Seasonal Dynamics of Nitrogenous Compounds in a Nitrophilic Weed I. Changes in Inorganic and Organic Nitrogen Fractions of the Different Plant Parts of Urtica dioica

The seasonal dynamics of nitrogenous compounds in the differentplant parts of Urtica diocia, a perennial nitrophilic weed,were investigated under natural conditions during the courseof a year. In the below ground plant parts (roots and rhizomes)a nitrogen store was built up during summer and autumn, consistingmainly of free amino acids. In the seeds, however, proteinswere of major importance as nitrogen reserve. In early springthe below ground nitrogen store was quickly mobilized, translocatedto the upper plant parts and used for the protein synthesisof the shoots, enabling them a rapid growth prior to the developmentof their own capacity for nitrogen assimilation. (Received September 3, 1984; Accepted November 2, 1984)