Novel Glomeromycotina-Moss Associations Identified in California Dryland Biocrusts

Drylands, which comprise ~45% of Earths land area, host biological soil crusts (biocrusts)--symbiotic communities of cyanobacteria, fungi, algae, lichen, and bryophytes that stabilize soil and support key ecosystem functions. Moss dominated biocrusts in particular are interesting due to their potential to illuminate ancient bryophyte-fungal interactions, but their associated microbial communities remain poorly characterized. To test the hypothesis that mosses in biocrusts harbor specific fungal associates, we conducted amplicon metabarcoding and microscopic surveys employing fungal staining across an aridity gradient. We identified novel associations between mosses and arbuscular mycorrhizal fungi (AMF), with phylogenetic analyses revealing distinct fungal communities in moss biocrusts compared to adjacent bare soil. Intracellular branching by fungi resembling Glomeromycotina was observed within healthy Trichostomopsis australaceae cells, suggesting interactions beyond saprotrophy. Moreover, shifts in AMF community composition along an aridity gradient highlight the potential vulnerability of biocrust mycobiomes to climate change. These findings provide critical insights into ancient bryophyte-fungal symbioses, potentially analogous to those enabling early land plant colonization during the Ordovician (~470 Ma). They also underscore the need to understand and protect biocrust microbial communities as aridity intensifies under climate change.