Arbuscular mycorrhizal fungal diversity and association networks in African tropical rainforest trees

Abstract

Tropical rainforests represent one of the most diverse and productive ecosystems on Earth. High productivity is sustained by efficient and rapid cycling of nutrients through decomposing organic matter, which is for a large part made possible by symbiotic associations between plants and mycorrhizal fungi. In this association, an individual plant typically associates simultaneously with multiple fungi and the fungus associates with multiple plants, creating complex networks between fungi and plants. However, there are still very few studies that have investigated mycorrhizal fungal composition and diversity in tropical rainforest trees, particularly in Africa, and assessed the structure of the network of associations between fungi and rainforest trees. In this study, we collected root and rhizosphere soil samples from Ise Forest Reserve (Southwest Nigeria), and employed a metabarcoding approach to identify the dominant arbuscular mycorrhizal (AM) fungal taxa associating with ten co-occurring tree species and to assess variation in AM communities. Network analysis was used to elucidate the architecture of the network of associations between fungi and tree species. A total of 194 AM fungal Operational Taxonomic Units (OTUs) belonging to six families were identified, with 68% of all OTUs belonging to Glomeraceae. While AM fungal diversity did not differ between tree species, AM fungal community composition did. Network analyses showed that the network of associations was not significantly nested and showed a relatively low level of specialization (H2= 0.43) and modularity (M= 0.44). We conclude that, although there were some differences in AM fungal community composition, the studied tree species associate with a large number of AM fungi. Similarly, most AM fungi had a large host breadth and connected most tree species to each other, thereby potentially working as interaction network hubs.Graphical Abstract