The maintenance of life in nature depends entirely on the supply of energy, and the sun is the source of energy. Plants absorb energy from the sun in photosynthesis, produce nutrients needed for plant growth through photosynthesis, and exchange carbon dioxide and oxygen with the outside world through respiration. Photosynthesis and respiration are the two main processes of plant growth.
Photosynthesis is the absorption of solar energy by green plants, which initiates two chemical reactions, light action and enzyme catalysis, which absorb carbon dioxide and water in the air to produce organic substances such as carbohydrates, proteins, fats, and at the same time release oxygen.
Photosynthesis is done in the chloroplast. Chloroplasts in plant cytoplasm contain chlorophyll and enzymes, which are the main substances that absorb and transmit light energy during photosynthesis. The chlorophyll of higher plants has two kinds, a and b. Chlorophyll a is blue-green and chlorophyll b is olive green. Among the red, orange, yellow, green, cyan, blue, and purple components contained in sunlight, chlorophyll has the strongest ability to absorb red and blue light.
There are millions of green plants in nature, and the photosynthesis process in all kinds of green plants is the same. It is estimated that about 3 million tons of CO 2 and 1.1 million tons of water per minute on the earth are converted into 2.1 million tons of oxygen and 2 million tons of organic matter by photosynthesis.
Second, the solar spectrum and the role of various colors of light
1) Visible light: There are three parts of sunlight, such as visible light, ultraviolet light and infrared light. This is the solar spectrum. The red, orange, yellow, green, cyan, blue, and purple lights are visible light, and the wavelength ranges from 700 to 400 nanometers, accounting for 71% of the total solar radiation. When the visible part of the plant surface is reached, 5% is reflected off, 2.5% is transmitted through the blade, and 42.5% is absorbed (about 40% of which is used for transpiration and heat, and about 2.5% is lost by radiation by the leaf surface, only about 0.5~) 1.0% energy is used for photosynthesis).
Among visible light, the most absorbed by green plants are red orange light (wavelength 600-700 nm) and blue violet light (wavelength 400-500 nm), which has only a slight absorption of green light (500-600 nm). The substance produced under red light makes plants grow taller. The substance produced under blue light promotes the accumulation of protein and non-carbohydrate and makes plants gain weight.
2) Ultraviolet light: Light with a wavelength of less than 400 nm is ultraviolet light, accounting for 7% of the amount of solar radiation. Among them, the wavelength is 300-400 nm, which is near-ultraviolet, the wavelength is 200-300 nm, and the wavelength is less than 200 nm, which is vacuum ultraviolet. High-intensity ultraviolet light of less than 300 nanometers is harmful to plants, and ultraviolet rays of less than 280 nanometers can kill plants.
The ultraviolet rays radiated by the sun are mostly absorbed after passing through the atmosphere, especially the ozone layer. There is very little UV light reaching the ground. The role exhibited by ultraviolet light is often advantageous. It plays an important role in the shape, color and quality of plants. The high content of ultraviolet rays in the mountains and plateaus makes the stems and leaves of the plants short and dark, which plays a good role in fruit ripening and can increase the sugar content of the fruits. It can inhibit the action of the appendage, promote the absorption of phosphorus and aluminum, and facilitate the formation of various pigments.
3) Infrared: Light with a wavelength of 700 to 3000 nm is infrared light, accounting for about 22% of the total solar radiation, of which 15% is reflected off, 12.5% â€‹â€‹is transmitted through the blade, and 22.5% is absorbed by the blade. Infrared light increases the temperature and temperature and provides the heat needed by the plant.
In short, red and blue-violet light are most effective for photosynthesis in green plants. Chlorophyll in green plant chloroplasts mainly absorb red and blue-violet light in sunlight. Carotenoids mainly absorb blue-violet light, which means that red light and blue-violet light are most effective for photosynthesis light.
Third, the method of adding red and blue light
1, colored film and light film
The colored film is a plastic film with an organic dye, and the light-transfer film is a plastic film with an organic rare earth compound. The colored film allows selective transmission of seven-color sunlight, and the light-transfer film converts green light into red and blue light.
People can choose artificial colors of different colors to artificially adjust the composition of visible light. Covering the seedlings with light blue vinyl plastic is stronger than covering the colorless film. Flower plants in artificial light with twice the amount of natural light, the growth will be 50 to 70% higher than under natural conditions; planted in a red light environment, its growth rate is increased by more than 40% than the control.
2, light-emitting diodes (LED)
Light-emitting diodes are a type of semiconductor. The light-emitting diode light source is highly illuminating and consumes a small amount of electricity. Irradiation with different diode sources has a significant effect on the growth, chlorophyll content and root weight of the flower seedlings. Orange red and blue violet light are advantageous.
3, plant lights
The main spectrum of the plant lamp is concentrated in the blue and red regions. Scientists have found that the spectral energy distribution of this kind of luminaire is very close to the efficiency curve of plant photosynthesis (more significant for green plants) and is the best source of plant growth. Luminaires that promote plant photosynthesis use three-band tubes with wavelengths of 430 nm, 555 nm, and 630 nm. This kind of lamp can promote the metabolism of flowers and accelerate the photosynthesis of flowers.
Fourth, the light-filling factors affecting plant growth
Modern agricultural plants that control and regulate the industrial processes of plants by using plant growth lighting in greenhouse greenhouses. The advantage of this approach is that it can get rid of the impact of natural climate change on crop growth, so that the entire agricultural production process is always in a controllable state.
The illumination factors that affect plant growth are mainly light intensity, illumination wavelength and illumination time.
Light intensity: According to botany theory, only a certain intensity of light stimulation can cause effective photosynthesis of plants. According to the growth characteristics of different plants, the light intensity suitable for photosynthesis of plants is generally 2000-5000 lux.
Light wavelength: According to botany theory, different wavelengths of light have different effects on plant growth. On the basis of natural light, the addition of blue and red bands of complementary illumination has a significant effect on regulating plant growth.
Illumination time: The photosynthesis of plants has its own rules. Generally speaking, in the daytime, plants absorb sunlight and produce photosynthesis. At night, plants exchange carbon dioxide and oxygen under respiration.
In the modern agricultural factories that have been built, most of them are equipped with lighting devices that promote plant growth, and provide supplementary illumination to plants through close-range illumination.
Such a lighting device can control the intensity and time of illumination by a pre-implanted procedure according to the needs of plant growth, thereby promoting plant growth.
China is a big agricultural country. Breakthroughs in this area will not only increase crop yields, improve quality, but also make efficient use of land resources. Therefore, vigorous research on the selective absorption of plant growth and development in the optical band, according to the influence of different spectral components on plant growth and development, the development and application of plant-specific lighting equipment will bring huge economic and social benefits.
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