How does the light spectrum affect plant photosynthesis

The relationship between the light spectrum and plant photosynthesis The relationship between the light spectrum and plant photosynthesis In recent years, the influence of light quality on plant growth and morphology has attracted researchers' attention. For example, Japanese academia has focused on discussing the effects of LED monochromatic light on the growth traits of tissue-cultured seedlings. Israel, on the other hand, used plastic sheeting of different colors as covering material to investigate the effects on the growth of leafy vegetables and foliage plants. The most famous document on the relationship between light quality and plant development is the discussion material in "Photo morphogenesis in Plant," whose authors are R. E. Kendrick and G. H. M. Kronenberg (1986, Martinus Nijhoff Publishers). Its information is as follows: Spectral range Effects on plant physiology 280 ~ 315nm Very little effect on morphology and physiological processes 315 ~ 400nnm Little chlorophyll absorption, affects photoperiodic effects, prevents stem elongation 400 ~ 520nm (blue) The absorption ratio by chlorophyll and carotenoids is the largest, and the effect on photosynthesis is the greatest 520 ~ 610nm The absorption rate by pigments is not high 610 ~ 720nm (red) The chlorophyll absorption rate is low, and it has a significant effect on photosynthesis and photoperiodic effects 720 ~ 1000nm Low absorption rate, stimulates cell elongation, affects flowering and seed germination >1000nm Converted into heat In the 2004 issue 7 (2) of the publication Flower Tech, there was an article discussing the effect of light color on photosynthesis. The author was Mr. Harry Stijger. The article's subtitle indicated that people generally believe that light color has different effects on photosynthesis; in fact, during the process of photosynthesis, the influence of light color is not different, so using a full spectrum is most beneficial to plant development. Plants' sensitivity to the spectrum differs from that of the human eye. The spectrum to which the human eye is most sensitive is 555nm, between yellow and green light. Sensitivity to the blue light region and the red light region is relatively poor. Plants are different. They are most sensitive to the red light spectrum and less sensitive to green light, but the difference in sensitivity is not as great as in the human eye. The region of greatest spectral sensitivity for plants is 400~700nm. This spectral region is usually called the photosynthetically active radiation region. About 45% of the energy of sunlight lies in this spectral region. Therefore, if artificial light sources are used to supplement light quantity, the spectral distribution of the light source should also be close to this range. The energy of photons emitted by a light source differs according to wavelength. For example, the energy of a wavelength of 400nm (blue light) is 1.75 times the energy of 700nm (red light). However, for photosynthesis, the results of the two wavelengths are the same. The excess energy in the blue spectrum that cannot be used for photosynthesis is converted into heat. In other words, the rate of plant photosynthesis is determined by the number of photons in the 400~700nm range that plants can absorb, and is not related to the number of photons emitted by each spectrum. However, general common knowledge holds that light color affects the rate of photosynthesis. Plants have different sensitivities to all spectra. This reason comes from the special absorption properties of pigments in the leaves. Among them, chlorophyll is the most widely known. But chlorophyll is not the only pigment useful for photosynthesis. Other pigments also participate in photosynthesis, so the efficiency of photosynthesis cannot be considered only by the absorption spectrum of chlorophyll. Differences in photosynthetic pathways are also unrelated to color. Light energy is absorbed by chlorophyll and carotene in the leaves. Through two photosystems, the energy fixes water and carbon dioxide and converts them into glucose and oxygen. This process uses the spectra of all visible light, so light sources of various colors have almost no different effects on photosynthesis. Some researchers believe that the orange-red light portion has the greatest photosynthetic capacity. But this does not mean that plants should be cultivated under this kind of monochromatic light source. For plant morphological development and leaf color, plants should receive various balanced light sources. Blue light sources (400~500nm) are very important for plant differentiation and stomatal regulation. If blue light is insufficient and the proportion of far-red light is too high, the stem will grow excessively, and leaf yellowing is likely to occur. If the ratio between the energy of the red light spectrum (655~665nm) and the energy of the far-red light spectrum (725~735nm) is between 1.0 and 1.2, plant development will be normal. But each plant's sensitivity to these spectral ratios also differs. In greenhouses, high-pressure sodium lamps are often used as artificial light sources. Taking the Philips Master SON-TPIA lamp source as an example, it has the highest energy in the orange-red spectral region. However, the energy in the far-infrared light is not high, so the red light/far-red light energy ratio is greater than 2.0. But because the greenhouse still has natural sunlight, it does not cause plants to become shorter. (If this light source is used in a growth chamber, it may have an effect.) Under natural sunlight, blue light energy accounts for 20%. For artificial light sources, such a high proportion is not needed. For normally developing plants, most plants only need 6% blue light energy within the 400~700nm range. Under natural sunlight, this sufficient blue light energy is already present. Therefore, artificial light sources do not need to supplement additional blue light spectrum. But when the natural light source is insufficient (such as in winter), artificial light sources need to increase blue light energy; otherwise, the blue light source will become a limiting factor affecting plant growth. However, if light source improvement methods are not used, there are still other methods that can remedy this problem of insufficient light. For example, temperature regulation or the application of growth hormones. Reference: Science and Technology Window/Flowers, Landscaping, Vegetables - Yunnan Horticulture Expo