Functional Diversity and Community Composition of Soil Fungi Associated With Canopy Dieback in Araucaria araucana...

Soil fungal communities play vital roles in forest ecosystem functioning, yet their relationship with tree health remains insufficiently characterized in many endangered species.

This study, investigated the composition and functional structure of soil fungi associated with symptomatic and asymptomatic individuals of Araucaria araucana in the Nahuelbuta Coastal Range, Chile.

Using high-throughput ITS1 sequencing and trait-based annotation, we compared fungal assemblages across two forest sectors with contrasting edaphic conditions.

Marked differences in taxonomic and functional composition were observed between sites, with more even and functionally diverse communities in less restrictive soils. Within this site, where both tree health conditions co-occur, no significant differences in alpha or beta diversity were detected; nevertheless, species-level and functional guild analyses revealed shifts in composition. A shared core microbiome included taxa putatively identified as endophytes, including Cladophialophora minutissima, Fraxinicola europaea, Linnemannia hyalina, saprotrophs (Solicoccozyma terricola, Helicodendron conglomeratum, Pseudogymnoascus roseus) and a plant pathogen (Penicillium excelsum). Symptomatic trees harboured unique stress-tolerant taxa, including cold-adapted saprotrophs and ericoid mycorrhizal fungi, while asymptomatic trees supported lignocellulose decomposers, mutualists and early-successional symbionts.

The observed fungal shifts suggest that canopy dieback is associated with a functional reorganization of the rhizosphere microbiome rather than a simple loss of diversity.

These findings provide new insights into the fungal ecology of A. araucana forest and contribute to understanding how soil microbiomes respond to forest decline under contrasting edaphic conditions.