Analysis of the effects of various light spectra on microgreen species

Light conditions, such as spectral composition, intensity and photoperiod, can affect the photosynthetic apparatus and content of beneficial bioactive compounds. The experiments realised under randomised experimental design tested seedlings of 21 genotypes, including 12 genotypes of the Brassicaceae family, lettuce, amaranth, onion, spinach, fenugreek and two beet and two basil genotypes, which were cultivated in three light environments under narrow-band red and blue light-emitting diodes (LEDs) and broad-band white LEDs. Responsiveness to light spectra was assessed based on fresh and dry weight, total chlorophyll and carotenoid contents and non-invasive assessment of specific compounds using fluorescence excitation ratios. In white light, we observed a higher fresh weight compared to that in monochromatic environments, especially compared to blue light. In most of the species, blue and white light had a positive effect on the concentration of chlorophyll and carotene in plants compared to red light. Blue light was associated with the highest values of chlorophyll excitation ratios, indicating a significant increase in flavonoids and anthocyanin contents. Individual microgreens responded differently in all assessed traits, especially in fluorescence ratios. We also observed the clustering of microgreens with similar responses to LED light spectra. In conclusion, in most plant species, multispectral white LEDs positively influenced quantitative and qualitative traits compared to the most frequently used red LEDs. Blue light slightly improved quality, but suppressed growth. Nevertheless, some species responded differently, emphasising the need to optimise the light to improve the microgreens’ production and nutritional value.