Methane cycling in typical emerging proglacial lakes on the Tibetan Plateau: Insights into the metabolic mechanisms mediated by microorganisms.

A large number of high-latitude emerging proglacial lakes have formed on the Tibetan Plateau (TP) due to the global warming and deglaciation. These lakes have the potential to emit methane (CH4) because of the exposure of cryopreserved organic carbon, leading to their significance in regional carbon turnover and cycling. However, previous studies have focused more on human-impacted lakes (e.g., eutrophic lakes), resulting in limited research on the mechanisms of CH4 cycling in the proglacial lakes. In this study, we demonstrated that three typical emerging high-latitude proglacial lakes (∼5500 m a.s.l.) on the TP exhibited a diffusive emission flux of 32.39 ± 11.66 μmol/m2/d during the summer. The δ13C-CH4 values (-50.10 ± 0.56‰) suggested a biogenic origin of CH4 through the acetoclastic pathway in the lakes. Metagenome sequencing further showed that microbes involved in methanogenesis were dominated by Methanosarcina (36.74 ± 0.07 % of total methanogens). Significant CH4 consumption was observed in the proglacial lakes. The microbes involved in the CH4 consumption were dominated by Methylobacter (48.50 ± 0.17 % of total methanotrophs). A Mantel test demonstrated that dissolved iron (Fe) was a key factor controlling the structure of the CH4 cycling microbial communities. Functional gene and co-occurrence network analyses indicated that members of Pseudomonadota, Bacteroidota, and Actinomycetota may be involved in CH4 cycling by providing methanogenic substrates (i.e., acetyl coenzyme A) and consuming CH4 oxidative intermediates (i.e., methanol, formaldehyde, and formic acid). This study emphasized the ecological significance of emerging proglacial lakes in CH4 releases. It broadened the current understanding of cryophilic CH4 cycling microbes and their mechanisms, that enhances our knowledge of the carbon cycle on the TP.