How to best detect threatened deadwood fungi – Comparing metabarcoding and fruit body surveys

Effective conservation strategies are needed to prevent further loss of biodiversity. This requires a comprehensive assessment of species' presence, distribution, and population sizes. Such assessments can be extremely challenging for species-rich taxa, like fungi, which are difficult to detect and identify. In recent years, metabarcoding applied to environmental samples has proven to be a promising method for fungal detection. However, its potential against traditional fruit body surveys in monitoring threatened fungal species has rarely been tested. Here, we utilized data on deadwood-inhabiting fungi from 569 deadwood objects across five sites in Central Europe to compare the effectiveness of fruit body surveys and metabarcoding (of low and high sampling intensity) in detecting threatened species. Across objects, sites, and per object, metabarcoding was more effective in detecting threatened species than fruit body surveys, regardless of sampling intensity. Eleven percent of all threatened species across all objects and sites could be detected by both methods, 70 % exclusively by metabarcoding and 18 % exclusively by fruit body surveys. The number of species detected by both methods on the same object was <4 %. Effects of high sampling intensity metabarcoding were stronger than low sampling intensity at object level. The effectiveness of the survey method was mainly independent of deadwood object characteristics. We suggest that metabarcoding is a valuable tool for threatened fungal species monitoring and conservation status assessments. However, for a comprehensive assessment, fruit body surveys are still needed, as this method detected a unique set of species and indicates the presence of vital fungal individuals.