Photosynthetic activity and biocomponent production of Isochrysis galbana regulated by manipulated light quality

To investigate how light quality regulates the biocomponent production and photosynthetic activities of Isochrysis galbana, monochromatic light of green (G), red (R), blue (B), and combinations of R and B (R: B=n: m, nRmB, n + m=7) were compared with achromatic white light (W) in this study. The results showed that B and blue-dominant light (1R6B-2R5B) reduced pigment concentrations, growth rates, and production of biomass and biocomponents compared to W, whereas G matched W. R had lower growth rate and biomass production than W but achieved the highest contents of carbohydrate, protein, and pigments. The combination 6R1B produced the highest biomass (480.28 mg/L), protein (99.19 mg/L), and lipid (213.44 mg/L), while 4R3B toped carbohydrate production (70.39 mg/L). G showed the highest energy dissipation and lowest photosynthetic parameters, whereas R had the highest electron transfer efficiency and pigment content. Mechanistically, red and blue combinations enabled the reaction center (RC) achieved the high electron transfer energy and low dissipated energy despite low absorption energy. Red-dominant combinations further offset the limit of absorption, boosting photosynthetic performance and biocomponent production. These findings clarify the regulatory role of light quality on algal photosynthesis and guide artificial irradiation for I. galbana biocomponent production.