The relationship between light spectrum and plant photosynthesis

The relationship between light spectrum and plant photosynthesis

The relationship between light spectrum and plant photosynthesis in recent years, the effect of light quality on plant growth and morphology has attracted the attention of researchers. For example, Japanese scholars focused on the effect of LED monochromatic light on the growth characteristics of tissue culture seedlings. In Israel, different colors of plastic sheeting were used as covering materials to explore the effects on the growth of leafy vegetables and foliage plants. The most famous literature on the relationship between light quality and plant development is "Photo morphogenesis in Plant", written by R. E. Kendrick and G. H. M. Kronenberg (1986, Martinus Nijhoff Publishers). The data are as follows: the effect of light spectrum on plant physiology is very small. 315 ~ 315nm has little effect on morphological and physiological process, 315 ~ 400nnm has little chlorophyll absorption, affects photoperiod effect, prevents stem elongation from 400 ~ 520nm (blue) chlorophyll to carotenoid absorption ratio is the largest, and has the greatest effect on photosynthesis 520 ~ 610nm pigment absorption rate is not high 610 ~ 720nm (red) chlorophyll absorption rate is low. It has a significant effect on photosynthesis and photoperiod effect. 720 ~ 1000nm absorption rate is low, stimulating cell prolongation, affecting flowering and seed germination > 1000nm conversion into heat in the 7 (2) issue of Flower Tech in 2004. there is an article discussing the effect of light color on photosynthesis. The writer is Mr. Harry Stijger. The subtitle of the article indicates that it is generally believed that the effect of light color on photosynthesis is different, in fact, in the process of photosynthesis, the influence of light color is not different, so the use of full spectrum is most beneficial to plant development. The sensitivity of plants to spectra is different from that of human eyes. The most sensitive spectrum of human eyes is 555nm, which is between yellow and green light. It is less sensitive to blue light and red light. On the other hand, plants are most sensitive to red light and less sensitive to green light, but the difference in sensitivity is not as great as that of human eyes. The most sensitive area of plant to spectrum is 400~700nm. The spectrum of this region is usually called the effective energy region of photosynthesis. About 45% of the energy of sunlight is in this spectrum. Therefore, if the artificial light source is used to supplement the amount of light, the spectral distribution of the light source should also be close to this range. The photon energy emitted by a light source varies from wavelength to wavelength. For example, the energy of the wavelength 400nm (blue light) is 1.75 times that of 700nm (red light). But for photosynthesis, the effect of the two wavelengths is the same. The excess energy in the blue spectrum that cannot be used as photosynthesis is converted into heat. In other words, the photosynthetic rate of plants is determined by the number of photons absorbed by plants in 400~700nm, but not related to the number of photons emitted by each spectrum. But it is generally believed that the color of light affects the rate of photosynthesis. Plants are different in sensitivity to all spectra. This reason comes from the special absorption of pigment (pigments) in leaves. Among them, chlorophyll is the best known. But chlorophyll is not the only pigment useful for photosynthesis. Other pigments are also involved in photosynthesis, so the photosynthetic efficiency can not only take into account the absorption spectrum of chlorophyll. The difference of photosynthetic pathway is also not related to color. Light energy is absorbed by chlorophyll and carotene in leaves. Energy is converted into glucose and oxygen by two photosynthetic systems that fix water and carbon dioxide. This process uses the spectrum of all visible light, so there is little difference in the effect of light sources of various colors on photosynthesis. Some researchers believe that there is the greatest photosynthetic capacity in the orange light part. But this does not mean that plants should be cultivated in this monochromatic light source. For the morphological development and leaf color of plants, plants should receive a variety of balanced light sources. Blue light source (400~500nm) is very important for plant differentiation and stomatal regulation. If the blue light is not enough, the proportion of far red light is too much, the stem will grow too much, and it is easy to cause leaf yellowing. When the ratio of red light spectrum (655~665nm) energy to far red light spectrum (725~735nm) energy is between 1. 0 and 1. 2, the plant development will be positive. But each plant has different sensitivity to these spectral ratios. The high pressure sodium lamp is often used as the artificial light source in the greenhouse. Take the Philips Master SON-TPIA light source as an example, it has the highest energy in the orange spectrum region. However, the energy of far infrared light is not high, so the energy ratio of red light to far red light is greater than 2.0. However, because there is still natural sunlight in the greenhouse, it does not cause the plants to become shorter. (if this light source is used in the growth box, it may have an impact.) In natural sunlight, blue light accounts for 20% of the energy. For artificial light sources, such a high proportion is not required. For normally developing plants, most plants need only 6 per cent of blue light within the range of 400~700nm. In the natural sunlight, there is enough blue light energy. Therefore, the artificial light source does not need to add more blue light spectrum. However, when the natural light source is insufficient (such as winter), the artificial light source needs to increase the blue light energy, otherwise the blue light source will become the limiting factor of plant growth. However, if the light source improvement method is not used, there are still other ways to remedy the lack of light source. Such as temperature regulation or the use of growth hormones.

Reference materials: science and technology windows / flowers, landscaping, vegetables Yunnan Horticultural Expo