Nothing is known about nutrient fluxes along the roots of floating and submerged macrophytes that may be used for removing nutrients from eutrophicated water systems. We have used ion-sensitive microelectrodes to measure fluxes of NH4+, NO3- and H+ along the root apices. One floating (Azolla spp.) and three submerged plant species (Vallisneria natans Lour. Hara; Bacopa monnieri L. Pennell; and Ludwigia repens J.R. Forst) were tested.Ion fluxes showed a specific pattern linked to root zones in all four species. The highest influx of all three ions was found in the meristem zone of B. monnieri, V natans and L. repens. B. monnieri had the greatest capacity to acidify the surrounding medium. In the four species studied, there was a consistent negative relationship between the fluxes of NO3- and H+ measured simultaneously along the root and a positive relationship between H+ and NH4+ fluxes. When NH4+ and NO3- were both present in the bathing medium, the meristem zone had the largest capacity for net NH4+ uptake, whereas the elongation zone showed the highest net NO3- uptake. In the short-term experiments, Azolla spp. had preference for NO3- uptake when NO3- was supplied as a sole source of nitrogen, whereas L. repens required both nitrogen forms in the medium for net nitrogen uptake. When NO3- and NH4+ fluxes were summed, L. repens had the largest and V repens the smallest nitrogen accumulation capacity.Therefore, for industrial purposes, when plants are used for removing N from eutrophicated water, plants species should be selected according to their preferences for different N forms. (c) 2007 Elsevier Ireland Ltd. All rights reserved.