Microbial mechanisms underlying differences of methane emissions between urban and rural wetlands

Abstract

Methane (CH₄) emissions differ between urban and rural wetlands, while the microbial mechanisms associated with these differences have not been clearly identified. Here, we characterized the CH₄-cycling microbial communities and their functional function metabolic pathways between urban and rural wetlands by using 16S rRNA amplicon sequencing, metagenomes and CH₄ flux measurements. Results showed that rural wetlands primarily utilized acetate/CO₂-dependent methanogenic pathway and complete carbon oxidation to CO₂ in methanotrophic pathway. Whereas, urban wetlands were dominated by the coenzyme M-dependent methanogenic pathway and trimethylamine catabolism, with methanotrophic pathway characterized by enhanced carbon assimilation capacity. In wetland water, while the abundances of methanogens in urban water were 5-fold lower than in rural water, urban water exhibited stronger microbial cooperation and higher metabolic flexibility, which were associated with an 85% higher water-atmosphere CH₄ flux compared to rural counterparts. In wetland soil, key environmental factors (e.g. higher pH and lower organic matter content compared to rural sites) shaped distinct microbial community structures and CH₄ metabolic traits. These differences were shown as higher functional gene diversity, more stable co-occurrence networks, and greater metabolic flexibility, which were linked to a 6-fold higher soil CH₄ emissions than in rural soil. This study describes the microbial mechanisms underlying CH₄ emission differences between urban and rural wetlands, providing insights into microbially mediated CH₄ cycling in urban wetland ecosystems.