Ectomycorrhizal fungi are ubiquitous symbionts of forest trees. Tree and fungus engage in a mutualistic symbiosis where fungal mycelium grows around fine roots of the tree and both partners engage in a reciprocal exchange of nutrients – carbon (in the form of sugars) from the plant to the fungus, and nitrogen and phosphorous from the fungus to the plant. Besides supporting each other with nutrients, ectomycorrhizal symbiosis has also been shown to improve drought tolerance of trees and new seedling establishment. Ectomycorrhizal fungi, who form a recalcitrant mycelium in lower soil horizons, also contribute to capturing photosynthetically derived carbon in the soil. Consequently, ectomycorrhizal fungi have the potential to be important players in mediating global change, by improving resistance to drought, one of the extreme weather events projected to increase and already threatening survival of forests worldwide, as well as by acting as carbon sinks. Ectomycorrhizal symbiosis has evolved repeatedly and independently. Many ectomycorrhizal fungi are thought to be generalists but our understanding of the functional diversity of different ectomycorrhizal fungal species remains limited, especially at finer-scale resolution. The aim of this project was to improve our understanding of how closely-related generalist ectomycorrhizal species differ in interacting with a specific tree genotype. In particular, we wanted to know how these differences are mediated by nutrient availability (signifying a universally recognizable language) as opposed to elements of the plant immune system (more reflective of a fine-tuned, evolved response to specific interaction partners). A better understanding of how species-independent and species-specific processes influence the establishment of ectomycorrhizae and the phenotypic impact on the plant will be important not only for forest management but also to guide efforts in fungal conservation.
