The responses of dwarf black mangroves (Avicennia germinans) and components of the microbial community to the addition of nitrate over a 2-year period were examined. The field study was conducted in the Indian River Lagoon (Florida) in a mangrove-dominated impoundment that was established for purposes of mosquito control. The responses of mangroves to the regular addition of nitrate were insignificant or relatively minor compared to responses of the components of the microbial community. Denitrification rates, measured in the field and laboratory, increased significantly in fertilized plots and nitrous oxide emission rates were almost six times higher in fertilized plots. Nitrogen fixation was significantly lower in fertilized plots. Results suggest that mangrove systems in the N-limited Indian River Lagoon are likely to be long-term sinks for any increases in N loading.
