Glacier retreat threatens unique microbial communities and biogeochemical functions confined to glacier surfaces

Glaciers are rapidly retreating under climate warming, with potential loss of unique microbial ecosystems. Here, we investigated bacterial and fungal communities across the glacier surface and foreland of the Arklio Glacier, Canadian High Arctic, using 16S and ITS amplicon sequencing. Both bacterial and fungal communities on the glacier were distinct and largely independent from those in the foreland, indicating limited microbial dispersal and strong environmental filtering. Alpha diversity patterns revealed opposite trends between the two groups: bacterial diversity increased toward the glacier terminus, whereas fungal diversity declined. In the foreland, bacterial diversity peaked around 100 m (~ 20 years post-retreat), while fungal diversity reached a maximum at 20 m, suggesting distinct successional responses to deglaciation. Functional predictions indicated contrasting metabolic strategies: phototrophy dominated on glacier ice, whereas chemoheterotrophy and nitrification prevailed in foreland soils. Together, these results demonstrate that glacier retreat reshapes both microbial composition and function, and underscore how glaciers are threatened reservoirs of microbial biodiversity.