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

Abstract

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.