Revealing the seed-associated microbiomes of the high mountain plant Acaena macrocephala across an elevational gradient in the southern Andes

The South American Andes are characterized by extreme environmental conditions, including high ultraviolet radiation, marked temperature fluctuations, and low nutrient availability, which impose strong constraints on plant establishment. These abiotic stressors have driven plant species to evolve diverse survival strategies, including the establishment of beneficial interactions with native microbial communities that enhance their adaptive capacity. In this study, we characterized the bacterial and fungal communities associated with the seeds of Acaena macrocephala , a high-elevation forb inhabiting the mountains of south-central Chile. Seeds were collected along an elevational gradient on the Batea Mahuida Plateau (Araucanía Region, south-central Chile), including low (1,390 m a.s.l.), mid (1,715 m a.s.l.), and high (1,934 m a.s.l.) elevations. Seed-associated bacterial and fungal microbiomes were profiled using amplicon sequencing of the 16 S rRNA gene and fungal ITS region to assess microbial diversity and community composition. Bacterial alpha diversity was lower at the low-elevation site than at the mid- and high-elevation sites, whereas fungal alpha diversity did not differ among elevations. Community composition differed significantly along the elevational gradient for both microbial groups, although the effect of elevation was more pronounced in bacterial communities. Bacterial communities at low and mid elevations were dominated by the genus Sodalis and the families Pectobacteriaceae and Morganellaceae , whereas fungal communities were consistently dominated by the genera Eremothecium , Holleya , and Cladosporium and the family Saccharomycetaceae across all elevations. These patterns, representing the first characterization of seed-associated microbiomes in these ecosystems, suggest that seed-associated microbiomes constitute a reservoir of functional microorganisms that may contribute to the adaptation and persistence of A. macrocephala in harsh high-Andean environments.