Plant Lighting Knowledge: 5 Kinds of Monochromatic Light that Affect Plant Growth
Light is the basic environmental factor for plant growth and development. It is not only a 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, photon flux density, PFD), but also by the 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 (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 (atmosphere), 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 change), meteorology (the presence or absence of clouds, thickness, etc.) and other environmental factors such as atmospheric pollution. . Plants can perceive subtle changes in light quality, light intensity, length and direction of light in the growing environment, and initiate physiological and morphological changes necessary for survival in this environment. Blue light, red light and far-red light play a key role in controlling plant light morphology. Photoreceptors (phytochrome, Phy), cryptochromes (cryptochrome, Cry), and phototropins (phototropin, Phot) accept light signals and initiate plant growth and development changes through signal transduction. The monochromatic light mentioned here refers to the light in a specific wavelength range. The bands of the same monochromatic light used in different experiments are not completely consistent, and often have different degrees of band overlap with other monochromatic lights with similar wavelengths, especially before the appearance of LED light sources with good monochromaticity. In this way, it will naturally produce different or even conflicting results. Red light (R) inhibits internode elongation, promotes lateral branching and tillering, delays flower differentiation, and increases anthocyanins, chlorophyll, and carotenoids. The red light can cause the positive optical movement of Arabidopsis roots. Red light has a positive effect on the resistance of plants to biological and abiotic stresses. Far red light (FR) can cancel the red light effect in many cases. Low R/FR ratio leads to a decrease in the photosynthetic capacity of kidney bean. Using white fluorescent lamps as the main light source in the growth chamber, supplementing the far-red radiation with LEDs (emission peak 734nm) reduces the content of anthocyanins, carotenoids and chlorophyll, and makes the plant fresh weight, dry weight, stem length, leaf length and leaves Width increases. The growth promotion effect of supplementary FR may be due to the increase in light absorption due to the increase in leaf area. The Arabidopsis thaliana grown under low R/FR conditions has larger and thicker leaves, larger biomass, and stronger cold adaptability than plants grown under high R/FR. Different ratios of R/FR can also change the salt resistance of plants. Generally speaking, increasing the blue light share in white light can shorten the internodes, reduce the leaf area, reduce the relative growth rate and increase the nitrogen/carbon (N/C) ratio. Higher plant chlorophyll synthesis and chloroplast formation, as well as high chlorophyll a/b ratio and low carotenoid levels, all chloroplasts need blue light. Under red light, the photosynthetic rate of Umbellaria cells gradually decreased, and the photosynthetic rate quickly recovered after switching to blue light or adding some blue light under continuous red light. When dark-growing tobacco cells were transferred to continuous blue light for 3 days, ribulose diphosphate carboxylase/oxygenase (rubulose-1, 5-bisphosphate Carboxylase/oxygenase, Rubisco) total amount and chlorophyll content increased sharply. Consistent with this, the cell dry weight per unit volume of culture medium also increased sharply, while under continuous red light it increased very slowly. Obviously, for the photosynthesis and growth of plants, it is not enough to have red light. 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, it is necessary to add an appropriate amount of blue light (Table 1). The yield of lettuce, spinach, and radish grown under a single red light is 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 an appropriate amount of blue light is comparable to plants grown under a cold white fluorescent lamp. Similar to this, 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%~1%), red and blue grow under combined light Plant bolting, flowering and fruiting are delayed. However, the seed yield of plants grown under the combination of red and blue with 10% blue light is only half that of plants grown under cool white fluorescent lamps. Excessive blue light inhibits plant growth, internodes become shorter, branches are reduced, leaf area becomes smaller, and total dry weight decreases. There are obvious species differences in the plant's need for blue light. Needs to point out that although some studies using different types of light sources have shown that the differences in plant morphology and growth are related to the different proportions of blue light in the spectrum, but because the composition of the non-blue light emitted by the different types of lamps used is also different, the conclusion is 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 light intensity are significantly higher than those grown under low-pressure sodium lamps, these results cannot be entirely attributed to the blue light under low-pressure sodium lamps. The lack of it may be related to too much yellow and green light and too little orange and red light under the low-pressure sodium lamp. The dry weight of tomato seedlings grown under white light (including red, blue, and green light) was significantly lower than that grown under red and blue light. The results of spectrum detection of growth inhibition in tissue culture showed that the most harmful light quality was green light, with a peak at 550 nm. The height, freshness, and dry weight of marigold plants grown under the light that removes the green light are 30% to 50% higher than those grown under the full spectrum light. The full spectrum light supplementing the green light causes the plants to be short and dry, and the fresh weight is reduced. Removal of green light enhances the flowering of marigolds, while addition of green light inhibits 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 when green light exceeds 50%, plant growth is inhibited, and when green light ratio is less than 24%, plant growth is enhanced. Although the addition of green light through the green fluorescent light on the red and blue combined light background provided by the LED led to an increase in the dry weight of the lettuce above ground, the conclusion that supplementing green light enhances growth and produces more biomass than cold white light is problematic: (1) The dry weight of the biomass they observed is only the dry weight of the aboveground. If the dry weight of the underground root system is included, the results may be different; (2) the aboveground of lettuce grown under the red, blue and green lights Plants that grow larger than cool white fluorescent lamps are likely to be the result of the green light (24%) of these three-color lamps being much less than that of cool white fluorescent lamps (51%), that is, the green light suppression effect of cool white fluorescent lamps is greater than that of three-color lamps. Lamp results; (3) The photosynthetic rate of the plants grown under the combination of red and blue light is significantly higher than that of the plants grown under the green light, which supports the previous speculation. The green light effect is usually opposite to the red and blue light effects. Green light can reverse the stomatal opening promoted by blue light. However, using green lasers to treat seeds can make radishes and carrots twice as large as the control. A dim green light pulse can accelerate the growth of seedlings growing in the dark, that is, promote stem elongation. Treatment of Arabidopsis albino seedlings with a single green light (525 nm ± 16 nm) pulse (11.1 μmol·m-2·s-1, 9s) from an LED light source resulted in a decrease in plastid transcripts and an increase in stem growth rate. Plant lighting knowledge: 5 types of monochromatic light that affect plant growth (2007) Based on plant photobiology research data from the past 50 years, green light is discussed in plant development, flowering, stomatal opening, stem growth, chloroplast gene expression and plant growth The role of regulation is that the green light sensing system and the red and blue sensors coordinate the growth and development of plants in harmony. Note that in this review, green light (500~600nm) is expanded to include the yellow part of the spectrum (580~600nm).
Yellow light (580~600nm) inhibits lettuce growth. 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 of high-pressure sodium lamps and metal halide lamps. That yellow light inhibits growth. Also, yellow light (peak at 595nm) inhibits cucumber growth more strongly than green light (peak at 520nm).
Some contradictory conclusions about the yellow/green light effect may be due to the inconsistent wavelength ranges used in those studies. Moreover, because some researchers classify light from 500 to 600 nm as green light, there is very little literature on the effect of yellow light (580 to 600 nm) on plant growth and development. Ultraviolet radiation reduces plant leaf area, inhibits hypocotyl elongation, reduces photosynthesis and productivity, and makes plants susceptible to pathogen attack, 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 changes in dwarf plant phenotypes, small and thick leaves, short petioles, increased axillary branches, and root/crown ratio. The investigation results of 16 rice cultivars from 7 different regions of China, India, Philippines, Nibel, Thailand, Vietnam and Sri Lanka grown in the greenhouse showed that the addition of UV-B resulted in an increase in the total biomass Cultivated species (only 1 of which reached a significant level, from Sri Lanka), and a small number of 12 cultivated species (of which 6 reached a significant level); those cultivated for UV-B were significantly reduced in leaf area and number of tillers ; 6 cultivars with increased chlorophyll content (2 of which reached a significant level); 5 cultivars with significantly reduced leaf photosynthetic rate, and 1 cultivar with significantly increased (its total biomass is also obvious increase). The ratio of UV-B/PAR is an important determinant of plant response to UV-B. For example, UV-B and PAR jointly affect mint morphology and oil production. The production of high-quality oil requires high levels of unfiltered natural light. It should be pointed out that although the laboratory research on the influence of UV-B is effective in identifying transcription factors and other molecular and physiological factors, due to the use of higher UV-B levels, there is no UV-A concomitant and Often with very low background PAR, the results usually cannot be mechanically extrapolated into the natural environment. Field studies often use UV lamps to increase or use filters to reduce UV-B levels.
