STUDIES ON THE INFLUENCE OF NUTRIENTS ON THE COMPOSITION AND STRUCTURE OF ALGINATE IN LAMINARIA-SACCHARINA (L) LAMOUR (LAMINARIALES, PHAEOPHYCEAE)

Laminaria saccharina (L.) Lamour. (Laminariales, Phaeophyceae) was cultivated in May —July and September— December in tanks supplied with running seawater enriched with 20 ¼M NO- 3 and up to 500 ¼M PO4 -3 The alginate composition and sequential structure were analysed by NMR-spectroscopy. The total guluronate and G-block contents were always higher in the old blades than in the new. In stipes the G-block content was higher in new stipes than in old. In spring the G-block content both for new and old blades was higher in the phosphate-enriched conditions than in the controls, with a simultaneous decrease in the total content of mannuronate. The highest total guluronate (FG = 0.55) and G-block fractions (FGG = 0.43) were observed in old blades in spring. Even though the algae grew in a very sheltered environment, the total guluronate and G-block contents increased with increasing phosphate concentration in the medium. Extra light in autumn resulted in alginates similar to the type found in spring in plants growing in natural kelp beds. Phosphateenrichment of the seawater resulted in a proportional increase in total P in the tissue, while enhanced supply of nutrients did not increase tissue-nitrate and tissue-N in May—July. Elongation growth rates stayed high in late spring as a result of nutrient enrichment (0.5 —0.6cm day-1), but increased nutrient levels did not enhance the winter growth (about 0.1 cm day-1). Both relative age of the algal tissue and the external phosphate concentrations seemed to affect the alginate composition and sequential structure. Copyright © 1990 Walter de Gruyter