| Abstract: | Uptake and assimilation of nitrogen and phosphorus were studied in Olisthodiscus luteus Carter. A diel periodicity in nitrate reductase activity was observed in log and stationary phase cultures; there was a 10-fold difference in magnitude between maximum and minimum rates, but other cellular features such as chlorophyll a, carbon, nitrogen, C:N ratio (atoms) · cell?1 were less variable. Ks values (~2 μM) for uptake of nitrate-N and ammonium-N were observed. Phosphorus assimilated · cell?1· day?1 varied with declining external phosphorus concentrations; growth rates <0.5 divisions · day?1 were common at <0.5 μM PO4-P. Phosphate uptake rates (Ks= 1.0–1.98 μM) varied with culture age and showed multiphasic kinetic features. Alkaline phosphatase activity was not detected. Comparisons of the nutrient dynamics of O. luteus to other phytoplankton species and the ecological implications as related to the phytoplankton community of Narragansett Bay (Rhode Island) are discussed. |
