A Multi-Proxy Approach Links Pedological Context to Fungal Community Variation in Temperate Mountain Forest Soils

Soil fungi play a key role in nutrient cycling and soil organic matter turnover, yet the influence of pedological context on fungal communities across forest types remains insufficiently understood. Here, we combined soil chemical analyses, Fourier-transform infrared spectroscopy (FTIR), and ITS2 metabarcoding to investigate soil properties and fungal communities in temperate mountain beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst) forests in Italy developed on contrasting geological substrates. Soil horizons were sampled across seasons to characterize the main associations between fungal community structure, inferred functional diversity, and environmental context. Soil chemistry revealed site- and horizon-dependent patterns, particularly in pH, Ca, and P availability, whereas differences related to dominant tree species were comparatively limited. FTIR spectra showed clear variation in organic matter composition among sites, consistent with site- and stand-associated differences in organic matter composition. Fungal community composition was primarily associated with site and soil horizon. Functional guild patterns suggested ectomycorrhizal dominance in Ca-rich soils and greater prevalence of saprotrophs in more acidic soils. Overall, this multi-proxy approach suggests that pedological context was more closely associated with fungal community structure and ecological strategies than with vegetation type or season within the studied stands. These patterns should be interpreted as site-specific and hypothesis-generating because substrate types were not replicated across independent locations.