Structure and function of mycorrhizal networks in North American forests

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The overall objective of my team's research program is to explore the structure and function of mycorrhizal networks in North American forests. A mycorrhiza is a mutualistic symbiotic association between fungi and plant roots. Ectomycorrhizas (ECM) are formed on many economically important forest trees including members of the pine family, whereas ericoid mycorrhizas (ERM) are found on members of the plant family Ericaceae (eg., huckleberry). A mycorrhizal network (MN) occurs when roots of two or more plants associate with the same fungal mycelium. Linkage into an MN can improve the survival and productivity of newly established seedlings, which adds to the resilience of forests. Most mycorrhizal network studies have focussed on ECM or arbuscular mycorrhizal networks, whereas little is known about ERM networks. The short-term objectives of my program are to determine: 1) the average life-span of genotypes formed by two network-forming ECM fungal species; 2) whether ERM form extensive and potentially functional networks; and 3) the ability of ERM fungi to break down soil organic carbon and recycle nutrients under varying environmental conditions. For Objective 1, my team will identify genotypes over a three-year period from samples taken within metres of those sampled in the first year. To obtain an idea of longer-term turnover, we will compare genotypes identified in the first three years with those collected 5-12 years ago. If networks last for multiple years, this suggests that benefits of the network could compound from one year to the next. For Objective 2, my team will collect data relating to anecdotal observations that Vaccinium species grow larger when located close to large conifer trees. In addition, we will test the hypothesis that two mycorrhizal hosts (spruce and huckleberry) form MNs with each other. We will map and quantify huckleberry/spruce distributions, identify the fungi that are common to both spruce and huckleberry roots, and grow them in tripartite symbioses in the lab. This information will be valuable for the rehabilitation of two areas that are vulnerable to anthropomorphic disturbances: the subalpine and boreal forests. For Objective 3, to investigate saprotrophic abilities of an ERM fungus we will select genes coding for carbohydrate and plant cell wall-degrading enzymes. We will use information from 3 recently generated transcriptomes to do this. We will quantify the expression of these genes and compare them when the fungi are free living vs. in symbiosis, among varying substrate complexities, and among varying levels of carbon supply to the fungus from the plant symbiont. This information will provide valuable information to climate change models estimating carbon dioxide release into the atmosphere. In total, this program will train 14 HQP (2 MSc., 3 Ph.D., and 9 undergraduate students).**