This study assesses the growth and morphological responses, nitrogen uptake and nutrient allocation in four aquatic macrophytes when supplied with different inorganic nitrogen treatments (1) NH 4 +, (2) NO 3 -, or (3) both NH 4 + and NO 3 -. Two free-floating species (Salvinia cucullata Roxb. ex Bory and Ipomoea aquatica Forssk.) and two emergent species (Cyperus involucratus Rottb. and Vetiveria zizanioides (L.) Nash ex Small) were grown with these N treatments at equimolar concentrations (500μM). Overall, the plants responded well to NH 4 +. Growth as RGR was highest in S. cucullata (0.12±0.003d -1) followed by I. aquatica (0.035±0.002d -1), C. involucratus (0.03±0.002d -1) and V. zizanioides (0.02±0.003d -1). The NH 4 + uptake rate was significantly higher than the NO 3 - uptake rate. The free-floating species had higher nitrogen uptake rates than the emergent species. The N-uptake rate differed between plant species and seemed to be correlated to growth rate. All species had a high NO 3 - uptake rate when supplied with only NO 3 -. It seems that the NO 3 - transporters in the plasma membrane of the root cells and nitrate reductase activity were induced by external NO 3 -. Tissue mineral contents varied with species and tissue, but differences between treatments were generally small. We conclude, that the free-floating S. cucullata and I. aquatica are good candidate species for use in constructed wetland systems to remove N from polluted water. The rooted emergent plants can be used in subsurface flow constructed wetland systems as they grow well on any form of nitrogen and as they can develop a deep and dense root system. © 2011 Elsevier B.V..