The function of ectomycorrhizal fungi in regenerating and mature forests

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Ectomycorrhizal (EM) fungi are root symbionts that account for approximately 30% of microbial biomass in boreal forest soils and mediate throughput of 60% of soil carbon. EM fungi have been studied primarily with respect to their role in modifying host growth by increasing nutrient supply but, increasingly, their potential role in nutrient cycling is also being appreciated. Following stand-destroying disturbances, such as wildfire or clearcut logging, EM fungi that colonize seedlings in regenerating stands are different from those that colonize seedlings in the original forest. I propose to continue to use recent clearcuts as a model system to answer fundamental questions about how EM fungal communities re-establish after disturbance. We will examine whether EM fungi that colonize young seedlings in clearcuts differ physiologically, or have different mechanisms of dispersal, than fungi that colonize seedlings in forests. Specifically, we will use stable isotope approaches to study the uptake of nitrogen and its translocation to seedlings by EM fungi, as well as the relative demands of these two groups of fungi for fixed carbon from their host plants. In addition, we will quantify the relative importance of (i) aerial spores, (ii) persistent propagule banks and (iii) root-to-root hyphal spread as sources of inocula in montane spruce/pine forests and clearcuts. A fascinating recent discovery about EM fungi is that a single fungal individual can concurrently colonize root systems of several neighbouring trees. While studies have investigated how these mycelial networks influence belowground transfer of carbon and nutrients from one tree to the other, we will take a fungus-centered approach to ask what factors influence the distribution of minerals nutrients by the fungus to each host. We will use stable isotopes and quantum dots (fluorescent nano-particles) as tracers for these nutrients in microcosms in the lab. Both these lines of research will increase our understanding how EM fungi, which are ubiquitous in Canadian mixed and coniferous forests, influence ecosystem services and plant nutrition, as well as how forest management may affect those services. Ten undergraduate and five graduate students will be trained.