Five kinds of light sources that LED plant lights affect plant growth
LED plant growth light, better meet the plant's preference for light
The plant growth lamp is an application field derived from LED products. The principle of the plant growth lamp is to use the several wavelengths of plant photosynthesis to focus on supplementing light, so that plants can obtain greater photosynthesis in the same time, of which 400- The wavelength of 520nm and the wavelength of 610-720nm are particularly prominent for the photosynthesis of plants. Therefore, the plant growth lamp focuses on the two spectral bands of 400-520nm and 610-720nm according to the needs of plant growth. The overall lighting is displayed as red. Blue mixed color, which can more effectively supplement light for plant growth.
By supplementing the light with the plant growth lamp, the occurrence of diseases and insect pests and deformed fruits can be reduced, and the crops can bloom or bear fruit earlier, and the output of vegetables and fruits can be increased early on the market, and the economic benefits of planting operations can be effectively improved.
light sources that affect plant growth
Light is the basic environmental factor for plant growth and development. It is not only the basic energy source for photosynthesis, but also an important regulator of plant growth and development. The growth and development of plants is not only restricted by the amount of light or light intensity (photon flux density, photonfluxdensity, PFD), but also by light quality, that is, light and radiation of different wavelengths and their different composition ratios.
The solar spectrum can be roughly divided into ultraviolet radiation (ultraviolet, UV<400nm, including UV-A320~400nm; UV-B280~320nm; UV-C<280nm, 100~280nm), visible light or photosynthetically active radiation (photosynthetically active radiation, PAR, 400~700nm, including blue light 400~500nm; green light 500~600nm; red light 600~700nm) and infrared radiation (700~800nm). Due to the absorption of ozone in the stratosphere (stratosphere), UV-C and most UV-B cannot reach the surface of the earth. The intensity of UV-B radiation reaching the ground changes due to geographic (altitude and latitude), time (day time, seasonal changes), meteorological (cloud layer, thickness, etc.) and other environmental factors such as air pollution. .
Plants can perceive subtle changes in light quality, light intensity, duration and direction of light in the growing environment, and initiate the physiological and morphological changes necessary for survival in this environment. Blue light, red light and far-red light play a key role in controlling the light morphogenesis of plants. The photoreceptors of phytochrome (Phy), cryptochrome (Cry) and phototropin (phototropin, Phot) receive light signals and trigger plant growth and development changes through signal transduction.
The monochromatic light mentioned here refers to light within a specific wavelength range. The wavelength range of the same monochromatic light used in different experiments is not completely the same, and it often overlaps with other monochromatic lights of similar wavelength in different degrees, especially before the appearance of LED light sources with good monochromaticity. In this way, different and even contradictory results will naturally be produced.
Red light
Red light (R) inhibits internode elongation, promotes lateral branching and tillering, delays flower differentiation, and increases anthocyanins, chlorophyll and carotenoids. Red light can cause positive light movement of Arabidopsis roots. Red light has a positive effect on the resistance of plants to biotic and abiotic stresses.
Far red light (FR) can counteract the red light effect in many cases. Low R/FR ratio leads to reduced photosynthetic capacity of kidney beans. In the growth room, white fluorescent lamps are used as the main light source, and LEDs are used to supplement far-red radiation (emission peak 734nm) to reduce the content of anthocyanins, carotenoids and chlorophyll, and make the plant fresh weight, dry weight, stem length, leaf length and leaf length. Width increases. The effect of supplementing FR on growth may be due to the increase in light absorption caused by the increase in leaf area. Arabidopsis thaliana grown under low R/FR conditions has larger and thicker leaves, larger biomass, and strong cold adaptability than plants grown under high R/FR conditions. Different ratios of R/FR can also change the salt resistance of plants.
Blu-ray
Generally speaking, increasing the share of blue light in white light can shorten internodes, reduce leaf area, reduce relative growth rate and increase nitrogen/carbon (N/C) ratio.
Blue light is needed for chlorophyll synthesis and chloroplast formation in higher plants, as well as sun chloroplasts with high chlorophyll a/b ratio and low carotenoid levels. Under red light, the photosynthetic rate of the cells of the algae gradually decreased, and the photosynthetic rate quickly recovered after turning to blue light or increasing some blue light under continuous red light. When the dark-growing tobacco cells were transferred to continuous blue light for 3 days, the total amount of rubulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and the chlorophyll content increased sharply. Consistent with this, the dry weight of cells per unit volume of culture medium also increased sharply, and increased very slowly and slightly under continuous red light.
Obviously, for the photosynthesis and growth and development of plants, red light alone is not enough. Wheat can complete its life cycle under a single red LEDs light source, but in order to obtain tall plants and a large number of seeds, an appropriate amount of blue light must be added (Table 1). The yield of lettuce, spinach, and radish grown under a single red light was lower than that of plants grown under a combination of red and blue light, while the yield of plants grown under a combination of red and blue light with a moderate amount of blue light was comparable to that of plants grown under a cool white fluorescent light. Similarly, Arabidopsis thaliana can produce seeds under a single red light, but compared with plants grown under a cool white fluorescent lamp, as the proportion of blue light decreases (10% to 1%), the red and blue combined light grows Plant bolting, flowering and fruiting are delayed. However, the seed yield of plants grown under a combination of red and blue light containing 10% blue light was only half of that of plants grown under a cool white fluorescent lamp. Excessive blue light inhibits plant growth, shortens internodes, reduces branches, reduces leaf area and reduces total dry weight. There are obvious species differences in the blue light needs of plants.
It needs to be pointed out that although some studies with different types of light sources show that the differences in plant morphology and growth are related to the different proportions of blue light in the spectrum, but the different types of lamps emit different compositions of non-blue light, and their conclusions are still questionable. For example, although the dry weight and net photosynthetic rate per unit leaf area of soybean and sorghum plants grown under the same intensity of fluorescent lamps are significantly higher than those of plants grown under low-pressure sodium lamps, these results cannot be entirely attributed to the blue light under low-pressure sodium lamps. The lack may also be related to too much yellow and green light and too little orange-red light under low-pressure sodium lamps.
Green light
The dry weight of tomato seedlings grown under white light (including red, blue and green light) was significantly lower than that of seedlings grown under red and blue light. The results of spectroscopic detection of growth inhibition in tissue culture showed that the most harmful light quality is green light with a peak at 550nm. The plant height, freshness, and dry weight of marigolds grown under light that removes the green light are 30%-50% higher than those grown under full-spectrum light. Full-spectrum light supplementing green light leads to short plants and reduced dry and fresh weight. Removal of green light strengthens marigold blooming, while supplementation of green light suppresses the flowering of dianthus and lettuce.
However, there are also research reports on green light promoting growth. Kim et al. (2006) summarized the experimental results of red and blue combined light (LEDs) supplementing green light and concluded that plant growth is inhibited when green light exceeds 50%, and plant growth is enhanced when the proportion of green light is less than 24%. Although the addition of green light on the red and blue light background provided by the LED led to an increase in the dry weight of the lettuce above ground, the conclusion that the addition of green light enhances growth and produces more biomass than under cool white light is problematic: (1) The dry weight of biomass they observed is only the dry weight of the above ground. If the dry weight of the underground root system is included, the results may be different; (2) The dry weight of lettuce grown under red, blue and green lights The dry weight of plants grown under cool white fluorescent lamps is likely to be the result that these tri-color lamps contain much less green light (24%) than cool white fluorescent lamps (51%), that is, the green light suppression effect of cool white fluorescent lamps is greater than that of tri-color lamps. The results of light; (3) The photosynthetic rate of plants grown under red and blue combined light was significantly higher than that of plants grown under green light. The results support the previous speculation.
The green light effect is usually the opposite of the red and blue light effects. Green light can reverse the stomata opening promoted by blue light. However, treating the seeds with a green laser can make radishes and carrots grow to twice the size of the control. A dim pulse of green light can accelerate the elongation of seedlings growing in the dark, that is, promote the elongation of the stem. A single green light (525nm±16nm) pulse (11.1 μmol·m-2·s-1, 9s) from an LED light source was used to treat Arabidopsis albino seedlings, resulting in a decrease in plastid transcripts and an increase in stem growth rate.
(2007) Based on the research data of plant photobiology over the past 50 years, the role of green light in plant development, flowering, stomata opening, stem growth, chloroplast gene expression and plant growth regulation was discussed. The blue light sensor harmoniously regulates the growth and development of plants. It should be noted that in this review, the green light (500~600nm) is expanded to include the yellow part of the spectrum (580~600nm).
Yellow light
Yellow light (580~600nm) inhibits the growth of lettuce. Using chlorophyll content and dry weight to plot different proportions of red, far red, blue, ultraviolet and yellow light, the results show that only yellow light (580~600nm) can explain the difference in growth effects between high pressure sodium lamps and metal halide lamps. That is, yellow light inhibits growth. Moreover, yellow light (peak at 595nm) inhibits cucumber growth stronger than green light (peak at 520nm).
Some conflicting conclusions about the yellow/green light effect may be due to the inconsistent wavelength range of the light used in those studies. Moreover, since some researchers classify light from 500 to 600 nm as green light, there are few literatures on the effect of yellow light (580 to 600 nm) on plant growth and development.
Ultraviolet radiation
Ultraviolet radiation reduces plant leaf area, inhibits hypocotyl elongation, reduces photosynthesis and productivity, makes plants vulnerable to pathogens, but can induce flavonoid synthesis and defense mechanisms. UV-B can reduce the content of ascorbic acid and β-carotene, but can effectively promote anthocyanin synthesis. UV-B radiation causes dwarf plant phenotypes, small and thick leaves, short petioles, increased axillary branches, and changes in the root/shoot ratio.
Investigation of 16 rice cultivars from 7 different regions in China, India, the Philippines, Nepal, Thailand, Vietnam and Sri Lanka growing in the greenhouse showed that 4 rice cultivars increased the total biomass by adding UV-B Cultivated species (only 1 of which reached a significant level, from Sri Lanka), there are a few cultivars (6 of which reached a significant level); those cultivars that are sensitive to UV-B have significantly reduced leaf area and tiller numbers ; There are 6 cultivars with increased chlorophyll content (2 of them reach a significant level); 5 cultivars have significantly reduced leaf photosynthetic rate, and 1 cultivated species (its total biomass quantity is also obvious Increase).
The ratio of UV-B/PAR is an important determinant of the response of plants to UV-B. For example, UV-B and PAR together affect the morphology and oil yield of peppermint. The production of high-quality oil requires a high level of unfiltered natural light.
It needs to be pointed out that although laboratory studies on the effects of UV-B are useful in identifying transcription factors and other molecular and physiological factors, due to the use of higher UV-B levels, there is no accompanying UV-A and Background PAR is often very low, and the results usually cannot be mechanically extrapolated to the natural environment. Field studies usually use UV lamps to increase or use filters to reduce UV-B levels.
