Highly heterogeneous mycobiomes shape fungal diversity in two globally distributed lichens

Premise — Lichens are multi-kingdom symbioses in which fungi, algae and bacteria interact to develop a stable selection unit. In addition to the mycobiont forming the symbiosis, fungal communities associated with lichens represent the lichen mycobiome, but their taxonomic and functional diversity across the range of their host lichens is still largely unknown. We aim to characterize the diversity of the lichen mycobiome in two cosmopolitan lichens, i.e. Rhizoplaca melanophthalma and Tephromela atra as study models. Methods — The mycobiomes were investigated across a broad range of their distribution using both a culture-dependent approach and environmental DNA. Key results — The variation of the mycobiomes associated with the two lichen species is extremely high, and a stable species-specific core mycobiome is hardly identifiable. Most of the mycobiome taxa are present in a low fraction of the samples. No taxon is ubiquitously present in neither lichen species. The mycobiomes of R. melanophthalma and T. atra are thus composed of heterogenous lichenicolous fungi. A fraction of these mycobiomes is also generalist, as it associates with both lichens. A fraction of the two lichen mycobiomes is detectable only by the culture-dependent approach and escapes PCR amplification. Conclusions — Lichens rather are reservoirs of other fungi that choose the thalli as own ecological niche to thrive in more extreme habitats..