5.Effects of LED lights with different light quality on plant growth quality
Light quality has great influence on plant growth, photosynthetic characteristics, yield and quality. For most plants, red light increases leaf area. The leaves of radish seedling, Chinese toon seedling, tomato, cucumber seedling, tobacco, straw poison and lettuce expanded rapidly and the leaves were larger under red light treatment. Blue light also increases leaf area, but blue light inhibits leaf expansion in tobacco, poinsettia, and clover. The addition of blue light to red light can significantly improve the leaf area of lettuce. The leaf area of spinach under red, blue and yellow light treatment was significantly larger than that of other treatments. Red light treatment is beneficial to the accumulation of dry matter in tomato, eggplant, cucumber, lettuce and other crops. Red and blue composite light increased the biomass of pepper, phalaenopsis, osmanthus and cucumber. The addition of green light, yellow light, purple light and white light on the basis of the combination of red and blue light had significant effects on the biomass of lettuce, cherry tomato and cabbage without bulb.
Red light is beneficial to the accumulation of plant carbohydrates. Red light treatment can significantly increase the soluble sugar content of spinach, cucumber, pepper, tomato seedlings and radish sprouts. Red light can promote the accumulation of starch, which has been reported in soybean, cotton, oilmallow sprout and brassica napus. Because the output of photosynthetic products in leaves can be inhibited by red light, starch accumulates in leaves. The change of soluble protein content in leaves is one of the reliable indicators to reflect the physiological function of leaves. Blue light is good for protein synthesis. Blue light increased soluble protein content in pea seedling, lettuce, cucumber and sprout. Blue light significantly increased the total amino acid and sugar content in chrysanthemum leaves. The current study found that blue light can significantly promote dark respiration of mitochondria, and the organic acids produced in the respiration process can serve as the carbon framework for the synthesis of amino acids, which is conducive to protein synthesis.
Complex spectra also have different promoting effects on photosynthetic products of plants. Yellow light is beneficial to the synthesis of soluble sugar and protein in lettuce, the formation of sucrose content in tomato and the accumulation of free amino acid in rapeseed sprout.
6.Effects of light quality on vegetable quality
Light energy affects many physiological processes of plants, especially plays an important role in photosynthesis and plant morphogenesis. Rational utilization of specific light waves is conducive to improving nutritional quality of vegetables.
Different light quality has different effects on the formation of secondary metabolites in plant organs. Compared with white light, red light, blue light and mixed red and blue light can promote the degradation rate of chlorophyll in the fruits of colored sweet pepper and increase the synthesis rate of carotenoids and anthocyanins, while slow down the synthesis rate of flavonoids. Blue light can induce the accumulation of flavonoids and anthocyanins, and increasing the ratio of blue light can promote the formation of lycopene and flavonoids in tomato fruits.