Antarctic rocky outcrops as microbial diversity and biogeochemical hotspots.

Climate-driven deglaciation is rapidly exposing rocky outcrops in polar-alpine landscapes, creating novel habitats for organisms. Yet, the contribution of these new habitats to microbial diversity and biogeochemical processes remains largely overlooked. Here, we assessed how Antarctic rocky outcrops shape soil microbial diversity, organic matter formation, and nutrient cycling by comparing thin soils developed on rocky outcrops with soils from surrounding areas on Livingston Island, Antarctica. In these soils, we characterized bacterial and fungal communities, organic matter composition and extracellular enzyme activities using high-throughput sequencing, pyrolysis-GC/MS and enzyme assays. Outcrop soils exhibited higher nutrient content and moisture, creating resource-rich microhabitats that supported distinct microbial communities shaped by strong habitat filtering. Bacterial communities differed mainly in composition, whereas fungal communities in outcrop soils showed higher local diversity and included specialized functional groups such as decomposers, contributing to greater functional capacity. Outcrop soils were also enriched in fresh, labile organic matter compared with the more transformed organic matter in surrounding soils, indicating contrasting soil development pathways. Overall, Antarctic rocky outcrops act as microbial and biogeochemical hotspots, fostering distinct functional microbial assemblages and enhancing organic matter build-up and nutrient cycling. As deglaciation advances, these microhabitats may influence microbial diversity and resource availability at the landscape scale.