Response of lipid productivity to photosynthesis of Chlorella vulgaris under various nutrient stress modes

Abstract

Chlorella vulgaris is a valuable source of lipids that can be used for biodiesel. Chlorella can effectively absorb nitrogen (N) and phosphorus (P), which can change growth characteristics, intracellular components, and photosynthesis capacity. This research analyzes the photoautotrophic cultivation of Chlorella under various nutrient modes, aiming to identify the conditions with maximum lipid production and enhanced photosynthesis. Results show that nutrient stress affects the biomass, morphology, and lipid productivity significantly. The optimal lipid content (61.77 mg·L−1 for N, 3.56 mg·L−1 for P, and a combination of concentrations 123.53 mg·L−1 for N and 3.56 mg·L−1 for P), increases by >57%, >37%, and >18%, respectively. The maximum lipid production, achieving >124 mg L−1 and increasing by >40%, is usually accompanied by a high level of photosynthetic capacity. Lipid production and actual photochemical quantum yield decrease gradually with increasing nutrient concentrations, so that high environmental stress on algae leads to a significant decrease in the maximum quantum yield under excessive nutrient concentrations. Similarly, the electron transfer rate also shows a decreased level with increasing nutrient concentrations. The ΔFν/Fm can be used for estimating lipid accumulation, and was proposed to be 0.18–0.20. This study indicates that different responses of photosynthetic capacity have an effect on lipid accumulation under various nutrient modes and that the photosynthetic capacity can be used to forecast lipid accumulation.