis. Lowest upstream diffusive CH₄ fluxes were linked to aerobic methanotrophs (e.g., Methylobacterium) that oxidize CH₄ and suppress net emissions. Co-occurrence network analysis revealed strong synergies between methane-cycling microorganisms and functional groups (e.g., Proteobacteria, Actinobacteria) that jointly regulate diffusive CH₄ fluxes. The findings reveal the mechanisms of enhanced diffusive CH₄ emissions from plateau reservoirs, aiding the understanding of carbon cycling and greenhouse gas assessments.