Morphology, growth, biochemical composition and photosynthetic performance of Chlorella vulgaris (Trebouxiophyceae) under low and high nitrogen supplies

Storage triacylglycerol accumulated by oleaginous microalgae have been utilized as optimal feedstock for biodiesel production. Nitrogen limitation is one of the most effective approaches in inducing oil accumulation in microalgae. However, the mechanism underlying this process is not well established. The aim of the present study was to determine changes in morphology, growth, biochemical composition, and photosynthetic performance of Chlorella vulgaris JNU13 under low nitrogen supply (LN, 3.5 mM) and high nitrogen supply (HN, 17.6 mM). The results showed that LN repressed cell division and cell weight gain. C. vulgaris under HN showed higher lipid levels compared to those subjected to LN. LN showed a decrease in photosynthetic capacity [relative electron transport rate (rETR), photosynthetic oxygen evolution rate (Pn), and utilization efficiency of light energy (α)], ratio of PS I to PS II, dark respiration rate (Rd), and the proportion of z-scheme electron transport pathway. Inversely, LN increased the proportion of the alternative electron transport pathway and non-photochemical quenching (NPQ). The damaged photosystems during limited nitrogen conditions negatively affected lipid accumulation in oleaginous C. vulgaris JNU13. It is therefore essential to maintain a balance between low nitrogen stress and high photosynthetic capacity by regulating the initial nitrogen supply to maximize lipid yield. The results of the present study may be used as a reference for regulating the initial nitrogen supply to enhance oil productivity.