Catchment characteristics and seasonality control the composition of microbial assemblages exported from three outlet glaciers of the Greenland Ice Sheet

Drivers of Epilithic Biofilms in Greenland Streams: The Role of Nutrients, Temperature and Catchment Slope Across a Climate Gradient

The Arctic is warming faster than the global average, making it critical to understand how this affects ecological structure and function in streams, which are key Arctic ecosystems. Microbial biofilms are crucial for primary production and decomposition in Arctic streams and support higher trophic levels. However, comprehensive studies across Arctic regions, and in particular within Greenland, are scarce. This study analysed total biomass, autotrophic biomass (chlorophyll a), and the general structure of major autotrophic groups in stream epilithic biofilms across Greenland's subarctic, Low Arctic, and High Arctic regions. Our aim was to identify primary environmental drivers of biofilm across these climate regions. We observed large environmental variation differences in biofilm chlorophyll a concentrations and total biomass across the regions. Cyanobacteria, diatoms, and green algae were present in all regions, with cyanobacteria dominating High Arctic streams. Phosphate and water temperature primarily drove autotrophic biofilm abundance measured as chlorophyll a concentration, while catchment slope and nitrate concentrations influenced total biofilm biomass, with relationships varying by region. Our results suggest increased biofilm accumulation in Greenland streams under projected climate warming, which likely will alter trophic food webs and biogeochemical cycling, with region-specific responses expected.

Distinct influences of altitude on microbiome and antibiotic resistome assembly in a glacial river ecosystem of Mount Everest

The profound influences of altitude on aquatic microbiome were well documented. However, differences in the responses of different life domains (bacteria, microeukaryotes, viruses) and antibiotics resistance genes (ARGs) in glacier river ecosystems to altitude remain unknown. Here, we employed shotgun metagenomic and amplicon sequencing to characterize the altitudinal variations of microbiome and ARGs in the Rongbu River, Mount Everest. Our results indicated the relative influences of stochastic processes on microbiome and ARGs assembly in water and sediment were in the following order: microeukaryotes < ARGs < viruses < bacteria. Moreover, distinct assembly patterns of the microbiome and ARGs were found in response to differences in altitude, the latter of which shift from deterministic to stochastic processes with increasing differences in altitude. Partial least squares path modeling revealed that mobile genetic elements (MGEs) and viral β-diversity were the major factors influencing the ARG abundances. Taken together, our work revealed that altitude-caused environmental changes led to significant changes in the composition and assembly processes of the microbiome and ARGs, while ARGs had a unique response pattern to altitude. Our findings provide novel insights into the impacts of altitude on the biogeographic distribution of microbiome and ARGs, and the associated driving forces in glacier river ecosystems.

Methylotrophic Communities Associated with a Greenland Ice Sheet Methane Release Hotspot

Subglacial environments provide conditions suitable for the microbial production of methane, an important greenhouse gas, which can be released from beneath the ice as a result of glacial melting. High gaseous methane emissions have recently been discovered at Russell Glacier, an outlet of the southwestern margin of the Greenland Ice Sheet, acting not only as a potential climate amplifier but also as a substrate for methane consuming microorganisms. Here, we describe the composition of the microbial assemblage exported in meltwater from the methane release hotspot at Russell Glacier and its changes over the melt season and as it travels downstream. We found that a substantial part (relative abundance 27.2% across the whole dataset) of the exported assemblage was made up of methylotrophs and that the relative abundance of methylotrophs increased as the melt season progressed, likely due to the seasonal development of the glacial drainage system. The methylotrophs were dominated by representatives of type I methanotrophs from the Gammaproteobacteria; however, their relative abundance decreased with increasing distance from the ice margin at the expense of type II methanotrophs and/or methylotrophs from the Alphaproteobacteria and Betaproteobacteria. Our results show that subglacial methane release hotspot sites can be colonized by microorganisms that can potentially reduce methane emissions.