Response of photosynthetic apparatus of Isochrysis galbana to different nitrogen concentrations

The chlorophyll fluorescence parameters of Isochrysis. galbana at different nitrogen levels were determined by using chlorophyll fluorescence with the aim of better understanding the operative status of photosynthetic system II (PSII) and electron transport chain in oleaginous microalgae. In this experiment, the growth and photosynthetic efficiency were restricted in N-deprived I. galbana, which were mainly presented in significant decrease of cell numbers and chlorophyll content, the dramatic decline of Fv/Fm, P.I., ΦPSII and rETR, and commensurate increase of NPQ and Wk. The growth of algal cells gradually increased with rising nitrogen concentration, especially reached the top in N-1.76 mM L1 medium, but were inhibited in N-3.52 mM L1 medium. The results suggested that N-deprivation and N-deficiency could inhibit the growth and photosynthesis of I. galbana, but excessive nitrogen could also restrict the growth of algal cells. The nitrogen concentration plays an important role in the algal growth and photosynthesis.