Contrasting nutrient retention in alpine soils: the role of soil microbiome in phosphorus and nitrogen mobility in scree and meadow environments.

Alpine catchments encompass heterogeneous soil habitats with varying roles in nutrient cycling. While undeveloped till soils in scree areas are hotspots for nitrate and phosphate leaching, vegetated alpine meadow soils rather efficiently retain nutrients. This study examines the role of microbial communities in nutrient mobilization and retention, beyond the effects of abiotic soil properties. We compared the chemical, microbial, and functional characteristics of scree and meadow soils in four high-elevation catchments of the Tatra Mountains in Central Europe. Despite their lower organic matter content and microbial biomass, scree soils exhibited high concentrations of mobile nitrate and phosphate, low phosphate sorption ability, and significantly greater phosphorus leaching. Their microbiomes were distinct and enriched with pioneer taxa, including lichenized fungi, oligotrophic bacterial lineages (e.g. AD3 and Eremiobacteria), and saprotrophic fungi that specialize in the recycling of microbial necromass. These microbiomes exhibited high biomass-specific activities related to nutrient mobilization. In contrast, meadow soils supported larger microbial communities dominated by fungi with strong plant associations and functional traits that enhance nutrient retention. Our findings demonstrate that soil microbiota actively control nitrogen and phosphorus mobility by acting as either accelerators (in vegetation-free scree areas) or buffers (in meadows) of nutrient leaching from alpine soils.