Two geographically distinct populations of the submerged aquatic macrophyte Ceratophyllum demersum L. were compared after acclimation to five different nitrogen concentrations (0.005, 0.02, 0.05, 0.1 and 0.2 mM N) in a common garden setup. The two populations were an apparent invasive population from New Zealand (NZ) and a noninvasive population from Denmark (DK). The populations were compared with a focus on both morphological and physiological traits. The NZ population had higher relative growth rates (RGRs) and photosynthesis rates (P max) (range: RGR, 0.06–0.08 per day; P max , 200–395 mmol O 2 g –1 dry mass (DM) h –1) compared with the Danish population (range: RGR, 0.02–0.05 per day; P max , 88–169 mmol O 2 g –1 DM h –1). The larger, faster-growing NZ population also showed higher plasticity than the DK population in response to nitrogen in traits important for growth. Hence, the observed differences in growth behaviour between the two populations are a result of genetic differences and differences in their level of plasticity. Here, we show that two populations of the same species from similar climates but different geographical areas can differ in several ecophysiological traits after growth in a common garden setup.