Light with different light quality or wavelength has distinct biological effects, including different effects on plant morphology, chemical composition, photosynthesis and organ growth and development.
1, red light
Red light generally inhibits internode elongation, promotes tillering and increases the accumulation of chlorophyll, carotenoids and soluble sugar. Red light promoted the growth of leaf area and accumulation of beta carotene in pea seedlings; near-ultraviolet light was applied after lettuce seedlings were pre-irradiated with red light, and it was found that red light enhanced the activity of antioxidant enzymes and increased the content of near-ultraviolet absorption pigments to reduce the damage of near-ultraviolet light to lettuce seedlings; full-light experiment on Strawberry showed that red light was beneficial to lettuce seedlings. In order to improve the content of organic acids and total phenols in strawberry.
2, Blu ray
Blue light can significantly shorten the pitch of vegetable nodes, promote the lateral extension of vegetable and reduce the leaf area. At the same time, blue light can also promote the accumulation of secondary metabolites in plants. In addition, it was found that blue light could alleviate the inhibition of red light on photosynthetic system activity and photosynthetic electron transfer ability of cucumber leaves, so blue light was an important factor affecting photosynthetic system activity and photosynthetic electron transfer ability. There are obvious species differences in plants'need for blue light. The effect of 470 nm blue light on anthocyanin and total phenol content in strawberry was obvious after harvesting.
3, green light
Green light has always been a controversial light quality. Some scholars believe that it can inhibit the growth of plants, resulting in dwarf plants and reduced vegetable yields. However, there are also many reports about the positive effect of green light on vegetables. Low proportion of green light can promote the growth of lettuce. Adding 24% of green light on the basis of red and blue light can promote the growth of lettuce.
4, yellow light
Yellow light basically inhibits plant growth, and because many researchers incorporate yellow light into green light, there is little literature on the effects of yellow light on plant growth and development.
5. Ultraviolet light
Ultraviolet light is generally more likely to kill organisms, reduce leaf area, inhibit hypocotyl elongation, reduce photosynthesis and productivity, and make plants more susceptible to infection. However, proper supplementation of ultraviolet light can promote the synthesis of anthocyanins and flavonoids, promote the synthesis of polyphenols by adding a small amount of UV-B to Postharvest cabbage, and postharvest UV-c treatment can slow down the pectin dissolution, mass loss and softening process of red pepper, thus significantly reducing the decay rate and prolonging the quality of red pepper. It can also promote the accumulation of phenolics on the surface of red pepper. In addition, ultraviolet and blue light also affect the elongation and asymmetric growth of plant cells, thus affecting the directional growth of plants. Ultraviolet-B radiation causes changes in the phenotype of dwarf plants, small thick leaves, short petioles, increased axillary branching and root/crown ratio.
6. Far Red Light
Far red light is usually used in combination with red light. Because of the structure problem of photosensitive pigments which absorb red light and far red light, the effects of red light and far red light on plants can be transformed and counteracted each other. When the white fluorescent lamp in the growth room was used as the main light source, the far red radiation (emission peak 734 nm) was supplemented by LED. The contents of anthocyanin, carotenoid and chlorophyll decreased, while the fresh weight, dry weight, stem length, leaf length and leaf width increased. The effect of FR supplementation on growth may be due to the increase of light absorption caused by the increase of leaf area. Arabidopsis thaliana treated with low R/FR had bigger and thicker leaves, higher biomass and more soluble metabolites than that treated with high R/FR, which improved cold resistance.
