Diversity and co-occurrence networks of bacterial and fungal communities on two typical debris-covered glaciers, southeastern Tibetan Plateau

Abstract

Debris-covered glaciers (DCGs) are globally distributed and thought to contain greater microbial diversity than clean surface continental glaciers, but the ecological characteristics of microbial communities on the surface of DCGs have remained underexplored. Here, we investigated bacterial and fungal diversity and co-occurrence networks on the supraglacial debris habitat of two DCGs (Hailuogou and Dagongba Glaciers) in the southeastern Tibetan Plateau. We found that the supraglacial debris harbored abundant microbes with Proteobacteria occupying more than half (51.5%) of the total bacteria operational taxonomic units. The composition, diversity, and co-occurrence networks of both bacterial and fungal communities in the debris were significantly different between Hailuogou Glacier and Dagongba Glacier even though the glaciers are geographically adjacent within the same mountain range. Bacteria were more diverse in the debris of the Dagongba Glacier, where a lower surface velocity and thicker debris layer allowed the supraglacial debris to continuously weather and accumulate nutrients. Fungi were more diverse in the debris of the Hailuogou Glacier, which experiences a wetter monsoonal climate, is richer in calcium, has greater debris instability, and greater ice velocity than the Dagongba Glacier. These factors may provide ideal conditions for the dispersal and propagation of fungi spores on the Hailuogou Glacier. In addition, we found an obvious gradient of bacterial diversity along the supraglacial debris transect on the Hailuogou Glacier. Bacterial diversity was lower where debris cover was thin and scattered and became more diverse near the glacial terminus in thick, slow-moving debris. No such increasing bacterial pattern was detected on the Dagongba Glacier, which implies a positive relationship of debris age, thickness, and weathering on bacterial diversity. Additionally, a highly connected bacterial co-occurrence network with low modularity was found in the debris of the Hailuogou Glacier. In contrast, debris from the Dagongba Glacier exhibited less connected but more modularized co-occurrence networks of both bacterial and fungal communities. These findings indicate that less disturbed supraglacial debris conditions are crucial for microbes to form stable communities on DCGs.