Effect of Ammonium and Nitrate Supply on Dry Matter Production and Nitrogen Distribution in Urtica dioica

Abstract

Summary The influence of low (3 mM) and high (22 mM) nitrate or ammonium supply on biomass and nitrogen distribution of Urtica dioica L. was studied under controlled environmental conditions. With respect to biomass production growth on nitrate was more effective than on ammonium irrespective of the concentration of the nitrogen source. Low nitrogen supply favoured dry matter formation of the root plus rhizome fraction, whereas high nitrogen supply resulted in a preferential growth of the leaf plus stalk fraction. Growth on 22 mM nitrate or ammonium caused a significant higher content of total nitrogen, nitrate and free amino acids (particularly asparagine and arginine) in all plant parts as compared to that found in plants grown on the 3 mM nitrogen sources. The distribution of total nitrogen between the various plant parts was similarly affected by the concentration of the nitrogen supply as was that of biomass. The main nitrogen storage compounds were nitrate on the one hand and the free amino acids on the other when nitrate or ammonium were the nitrogen sources. Nitrate was preferentially accumulated in the leaves and the stalks, whereas the free amino acids were more equally distributed between leaves, stalks and roots; however, their concentrations were significantly highest in the stalks, if ammonium was the nitrogen source.