COS 24-5 - Somewhere, some incredible fungus is waiting to be known: Biogeography and ecology of unknown fungi

Background/Question/Methods

Fungal communities contribute to global ecosystem processes such as nutrient cycling, interact with plants, and regulate global primary productivity. Even with our understanding of the importance of fungi, we are still only beginning to capture the richness of this kingdom with global estimates ranging from 1.5 to 13 million species and < 7% of species described. Furthermore, little is known about the location, both geographic and biological, of hot spots of unclassified fungal species. Recent meta-analyses have found that plants and lichen are hotspots of unknown taxa, but soils host the highest relative abundance. Here we asked 1) what global regions host the highest portions of unknown fungi?, 2) how does the biogeography of unknown fungi vary between substrate types?, and 3) how does the breadth of interactions with host species vary between known and unknown fungi? We used the meta-analysis of ITS2 metabarcoding studies within the GlobalFungi database to explore these global unknown taxa. Sequence variants were extracted from studies and clustered into OTUs based on 97% sequence similarity. OTUs were then classified into known and unknown taxa based on similarity to the reference sequences in the UNITE database.

Results/Conclusions

Most studies in the GlobalFungi database were from Europe (46.4%), North America (19.5%), and Asia (15.2%). Unknown taxa were widespread in the database making up 46.1% of reads and 69.3% of OTUs. Across all sample substrates, the proportion of reads and OTUs from known species increased with increasing latitude. This positive correlation was driven by fungi found in soil and deadwood samples while root substrates had only a weak positive correlation with latitude. Furthermore, the proportion of reads from known taxa in shoots showed a weak negative correlation with latitude. This result suggests that similar to many macro-organisms, the tropics are a hotspot of yet to be classified fungi, with the possible exception of shoot associated taxa. Known taxa interacted with a larger percentage of the host plant species richness surveyed in the database (2.52% to 3.49% of plant species, root and shoots) than unknown taxa (1.84% to 2.58% of plant species, roots and shoots). This result suggests that unknown taxa may be more specialized in host interactions than known taxa. Unknown taxa are likely an important portion of the pool of global fungi with hotspots in lower latitudes and more specialized interactions with plant hosts.