Mycorrhizal or not mycorrhizal? Assessing the role of root-associated fungi in plant nutrition

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In nature, plant roots associate with complex microbial communities that determine plant health and productivity. These communities are rife with fungi adapted to colonize roots, which develop a range of pathogenic to mutualistic interactions with plants. Mycorrhizas are widespread, stable root-fungus associations, in which the fungus assists the plant in acquiring nutrients and water and receives photosynthates in return. However, the large majority of root-associated fungi have unknown functions and cryptic effects on plant fitness, which raises questions about how these symbioses evolved and are maintained. It is hypothesized that these non-mycorrhizal fungi provide hosts with benefits in exchange for plant resources, or that they help to maintain root microbial communities. Indeed, recent research shows that non-mycorrhizal fungi can benefit plants in multiple ways, including the assistance in plant nutrients' uptake in a mycorrhiza-like manner. The generality of these interactions, however, remains to be tested. The project proposed here aims at a systematic assessment of the potential of non-mycorrhizal root-associated fungi in assisting plants' nutrition. The project will target functionally relevant groups of root-associated fungi by performing fungal diversity samplings across natural gradients of nutrient availability, and by using in vitro enrichment trials to detect and isolate these fungi. The involvement of selected fungal groups in plant nutrition will be directly determined by using plant-fungus co-cultivation bioassays, in which nutrient translocation will be detected by means of tracer isotopes. Phylogenetic and trait-based analyses will be used to explore patterns of functional traits occurrence across fungal lineages, in order to propose hypotheses about the forces driving the evolution of the root-symbiotic lifestyle in fungi. Deciphering the cryptic ecology of root-associated fungi will further our understanding on how plant-microbiome functions depend on individual microorganisms and food webs, and will contribute to the development of methods for the application of fungi in sustainable agriculture.