| Popis: |
Summary The seasonal dynamics of nitrogen reserve compounds depends not only on the climatic factors but also on the special behaviour of the sweet flag (Acorns calamus L.). It bears green submersed non-growing leaves in winter and leaf extension occurs earlier than that of surrounding plants in spring. Roots, rhizomes and leaves are not of equal importance with respect to nitrogen storage. Because of its high biomass, most nitrogen is stored in the rhizome. Leaves show similar concentrations of nitrogen but the biomass in winter is considerably lower. Roots are storage organs of minor importance, yet they survive winter. These organs differ in the kind of nitrogen compounds they contain. In the rhizome, high amounts of arginine, asparagine and proteins are present in winter. Asparagine is the predominant amino acid in winter leaves. Alanine accumulates in roots when plants are submerged. Concentrations of ammonium are moderate throughout the year in roots (1-2 μmol/g fw). Arginine seems not to be translocated in large amounts out of the rhizome into expanding leaves. Analysis of bleeding sap showed hardly any arginine but elevated concentrations of asparagine and glutamine. With respect to nitrogen cycling strategies, we conclude that A. calamus is a combination of the translocation type and the assimilation type. Nitrogen compounds of senescing leaves are efficiently translocated into rhizomes. Furthermore, ammonium is available throughout the whole year and is used to form amino acids. The significance of these and other facts is discussed with regard to this plants success as a vigorous invader at its site. |
