Abstract
Green light, as part of the photosynthetically active radiation, has been proven to have high photosynthetic efficiency once absorbed by plant leaves and can regulate plant physiological activities. However, few studies have investigated the appropriate and efficient way of using the green light for plant production. Thus, the objective of this study was to investigate a moderate amount of green light, partially replacing red and blue light, for plant growth and development. In this experiment, four treatments were set up by adjusting the relative amount of green light as 0 (RB), 30 (G30), 60 (G60), and 90 (G90) μmol m−2 s−1, respectively, with a total photosynthetic photon flux density of 200 μmol m−2 s−1 and a fixed red-to-blue ratio of 4:1. Lettuce (Lactuca sativa cv. ‘Tiberius’) plant growth and morphology, stomatal characteristics, light absorptance and transmittance, photosynthetic characteristics, and nutritional quality were investigated. The results showed that: (1) shoot dry weight increased by 16.3 and 24.5% and leaf area increased by 11.9 and 16.2% under G30 and G60, respectively, compared with those under RB. Plant stem length increased linearly with increasing green-to-blue light ratio; (2) light transmittance of lettuce leaf under treatments employing green light was higher than that under RB, especially in the green region; (3) stomatal density increased, whereas stomatal aperture area decreased with the increase in the relative amount of green light; and (4) carbohydrate accumulation increased under G60 and G90. Soluble sugar contents under G60 and G90 increased by 39.4 and 19.4%, respectively. Nitrate contents under G30, G60, and G90 decreased by 26.2, 40.3, and 43.4%, respectively. The above results indicated that 15–30% green light replacing red and blue light effectively increased the yield and nutritional quality of lettuce plants.
Highlights
Plants perceive light intensity and photoperiod and light quality, including monochromatic and polychromatic light, as ambient growth environment signals that induce a large number of physiological responses (Kami et al, 2010)
The light transmittance was higher under treatments employing green light than that under RB, whereas the light absorptance was, on the contrary, especially within the green region
Results presented in this study suggested that a moderate amount of green light could enhance the nutritional quality of lettuce plants
Summary
Plants perceive light intensity and photoperiod and light quality, including monochromatic and polychromatic light, as ambient growth environment signals that induce a large number of physiological responses (Kami et al, 2010). There is a misconception that green light is less useful for plant photosynthesis, probably because the light absorption of photosynthetic pigments is relatively low within the green region compared with that within the red and blue regions, especially in the plant canopy (McCree, 1972; Smith et al, 2017). This is the reason that red and blue light, rather than other lights, are widely used in recently developed plant factories with artificial lighting for plant production (Wang et al, 2016). The vital role of green light affecting plant physiological activities was gradually proved in previous studies (Johkan et al, 2012; Wang and Folta, 2013; Materová et al, 2017)
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