Plastic adjustments in response to P availability were investigated for a freshwater, submerged plant, Ranunculus peltatus Schrank at various stages in its life cycle. A series of three, nine-day-experiments was performed under controlled conditions in April, June and August. R. peltatus plasticity was tested in response to three phosphorus water concentrations (50, 100, 300 lg/l PO4 3––P) and was evaluated using eight morphological and ecophysiological traits related to plant nutrient uptake and use. Some plastic adjustments in R. peltatus were found to be significant mostly for the April experiment. R. peltatus displayed higher nutrient uptake and lower NUE when P availability was high. It tended also to adapt its P uptake rate, which decreased during the experiment. When P availability was low, reverse results were found in the four ecophysiological traits. No morphological plastic adjustments in response to P enrichment were identified in R. peltatus concerning branching or creation of roots. However, the production of sexual organs tended to be enhanced by low P concentrations in the water. Ecophysiological rather than morphological adjustments were highlighted in R. peltatus with respect to P availability. Plasticity was found to depend strongly on the particular phenological stage. These results may constitute valuable information concerning the evaluation and ecological significance of plasticity in freshwater plants