Mycorrhizal fungi mediate aboveground – belowground interactions in forest ecosystems

The activities of plants and soil microbes are the primary drivers of forest ecosystem processes such as carbon (C) and nitrogen (N) cycling, and mycorrhizal fungi serve as a bridge between these two groups of organisms. The combined efforts of trees and associated mycorrhizal fungi to seek soil nutrients links C and N cycling through effects on saprotrophic communities and decomposition activity. In these studies, I investigated the effects of arbuscular (AM) and ectomycorrhizal (EcM) associations on microbial communities and ecosystem processes related to SOM decomposition and N cycling, and in turn how differences in soils beneath AM and EcM associated forests affect seedling regeneration. In the first study, I aimed to address the relative contributions of aboveground-belowground traits in tree-mycorrhizal associations to differences in microbial communities and decomposition activity. Next, I examined how mycorrhizal fungi mediate the effects of inorganic N availability on seedling rhizodeposition, which is the combined addition of fine roots, mycorrhizal hyphae, and exudates to the soil organic matter pool. Finally, I addressed how differences in soil beneath AM and EcM-associated forests affected seedling regeneration following timber harvesting, a human-caused forest disturbance. The combined results from these studies suggest that as mycorrhizal dominance shifts with changes in forest community composition, so will belowground carbon investment and nitrogen availability, with subsequent effects on saprotrophic communities and decomposition. Consequently, including tree-mycorrhizal associations is essential when researching drivers of soil biogeochemical cycles and forest regeneration, as belowground effects are equally if not more important than aboveground effects in shaping forest ecosystem processes