Pollution alters methanogenic and methanotrophic communities and increases dissolved methane in small ponds

Highlights: • Ponds with high pollution showed high dissolved CH₄ concentrations. • High pollution altered physicochemical properties and CH₄-cycling microbes. • Interdomain associations between methanogens and methanotrophs were clarified. • Negative associations between dissolved CH₄ and microbial network connectivity. • Physicochemical factors and CH₄-cycling communities affected CH₄ content together. Small ponds have become a hotspot of greenhouse gas emissions, but our understanding of methane (CH₄) cycling and its biological regulation in small polluted ponds remains limited. To assess how pollution affects CH₄ content, we investigated dissolved CH₄ concentrations, water and sediments properties, methanogenic and methanotrophic communities in two types of small polluted ponds. Compared with low pollution (LP) ponds, high pollution (HP) ponds showed significantly (P < 0.05) higher dissolved CH₄ in water. Sequencing of methyl coenzyme M reductase (mcrA) and particulate methane monooxygenase (pmoA) genes showed that HP led to significant (P < 0.05) shifts of CH₄-cycling microbial communities, with increased Shannon index of sediment methanogenic communities and water methanotrophic communities. There were also strong negative associations (P < 0.05) between dissolved CH₄ concentrations and interdomain methanogen-methanotroph network connectivity in water and sediments, respectively. The partial least squares path modeling indicated that dissolved oxygen, total organic carbon, ammonium nitrogen and nitrate nitrogen of water, and total nitrogen and total carbon of sediment, and CH₄-cycling microbes could regulate the CH₄ content. This study clarified the effects of environmental deterioration on CH₄ cycling in small ponds, highlighting the use of methanogen-methanotroph network connectivity to assess the CH₄ production.