Seasonal trends in energy contents and storage substances of the Mediterranean species Dittrichia viscosa and Thymelaea tartonraira

Abstract

The annual fluctuations of soluble sugars, lipids, starch and nitrogen content were determined in leaves, stems and roots of Dittrichia viscosa and Thymelaea tartonraira. The energy content of storage substances was calculated. Soluble sugars increased in all parts of both species during the summer while starch and total lipids decreased. The annual variations of lipids, total and protein-nitrogen and the energy content of storage substances differed between the leaves of the two species. In contrast, starch and soluble sugars showed similar annual fluctuations in the leaves of both species. During the periods of growth foliar nitrogen concentration was correlated with foliar soluble sugar and starch concentrations, but relationships varied with time and between species. The differences in leaf lifespan between species affected only the leaf storage contents and not the stem and root contents. A sink storage system may be functioning between stems and roots of both examined species.