NUTRITIONAL STUDIES OF THE SUBMERGED MARINE ANGIOSPERM THALASSIA TESTUDINUM I. GROWTH RESPONSES OF AXENIC SEEDLINGS TO NITROGEN ENRICHMENT

Algae- and bacteria-free seedling cultures of the seagrass Thalassia testudinwn Banks ex König were utilized to evaluate effects of nutrient enrichment on growth and chemical composition. Seedlings cultured in media based on both synthetic seawater and NH-15 medium amended with inorganic nitrogen (NH₄⁺) and organic nitrogen (glutamine, glutamate, urea and yeast extract) exhibited no growth enhancement relative to controls in the growth parameters measured. General decreases in green leaf areas and leaf widths after one month coupled with relatively high C:N ratios after 3 months in culture suggest utilization and depletion of stored reserves with little or no assimilation of exogenous nutrients. These observations coupled with previous results in non-axenic seedling cultures indicate microbial associations may play a critical role in the nutrient physiology of this species.