Metabarcoding of Chloraea orchid roots reveals diverse fungal communities and a negative association between fungal diversity and geographic range.

INTRODUCTION

Orchid mycorrhizal fungi are essential partners for orchid seed germination and survival, yet the full diversity of fungi associated with orchid roots, including nonmycorrhizaltaxa, remains poorly characterized, particularly in the Southern Hemisphere. This could impact orchid conservation and in situ restoration programs. Here we present the first untargeted metabarcoding study of root-associated fungal communities in Chilean terrestrial orchids.

METHODS

We used ITS regsion for fungal metabarcoding, sampling eleven species of the genus Chloraea (Orchidaceae) across the central Chilean coast.

RESULTS

Root-associated communities were dominated by Ascomycota and were highly variable in composition among individuals and species, with orchid mycorrhizal fungi representing only a minor fraction of total diversity and the family Tulasnellaceae absent from all samples. Community composition differed significantly among Chloraea species, and contrary to expectations, species with broader geographic ranges tended to associate with less diverse root-associated fungal communities - a pattern that was consistent in direction across multiple diversity indices but sensitive to sampling effort. A substantial proportion of sequences could not be assigned taxonomically, reflecting the underrepresentation of Chilean fungal diversity in global reference databases.

DISCUSSION: These findings demonstrate the value of untargeted sequencing for revealing the breadth of orchid-fungi associations, and highlight that mycorrhizal specificity could vary markedly across Chloraea species, with direct implications for the conservation of threatened Chilean terrestrial orchids.