||Forests represent the primary source of volatile organic compounds (VOCs) globally, and VOCs significantly impact ecological and atmospheric processes, including the production of ozone. Most of what is known about VOC production in forests comes from studies of live canopy foliage. However, recent work indicates that roots and soil microbes can be considerable sources of VOCs, with implications for models of atmospheric chemistry and ecosystem carbon budgets. In this project, soil and canopy VOC fluxes will be quantified in situ in forests dominated by different tree species. The mycorrhizal fungi associated with tree roots differ in their response to environmental variability and their effects on soil organic matter decomposition, with likely consequences for soil VOC emissions. In addition, we will partition soil emissions into autotrophic (i.e. root and mycorrhizal-derived) versus heterotrophic sources and determine underlying biological mechanisms controlling emission dynamics. Driven by our knowledge of plant-fungal dynamics, microclimate, VOC emission and transport rates, and atmospheric hydroxyl radical (OH) concentrations, we will improve ecosystem models and assess the potential for soil VOC emissions to influence ozone production. By understanding the important links between environmental variation, plant species composition, and the underlying mechanisms controlling soil VOC fluxes, we will be able to make predictions as to how future changes in regional stand types, land use, and climate will impact atmospheric chemistry, air quality, and ecosystem function. Thus, the results from this project will contribute a comprehensive mechanistic understanding of biological and physical controls over VOC emissions from the molecular-to-ecosystem-to-atmospheric scales and improve the predictive capabilities of land surface models and global carbon cycling.