Sources and dynamics of microbial communities in cryoconite on an Alpine glacier. Cryoconite on an Alpine glacier

Cryoconite holes, i.e. small ponds that form on glacier surface, are considered the most biologically active environments on glaciers. Ecology of cryoconite holes in polar regions has been widely investigated, while that of cryoconite holes on mountain glaciers has been neglected. In this study we investigated the temporal dynamics of the microbial communities in cryoconite holes on the Forni Glacier (Italian Alps) along the ablation season and the contribution of eolian transport from periglacial environments to the microbial communities of cryoconite holes. We used Next-Generation Sequencing to assess the structure of bacterial communities, and estimated also photosynthesis and respiration rates of cryoconite holes with field measurements. We found a seasonal succession of bacterial communities, with autotrophic populations dominating communities after snow melting, and heterotrophic populations increasing in abundance later in the season. However, communities in cryoconite holes were mainly heterotrophic. Surprisingly, we also observed similarity between communities in cryoconite holes within few tens of meters to one another. Conversely, none of the periglacial environments we investigated (moraines, proglacial plain, and the debris of probable endoglacial origin) hosted bacterial communities similar to those found in the cryoconite holes in any season. Hence, periglacial environments seem not to be the source of bacteria living in the cryoconite, but may provide inputs of organic matter to cryoconite necessary to sustain the heterotrophic communities of cryoconite holes even without affecting the structure of their microbial communities.