The Establishment of a Terrestrial Macroalga Canopy Impacts Microbial Soil Communities in Antarctica.

Prasiola is a genus of foliose green algae that forms extensive cryptogamic canopies that contribute to the greening of ice-free areas in the Antarctic tundra. To better understand the impact of Prasiola canopy establishment on colonization in these areas, this study compared the taxonomic and functional structures of bacterial and fungal communities in adjacent soils with and without extensive Prasiola colonization. DNA metabarcoding was employed to analyze the microbial community structure in these soils and in the canopy. Additionally, a phylogenetic study of Prasiola samples was conducted to characterize the taxonomic composition of the analyzed canopies, revealing the presence of Prasiola crispa (Lightfoot) Kützing and P. antarctica Kützing. Key soil attributes were assessed to examine the canopy's influence. Higher pH and carbon, nitrogen, and organic matter contents were found in Prasiola-covered soils than in bare soils. Furthermore, Prasiola canopy establishment not only influenced abiotic soil properties but also shaped soil microbial community structure and its functions. For instance, while Actinobacteriota predominated in bacterial communities both within the Prasiola canopy and beneath it, Bacteroidota dominated in the bare soil. Despite significant variability across soil types, fungal communities showed a trend of higher abundances in certain Ascomycetes, such as Helotiales, Hypocreales, or Xylariales, in soils beneath Prasiola compared to bare soils. Regarding functional diversity, covered soils exhibited a statistically significant lower potential for bacterial methanogenesis and autotrophic CO₂ fixation compared to bare soils. Finally, lichenized fungi, plant pathogens, and fungal wood saprotrophs tended to be more abundant in covered soils.