Biomass and Nitrogen Partitioning in a Perennial and an Annual Nitrophilic Species of Urtica

Abstract

Summary Urtica dioica L. and Urtica urens L. are characteristic representatives of nitrophilic weeds. Urtica dioica is a perennial herb, the propagation of which takes place predominantly by rhizomes but to some extent also by seeds. Urtica urens is an annual plant which reproduces exclusively by seeds. The distribution of biomass and of nitrogenous compounds in these two species cultivated under natural growth conditions was investigated. A greater proportion of biomass of the perennial Urtica dioica was found in the root fraction than was the case with the annual Urtica urens , as is documented by the root : shoot biomass ratio of 3.4 and 19, respectively. The distribution of total nitrogen followed in general the trends of biomass partitioning. However, nitrate and free amino acids — in particular the nitrogen-rich asparagine and arginine - were present at the highest concentrations in the parts of the plant mainly contributing to propagation. Both nettles belong to that group of plants, in which nitrate reduction occurs almost exclusively in the leaves. Whereas nitrate was equally distributed between leaves and stalks of Urtica urens , in Urtica dioica the proportion of nitrate in the stalks was eight times higher than in the leaves.