Far-red light (720 or 740 nm) improves growth and changes the chemical composition of Chlorella vulgaris

Far-red (FR) light is crucial for the efficiency of photosynthesis and photomorphogenetic activity. This study investigated whether FR light at different wavelengths affects the Chlorella vulgaris biomass growth rate and chemical composition. For this purpose, FR was added to the blue-red (R) light at the wavelength of 720 nm (BRFR720L [blue + R + FR 720 nm light]) or 740 nm (BRFR740L [blue + R + FR 740 nm light]). BRFR740L allowed both higher growth rate and increased amount of total biomass compared to BRFR720L (blue + R + FR 720 nm light). The chemical composition of C. vulgaris biomass, analyzed by FT-Raman spectroscopy on lyophilized cells, significantly correlated with the applied FR component. The differences in lipid, carotenoid, and chlorophyll contents were particularly evident and all were higher in BRFR740L. Fluorescence emissions spectra of C. vulgaris cells were measured in the range 420-800 nm in the cuvette equipped with a magnetic stirrer preventing sedimentation of the cells during measurement. In the blue-green range (420-650 nm) fluorescence emission spectra indicated that changes in the chemical composition of phenolic compounds in the algae depended on the wavelength of FR used in LED matrices. This work showed that the use of FR of a wavelength 740 nm in the bioreactor's light source significantly improves biomass production of C. vulgaris cultures.