Multiple Nitrogen Utilization Strategies and Phytoplankton Species diversity: Nitrate Assimilation in N2-fixing Bloom-Forming cyanobacteria

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Excessive nitrogen (N) loading supports eutrophication in many aquatic ecosystems. This study will assess the nutritional physiology and ecological role of nitrogen-fixing cyanobacteria, an algal group implicated in the eutrophication process. These cyanobacteria support their N needs by fixing atmospheric di-nitrogen (N2); however some species can also utilize nitrate, a dissolved form of combined nitrogen. Whether invasive N-fixing cyanobacteria successfully compete with native species in systems experiencing increased nitrate loading may depend on species-specific ecological trade-offs between nitrate and N2 utilization. To test this hypothesis, the roles of N uptake and utilization mechanisms potentially promoting dominance of the invasive and toxic Cylindrospermopsis raciborskii over native Anabaena spp. in Florida lakes, will be investigated. In-situ field manipulations and culture-based studies will be used.This study will improve the ecological theory on which the regulation and management of phytoplankton communities is based. Because of the complexity of their nutritional physiology, N2-fixing cyanobacteria are problematic when managing water quality. This study will provide valuable information to managers developing nutrient reduction strategies to control eutrophication in systems with nuisance (e.g. toxic) cyanobacteria. Additionally, toxic cyanobacterial blooms are undesirable in waters used for drinking and recreation. The impacts of toxic cyanobacteria can ultimately be felt up the food chain, including humans. Graduate students will play an integral role in the research, and undergraduates in the Carolina Environmental Program will utilize the project in coursework and participate in the research through independent study.