Fungal diversity in Atlantic oak root systems: a pioneering study in the Cantabrian Mountains

Abstract

Oak forests are native ecosystems that support diverse life forms and provide essential services. This study focused on elucidating the taxonomic characterization and diversity of fungal species in Atlantic oak woodlands dominated by Quercus petraea at its southwestern distribution limit in the Iberian Peninsula. Sampling was conducted in three protected natural areas to assess fungal root diversity by macroscopic and microscopic methods, including histological analysis of root sections. Additionally, metabarcoding techniques were used to sequence the internal transcribed spacer (ITS) region, targeting fungal diversity. The analysis identified 1,043 Amplicon Sequence Variants (ASVs), corresponding to 297 species. Although fungal richness was consistent across locations, community composition was geographically specific. Tree social classes also influenced fungal diversity, which was higher in the intermediate trees in some areas. Functional guilds varied markedly, with symbiotic fungi (notably ectomycorrhizal fungi and dark septate endophytes) most abundant based on sequencing reads, while saprotrophs were the most diverse genus. These findings highlight the structural and ecological complexity of oak-associated fungal communities and their potential importance in forest conservation and ecosystem functioning.