Spectral effects of green and blue light on lettuce morphology, growth, phytochemicals, and antioxidant capacity are temperature-dependent

Abstract

Substituting green (G; 500–600 nm) for blue (B; 400–500 nm) light has been shown to enhance crop yield in indoor cultivation through increasing leaf expansion and photon capture. This effect is primarily mediated by cryptochrome photoreceptors. However, cryptochrome activity further depends on temperature. In our study, we investigated how B and G light and temperature interactively regulate plant growth, morphology, physiology, and phytochemical accumulation. Two lettuce (Lactuca sativa) cultivars, ‘Rex’ and ‘Rouxai’, were grown under three temperature conditions (20, 24, and 28 ℃) and five spectral treatments composed of B, G, and red (R; 600–700 nm) light (B40G0R60, B30G10R60, B20G20R60, B10G30R60, and B0G40R60). The subscript number represents the percentage of each waveband in photosynthetic photon flux density (PPFD; 400–700 nm). PPFD was maintained at 200 μmol m−2 s−1 with 18-h photoperiod. Our results showed that light spectral quality and temperature interactively influenced lettuce growth and morphology. Within a moderate temperature range (20–24 ℃), substituting G for B light and warmer temperature synergistically enhanced leaf expansion and biomass production. However, at 28 ℃, higher G percentages (i.e., lower B percentages) caused excessive stem elongation and downward leaf rolling, limiting leaf development and overall growth. Moreover, substituting G for B light, combined with warmer temperature, synergistically decreased phytochemical accumulation and antioxidant capacity, likely due to a reduction in reactive oxygen species content and lower oxidative stress. These findings demonstrate that temperature influences cryptochrome-mediated morphological and physiological responses to light quality, which, in turn, affect plant growth and phytochemical accumulation.