Abstract: The response of Prorocentrum donghaiense and Thalassiosira weissflogii pigments under nitrate (N) and phosphate (P) limitation were studied using HPLC and in vivo fluorescence protocols in batch cultures. For P. donghaiense, the pigment ratio was kept stable under different nutrient conditions from the results of HPLC. For T. weissflogii, there was a lower ratio of chlorophyllide to Chl a during the exponential phase, but the reverse during the stationary phase. Different members of the phytoplankton had different pigments response mechanisms under nutrient limitation. From the results of in vivo fluorescence, the ratio of peridinin to Chl a for P. donghaiense increased in nutrient-free culture, while it was kept stable for nutrient-limited cultures during the exponential phase. For T. weissflogii, the ratio of fucoxanthin to Chl a for each culture increased during the exponential phase, but the ratio under N limitation was apparently lower than that for P limitation during the stationary phase. The results indicate that both pigment ratios from HPLC and in vivo fluorescence of T. weissflogii were changed greatly under different nutrient conditions, which suggests that both ratios could be used as indicators of algal physiological status in different nutrient conditions.

Key words: HPLC, in vivo fluorescence, nutrient limitation, pigments, Prorocentrum donghaiense, Thalassiosira weissflogii.