Increased aridity is associated with diversity and composition changes in the biocrust mycobiome

Drylands comprise 45% of Earths land area and contain ecologically critical soil surface communities known as biocrusts. Biocrusts are composed extremotolerant organisms including cyanobacteria, microfungi, algae, lichen, and bryophytes. Fungi in biocrusts help aggregate these communities and may form symbiotic relationships with nearby plants. Climate change threatens biocrusts, particularly moss biocrusts, but its effects on the biocrust mycobiome remain unknown. Here, we performed a culture-dependent and metabarcoding survey of the moss biocrust mycobiome across an aridity gradient to determine whether local climate influences fungal community composition. As the local aridity index increased, fungal communities exhibited greater homogeneity in beta diversity. At arid and hyper-arid sites, communities shifted toward more extremotolerant taxa. We identified a significant proportion of fungal reads and cultures from biocrusts that could not be classified. Rhodotorula mucilaginosa and R. paludigena were significantly enriched following surface sterilization of healthy biocrust mosses. This aligns with their known roles as plant endophytes. We also observed septate endophyte colonization in the photosynthetic tissues of mosses from arid climates. Collectively, these results suggest that the biocrust mycobiome will undergo significant shifts in diversity due to climate change, favoring extremotolerant taxa as climate conditions intensify. The survey results also highlight taxa with the potential to serve as bioinoculants for enhancing biocrust resilience to climate change. These findings offer valuable insights into the potential impacts of climate change on drylands and provide crucial information for biocrust conservation.