EFFECTS OF D IFFERENT N:P RATIOS ON THE GROWTH OF PSEUDO 2N ITZSCH IA PUNGENS, PROROCEN TRUM DONGHA IENSE AND PHAEOCYSTIS GLOBOSA

In natural waters, the growth of phytop lankton was mainly affected by nitrogen, phosphorus and N:P ratios. In this paper, three rep resentative HAB algae isolated from the coastalwaters of China, Prorocentrum donghaiense, Phaeocystis globosa and Pseudonitzschia pungenswere chosen for the research. Effects of different N:P ratios on the growth of these algae were tested in laboratory. This culture was grown in f/2 media at ca124℃ with salinity of ca130, light intensity of ca1.20μE/m2 ·s, and light2dark cycle of 12:12. Nitrogen and phosphorous starved cells of the species were obtained bygrowing the cells in f/2 media without addition of nitrogen and phosphorous until the ambient nitrogen or phosphorous had been dep leted for 3 days1Such cellswere used to test differentN:P ratios on the growth rate of three HAB algae under twoconditions of low-phosphorus (01362μmol/L PO3-42P) and high phosphorus (3612μmol/L PO3-42P), the N:P ratios of 0, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 50:1 and 100:1 were adop ted, respectively1The results showed that the op timum N:P ratios of P1donghaiense, P1 globosa and P1 pungens were 30:1, 30:1 and 10:1 respectively. While N:P ratios below 100:1, the relevancy between growth rate of the algae and nutrients concentration was more significant than that between growth rate and N:P ratios.P1 donghaiense and P1 globosa required high concentrations of nutrients, and growth rates inlow phosphorus conditions were much less than that in high phosphoruswaters; compared with two algae above mentioned, P1 pungens demanded less nutrients, and maintained high growth rate under low phosphorus conditions.