Many plants are dependent on belowground fungi to help them obtain nutrients and respond to environmental stress. Revealing the patterns and drivers of these interactions is important for understanding forest ecology and improving management practices. Plant-fungal associations in the soil can dramatically influence plant growth and terrestrial ecosystem function. This research will take the advantage of several existing datasets, including those collected by National Ecological Observatory Network (NEON) and the U.S. Forest Service (USFS), to understand: 1) nation-wide patterns of plant-fungal associations; 2) key factors that influence these associations; and 3) how plant-fungal interactions influence key ecosystem functions such as carbon cycling. This research project will contribute to the fields of microbial ecology, ecosystem science, and global change biology by formulating and testing new theories about plant-fungal associations. Results of the project will inform forest managers, policymakers, and other stakeholders on how to improve ecosystem management of plant and fungal biodiversity to promote sustainable ecosystems. The project will contribute to the professional development of diverse students at several stages.<br/><br/>The goal of this project is to understand the patterns, drivers, and consequences of the linkages between plant and mycorrhizal fungal diversity across spatial and temporal scales. This information will enable better predictive understanding of essential ecosystem functions which they control. The project will use a holistic, scale-dependent framework that forecasts the strength and direction of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal-plant associations, and provides greater insight about the consequences for ecosystem functioning across space and over time. Specific objectives of the project include: 1) elucidation of patterns of plant and mycorrhizal fungal diversity across scales by extensive DNA sequencing and analysis; 2) determination of key abiotic and biotic drivers of observed co-occurence patterns; and (3) forecasting the effects of plant-mycorrhizal fungal couplings on tree productivity and soil C storage, two key forest ecosystem functions. By linking multiple facets of both above- and belowground diversity in a scale-dependent context, the project will produce robust continental-wide distribution maps of AM and EM fungi for the first time. Leveraging data-rich sampling of putative biotic and abiotic drivers of plant and fungal diversity by NEON and the USFS, the project will also provide broad-scale understanding of when and where these drivers serve to couple or decouple plant and mycorrhizal fungal diversity. Finally, by linking plant and mycorrhizal fungal diversity to the consequences they have for plant productivity and soil C storage and stability, the project will improve understanding of ecosystem resilience to environmental stress. The project will train diverse undergraduate and graduate students, postdoctoral scholars, and will enhance the development of three early=career scientists.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.