What’s the Different Wavelength Means to Plants

Red light

Among visible light, red and orange light (wavelength 600 ~ 700nm) and blue-violet light (wavelength 400-500nm) are absorbed most by green plants, and only a slight absorption of green light (500 ~ 600nm). Red light is the light quality that was first used in crop cultivation experiments, and is the necessary light for the normal growth of crops. The biological demand for red light ranks first among various monochromatic lights. The material produced under red light makes plants grow taller, while the material produced under blue light promotes the accumulation of egg quality and non-carbohydrates and adds weight to the plant. Red light is built by regulating the photomorphology of photosynthetic pigments, driving photosynthesis through absorption of photosynthetic pigments, promoting stem elongation and carbohydrate synthesis, which is beneficial to the synthesis of VC and sugar in fruits and vegetables, but inhibits nitrogen assimilation. Although red light is indispensable for plant growth, using red light alone to cultivate plants well is still a bit difficult.

Blue light

Blue light is the necessary supplemental light for red light used in crop cultivation, and is the necessary light for normal growth of crops. The amount of light intensity is second only to red light. Blue light inhibits stem elongation, promotes chlorophyll synthesis, facilitates ammonia assimilation and protein synthesis, and facilitates the synthesis of antioxidants. Blue light affects plant phototropism, photomorphogenesis, stomatal opening, and photosynthesis of leaves. Increasing blue light in white light can shorten internodes, reduce leaf area, reduce relative growth rate, and improve N / C efficiency. Chlorophyll synthesis and chloroplast formation in higher plants as well as high chlorophyll a / b ratios and low chloroplasts require blue light. Excessive blue light is not conducive to plant growth and development. The combination spectrum of red and blue light can promote the growth and development of crops seedlings more than only red or blue light. The ratio of red and blue light combination required by different plants is different.

Green light

Green light and red and blue light can harmonize the growth and development of plants. Under red and blue LED compound light, the plant is a little purple-gray, which makes it difficult to diagnose diseases and disorders. It can be solved by adding a small amount of green light. The green light effect is usually opposite to the red and blue light effects. For example, green light can reverse the stomata opening promoted by blue light. Under strong white light, the photosynthetic quantum yield of chloroplasts on the upper surface near the light is lower than that of the lower chloroplasts. Because green light can penetrate the leaves more than red and blue light under strong white light, the absorption of extra green light by the lower chloroplast can increase leaf photosynthesis to a greater extent than the additional absorption of red and blue light. Low light intensity cultivated plants do not need green light, low density and low canopy thickness facility plants do not need green light either, but high light intensity and density and high canopy thickness must require green light.

Yellow and orange light

Yellow light, orange light, green light, and purple light are all important photosynthetically active radiations, but the plant demand is small. Adding yellow light on the basis of red and blue light can significantly increase the growth of spinach seedlings. Yellow light has the best effect on improving the nutritional quality of leaf lettuce, but blue light is more conducive to significantly increasing the content of mineral elements. Adding yellow light and purple light can improve the photosynthetic capacity of cherry tomato seedlings, and relieve the red and blue weak light stress. Compared with white light, violet light and blue light increase the activity of antioxidant enzymes and delay the senescence of plants, while red light, green light and yellow light inhibit the activity of antioxidant enzymes and accelerate the aging process of plants.

FR light

Although 730nm red light is of little significance to photosynthesis, its strength and its ratio to 660nm red light have important effects on the formation of crop plant height and internode length. Through light quality adjustment and R / FR ratio to control plant morphology and plant height. When the ratio becomes larger, the distance between the stem nodes of the plant becomes smaller, the plant becomes shorter, and the propagating plant tends to elongate. The change of the ratio also affects the axillary bud differentiation, chlorophyll content, stomatal index, and leaf area to varying degrees. The selective absorption of red light by plants and the selective transmission of far red light make plants under shade to be in a far-infrared-rich light environment.

Wavelengths below 380nm are called ultraviolet light. According to the physical and biological characteristics of ultraviolet light, the wavelength of 320-380nm is long-wave ultraviolet (UV-A), the wavelength of 280-320nm is medium-wave ultraviolet (UV-B), and the wavelength of 100-280nm is short-wave ultraviolet (UV-C). 95% of the UV reaching the ground is UV-A. In the solar spectrum, PAR, UV and FR light have regulatory functions on plant growth and development. UV radiation reduces plant leaf area, inhibits hypocotyl elongation, reduces photosynthesis and productivity, makes plants vulnerable to attack by pathogens, but can induce flavonoid synthesis and defense mechanisms. Low UV-B radiation causes plants to grow too long, it also hinders the synthesis of plant pigments, and is not easy to cover solanaceous fruits and vegetables. An important feature of plant factories is the lack of UV-A and UV-B radiation in sunlight. The complete absence of UV radiation will bring negative effects on production and affect plant growth and development. Therefore, it is necessary to regulate the level of UV radiation in plant factories. Need to pay attention to the production demand and plant tolerance response law as the basis.