Palette of green: Exploring the effects of different wavelengths of green light on biomass and morphology in lettuce (Lactuca sativa)

It is increasingly evident that green light (500–600 nm) affects plant growth, but the varying effects of different regions within this waveband remain unclear. We investigated how different regions of green light affect lettuce (Lactuca sativa) growth, morphology and physiology. Lettuce was grown in a climate chamber with red/blue light as a reference treatment. In three green light treatments, 28 % of the red/blue light was replaced by green light. A higher fraction of green light logically meant a lower fraction of red and blue light. The green light was provided either by narrowband green LEDs peaking at 515 nm or 550 nm, or by a broadband green LED. In all treatments, light intensity was 212 μmol m⁻² s⁻¹. After 21 days of growth, shoot biomass (+14–29 %) and height (+16–18 %) increased in all green light treatments compared to the reference, while leaf photosynthetic gas exchange and pigmentation remained unchanged. The largest biomass (+29 %) and leaf area (+18 %) were obtained in the narrowband green light treatment peaking at 550 nm. We conclude that the increase in lettuce biomass was not caused by a higher carbon assimilation per leaf area but may instead be explained by improved light distribution within the canopy. Our results suggest that specific regions in the green light waveband are more beneficial to lettuce growth than others.