Soil fungal diversity and assembly in an endangered high-altitude Neotropical grassland

Abstract

The Southern Brazilian Highland Grasslands are one of the few subtropical high-altitude grasslands in the Neotropics, featuring highly endemic biodiversity. Yet, this formation remains largely neglected in conservation policies and faces several anthropogenic pressures, despite being part of the Brazilian Atlantic Forest global biodiversity hotspot. While plant communities are well understood in this formation, its soil funga is completely unknown. For the first time, we characterized the diversity of soil fungal communities in these grasslands, using shotgun metagenomics to generate ITS and 18S profiles, assess potential composition of trophic modes, and predict functionality based on detected genes across three preserved grassland fragments. We also sought to unveil how fungal communities are shaped by different assembly processes at a local scale. Ascomycota dominated across the 16 detected phyla, while Basidiomycota and Chytridiomycota showed lower but consistent relative abundances, a pattern that holds for order and genus levels. Taxonomic profiles indicated that saprotrophs and plant pathogens have homogenous relative abundances across fragments, with genes revealing a metabolic potential consistent with this pattern. However, community structures were significantly different among fragments, which also showed distinct alpha diversity patterns. Edaphic and plant community-related variables commonly known to modulate soil fungal communities explained a small portion of the variance observed in communities. In accordance, we showed that stochastic and deterministic community assembly processes have contrasting dominance within and across fragments. This indicates asymmetric connectivity between grassland patches and complex community assembly dynamics at small scales, which can be linked to the mosaic patterns formed between grasslands and adjacent formations. Our findings establish a baseline for soil fungal diversity across local Southern Brazilian Highland Grasslands fragments and highlight the need to integrate overlooked, yet diverse, fungal communities into conservation planning for this endangered formation.