he rhizosphere or plant root zone is an area of intense microbial and enzymatic activity and many symbioses form that are critical to plant health and crop productivity. Species-specific plant root exudates (organic acids, hormones, secondary metabolites) signal and encourage growth of a specific prokaryotic and eukaryotic microbial community that is important not only to the plant but also to overall ecosystem health. Seemingly subtle changes in the community induced by ENP exposure could have far reaching implications, including alterations on nutrient uptake, disease suppression, and plant development, as well as the fate of ENPs. For example, Priester et al. (2012) demonstrated that although NP CeO2 had modest effects on soybean health, rates of nitrogen fixation were dramatically reduced and levels of nitrogen fixing bacteria within root nodules on the legume were significantly lower. Given the importance of many of these plant-microbe processes as broad ecosystem services (i.e., nitrogen fixation), studies thoroughly characterizing ENP effects on this area of the plant–soil interface are of critical importance.