Fungal troublemakers – using indicator species with ephemeral fruitbodies to evaluate recovery of formerly extracted raised bogs

Including fungi into nature conservation research allows for a more comprehensive view of habitat quality thanks to their unique role in ecosystems. However, a broad application of fungi as indicators is limited mainly by the ephemeral occurrence of their fruitbodies and insufficient knowledge of their ecology. To overcome these limitations, we searched for fruitbodies of selected fungal peatland indicator species (Arrhenia bigelowii, A. gerardiana, A. telmatiaea, Cortinarius chrysolitus, C. davemallochii and Galerina hybrida) in various raised bogs and transitional mires (61 localities, 144 collections) in a wide area around disturbed, industrially harvested raised bogs under restoration. We aim to verify whether these species could be detected by routine environmental sequencing (eDNA), and to assess their habitat requirements by analysing the vegetation around fruitbodies and fungal communities under them. Generally, the studied fungal indicator species preferred sites where peatland specialist plants occurred. Vegetation survey and eDNA highlighted a broad ecological niche of Galerina hybrida across peatlands and a preference of Cortinarius chrysolitus for transitional mires. Because the eDNA approach sometimes failed to detect these species even under their fruitbodies (14% of samples), and these species tend to occur rarely and patchily in their habitats, we subsequently selected eight co-occurring vascular plant species, four co-occurring bryophyte species and 23 co-occurring fungal OTUs (operational taxonomic units) which were significantly associated with the studied fungal indicator fruitbodies, possibly indicating potentially suitable conditions for them. The information obtained from eDNA of fungi is still difficult to interpret because many unknown OTUs were detected in the datasets. Nevertheless, similarly to the co-occurring plant species, the presence of the co-occurring fungal OTUs was significantly higher in undisturbed raised bogs than in the disturbed ones. This approach may predict the occurrence of fungal indicator species in the absence of their fruitbodies or when environmental sequencing fails to detect their DNA. This method can be applied to more effectively monitor the restoration success in peatlands