| The contents of cellular chlorophyll a (Chl-a), chlorophyll c (Chl-c), total coloured carotenoids (TCC) and the photosynthesis of Skeletonema costatum and Prorocentrum donghaiense under different nutrient conditions were studied. The results showed that both species in the low nutrient concentration conditions had lower cellular Chl-a, Chl-c and TCC content than those in the high nutrient concentration conditions. When the initial N/P ratio was 16/1 while the concentrations were different, the two species had different photosynthetic rate responses. For S. costatum, the photosynthetic rate normalized by cell in the low nutrient concentration group (64 μmol/L N and 4 μmol/L P) was significantly lower than that in the high concentration group (256 μmol/L N and 16 μmol/L P) from the fifth day, and at the end of the experiment (on the seventh day), the photosynthetic rate was 0.031×10-4 μmol·(cell·h)-1 and 0.13×10-4 μmol·(cell·h)-1 respectively, while the photosynthetic rate normalized by Chl-a was 12.92 μmol·(μg·h)-1 and 13.03 μmol·(μg·h)-1 for the two groups respectively, and there was no significant difference between them; however, for P. donghaiense, the photosynthetic rates normalized by both cell and Chl-a in the low concentration conditions (64 μmol/L N and 4 μmol/L P) were significantly higher than those in the high concentration conditions (256 μmol/L N and 16 μmol/L P). For the two species, when P was sufficient, the low N concentration group (64 μmol/L N and 36 μmol/L P) and when N was sufficient, the low P concentration group (883 μmol/L N and 4 μmol/L P) had higher photosynthetic rates normalized by both cell and Chl-a than the high N concentration group (256 μmol/L N and 36 μmol/L P) and the high P concentration group (883 μmol/L N and 16 μmol/L P) respectively. There was a significant positive relationship between the photosynthetic rate and the intracellular P for both species, and P. donghaiense had higher cellular photopigment contents and photosynthetic rates than S. costatum under the same nutrient conditions. It could be inferred from their photosynthetic characteristics that P. donghaiense would survive better in low nutrient conditions compared with S. costatum. |
