AMMONIUM UPTAKE BY CHONDRUS-CRISPUS STACKHOUSE (GIGARTINALES, RHODOPHYTA) IN CULTURE

Cultivated Chondrus crispus was used in N-NH4 uptake experiments in the laboratory. An elevation of temperature increased the apparent rate of uptake, especially up to 11 °C. Uptake in the dark was found to be 83 % of that in the light. The apparent uptake decreased with increasing internal N pool; rates were 26.5, 22.2 and 20.2 μg N g dry wt-1 min-1 for internal N pools of 2.7, 3.5 and 4.6%, respectively. Apparent uptake increased with the substrate N concentration. The resulting curve has two components: an active uptake and a diffusion component at high (> 5000 μg N L-1) external N levels. Ks and Vmax were calculated by deducting the diffusion component from the uptake curve: these were of 497 μg N L -1 and 14.4 μg N g dry wt-1 min-1. respectively, and reflect a low substrate affinity. This could be the result of 10 years of continuous culture of C. crispus. Uptake was similarly followed in the culture tanks and showed comparable results; nighttime would be the most appropriate time to supply nutrients. © 1990 Kluwer Academic Publishers.