[Nitrogen and phosphorus absorption and growth characteristics of Alexandrium tamarense]

The uptake of nitrate and phosphate by Alexandrium tamarense and its growth characteristics were studied in laboratory cultures, which were conducted using environmentally realistic levels of physical factors during red tide occurrences. The results indicated that the specific growth rate had little difference under three nitrate levels (low-nitrate, 0.0882 mmol.L-1; middle-nitrate, 0.882 mmol.L-1; high-nitrate, 2.646 mmol.L-1). The cell yield was the lowest at low-nitrate, a maximum yield was achieved at the middle-nitrate, which increased by 44.7% and 53.6% respectively, compared with high-nitrate and low-nitrate. The cell yield increased with increasing phosphate concentrations in cultures (low-phosphate, 0.0036 mmol.L-1; middle-phosphate, 0.036 mmol.L-1; high-phosphate, 0.108 mmol.L-1), and the maximum yield (17200 cell.ml-1) was observed at high-phosphate concentration, while the maximum specific growth rate occurred at middle-phosphate. The growth conditions had a significant effect on the uptake rate of nitrate and phosphate by cells, and the cells grown in low-nitrate and low-phosphate cultures had a higher uptake rate. Further experiment suggested that lower ratio of N/P promoted the propagation of cells, and the supplementation of nitrate at later exponential growth phase had a positive effect to the accumulation of biomass.