Forested ecosystems are comprised of tremendous biological diversity and functional complexity both above and belowground. Soil ecosystems are known to contain thousands of species, with many more that have not yet been identified. Soil heterotrophic organisms depend on green plants for their energy, while autotrophs depend on soil hetertrophs for processing and cycling nutrients that are needed for continued growth. Together, heterotrophs and autotrophs form a complex web of interacting entitites, the balance of which is always changing as ecosystems change in response to stress. Our relative lack of understanding about ecosystem processes in general and soil ecosystems in specific makes it difficult to understand how O3 may be affecting forested ecosystems. Ecosystem fluxes of carbon and nitrogen are highly regulated by coupled processes occurring above and belowground. Microbial interactions belowground have been shown to contribute to plant biodiversity and productivity (van der heijden, et al., 1998). Belowground processes also contribute substantially to fluxes of carbon into and out of ecosystems (Law et al., 1999). A better understanding of mechanistic processes occurring in plant roots and subsequent changes in food web organisms is a necessary foundation for understanding how a stress such as O3 affects ecosystem structure and function.