The relative growth rate, allocation of biomass into leaves, pseudostems, roots and rhizomes, specific leaf area, net photosynthesis and respiration were measured in young plants of a perennial grass Calamagrostis epigejos growing in a substrate with a different amount of nitrate ions as the sole source of nitrogen. Both the metabolic and the morphogenetic processes were strongly influenced by varying nitrogen availability. The high relative growth rate of C. epigejos observed in fertile sites rich in mineral nitrogen is, therefore, caused not only by the better photosynthetic performance of leaves, but also by the more advantageous allocation of new biomass within a plant.