Abstract

Plant communities rely on the belowground microbial community for nutrient uptake, pathogen resistance, growth and establishment. Although the importance of soil microorganisms has been acknowledged for some time, the soil remains one of the least explored habitats on earth. In this thesis I examine the relationships between the aboveground plant community and three functionally different fungal communities in a boreal mixed-wood forest in Québec. The first group, the ectomycorrhizal fungi, are mutualists with many canopy tree species in the plots. As their host is their main carbon source, the communities of these fungi were significantly correlated with the aboveground tree community. These fungi were analyzed using morphological and DNA-based methods, and comparisons of these two techniques showed that each targeted certain groups of ectomycorrhizal fungi. Therefore, the best method to analyze the communities of these fungi would be a combined assessment based on both of these techniques. The second group was the arbuscular mycorrhizal fungi, which form mutualistic associations with the herbaceous plants in the plots. To target these fungi, Clintonia borealis, a herbaceous plant found in all the plots was sampled. DNA based identification methods showed that one fungal type was dominant, and was similar to one collected from varied environments and hosts from distant geographical locations. The last group, the saprophytic microfungi, is not mutualistic with plants but they are decomposers of dead plant material. Statistical analyses showed that the microfungi were most closely correlated with the understory plant species composition than with the soil chemistry or overstory tree species. Significant correlations between plant communities and each of the fungal communities were found, stressing the importance of analyzing both aboveground and belowground components in a combined approach in order to further enhance our understanding of terrestrial ecosystems.