So far but so close: the biogeography of soil and plant-associated fungi in one of the most remote landmasses on Earth.

The Kerguelen Islands, one of the most isolated lands on Earth, represent an ideal open-air laboratory to explore patterns of microbial biogeography under minimal human influence. Fellfields, in particular, are near pristine habitats dominated by endemic plant species with few introduced ones. Using metabarcoding, we characterized 70 bulk soil and 70 root-associated fungal communities from two native plant species and one introduced one, in four distant fellfield sites. Comparative analyses of Kerguelen fungal sequences with global reference databases (GlobalFungi and UNITE) revealed that 60% to 76% of the recovered operational taxonomic units (OTUs) had a close match at ≥97% sequence identity, which indicates the presence of a majority of species with wide distribution ranges that have already been observed elsewhere on the globe. Although evidence of endemism is difficult to establish, haplotype networks created for OTUs already observed elsewhere in the world illustrate in a number of cases the presence of dominant amplified sequenced variants specific to Kerguelen, suggesting intraspecific endemism. A global analysis of the already known fungal OTUs showed they were predominantly associated to high-latitude and cold environments. A spatial analysis further affiliated known Kerguelen's fungi to two distinct endemicity zones, one that encompassed Southern South America/Antarctic Peninsula and one in Central and Northern Europe that potentially contributed to alien species that may have invaded this remote archipelago. Our results indicate that the mycoflora of one of the most isolated islands in the world has been shaped by repeated episodes of colonization from different parts of the globe.