Highly heterogeneous mycobiota shape fungal diversity in two globally distributed lichens

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 mycobiota. Because lichen mycobiota diversity is still largely unknown, we aimed to characterize it in two cosmopolitan lichens, Rhizoplaca melanophthalma and Tephromela atra. The mycobiota were investigated across a broad distribution using both a culture-dependent approach and environmental DNA metabarcoding. The variation of the mycobiota associated with the two lichen species was extremely high, and a stable species-specific core mycobiota was not detected with the methods we applied. Most taxa were present in a low fraction of the samples, and no fungus was ubiquitously present in either lichen species. The mycobiota are thus composed of heterogeneous fungi, and some taxa are detectable only by culture-dependent approaches. We suspect that lichens act as niches in which these fungi may exploit thallus resources and only a few may establish more stable trophic relationships with the major symbiotic partners.