Responses of Thalassiosira Pseudonana to different nitrogen conditions

In this paper, the growth rate and photosynthesis of Thalassiosira pseudonana were studied under different nitrogen sources (nitrate, nitrite, ammonium and urea) and nitrogen starvation, in order to provide a basis for elaborating the adaptation mechanism of marine microalgae to the complex and varied nitrogen environment in the coastal area. The results showed that under the condition of nitrogen starvation, the population growth of T. pseudonana was inhibited, the cellular pigments were decomposed, and the photosynthetic efficiency was significantly inhibited. T. pseudonana grew well in all the four nitrogen sources, but showed inhibition in the high ammonium treatment. There was no significant difference in the contents of chlorophyll a, c and the total carotenoids in the algal cells under different nitrogen source conditions during the exponential growth period, while the levels of pigments in the urea treatment group were significantly increased in the end of the platform phase. Different PSII photosynthetic parameters of T. pseudonana did not vary in different treatments, while the parameters were significantly higher in the 880 μmol/L ammonium treatment than in other treatments at the end of the experiment. In conclusion, T. pseudonana could assimilate different nitrogen source for growth but high concentrations, and the changing patterns of population growth and photosynthesis were not consistent under different nitrogen source conditions, suggesting the different photosynthetic performance of T. pseudonana was not the main reason leading to the difference in the population growth.