Effect of LED Light Fix on the Growth of Horticultural Crops

On June 10th, the "2018 (Sixteenth) Gaogong LED Industry Summit Forum sponsored by Gaogong LED will start again at the Westin Guangzhou Canton Fair. At that time, high-level companies in the 200+ subdivision area will jointly discuss the post-LED lighting era positioning and strategy.

The types of facilities for gardening facilities mainly include plastic greenhouses, solar greenhouses, multi-span greenhouses, and plant factories. Due to the fact that the construction of the facilities partially obstructs natural light sources, indoor lighting is insufficient, which in turn causes crops to be reduced in production and quality. Therefore, the fill light has played an integral role in the high quality and high yield of facility crops, but it has also become a major factor in the increase of energy consumption and operating costs in the facility.

For a long time, the artificial light sources used in the field of facility horticulture mainly include high-pressure sodium lamps, fluorescent lamps, metal halide lamps, and incandescent lamps. The main disadvantages are high heat production, high energy consumption, and high operating costs. The development of a new generation of light-emitting diodes (LEDs) has enabled the application of low-energy artificial light sources in the field of facility horticulture.

LED has the advantages of high photoelectric conversion efficiency, use of direct current, small size, long life, low energy consumption, fixed wavelength, low heat radiation, environmental protection, etc. Compared with commonly used high-pressure sodium lamps and fluorescent lamps, LEDs not only have light quantity and light quality ( The proportion of light in various wavelengths, etc.) can be precisely adjusted according to the needs of plant growth, and plants can be irradiated at close distance due to their luminescence, so that the number of cultivated layers and space utilization can be improved, and energy saving, environmental protection, and space cannot be replaced by traditional light sources. Efficient use of such functions.

Based on these advantages, LEDs have been successfully used in horticultural lighting, controllable environmental basic research, plant tissue culture, factory planting seedlings, and aerospace ecosystems. In recent years, the performance of LED fill light has been continuously improved, prices have been gradually reduced, and various types of wavelength-specific products have been gradually developed, and its application in the fields of agriculture and biology will be even broader.

This article reviews the current research status of LED in the field of facility horticulture, focusing on the photobiological basis of the application of LED lights, the effect of LED lights on plant photomorphogenesis, nutritional quality and anti-aging, and the construction of light formulations. Application and other aspects of application, and the current problems and prospects of LED fill light technology are analyzed and forecasted.

Effect of LED Light Fix on the Growth of Horticultural Crops

The regulation of light on plant growth and development includes seed germination, stem elongation, leaf and root development, phototropism, synthesis and decomposition of chlorophyll, and flower induction. The lighting environment elements in the facility include the light intensity, light cycle, and spectral distribution. The use of artificial light can adjust the elements without being limited by the weather conditions.

The selective absorption of light by plants, and the perception of light signals by different photoreceptors, it has been found that there are at least three types of photoreceptors in plants, photofrin (absorbing red light and far-red light), cryptochrome (absorbing blue light and Near-ultraviolet light) and ultraviolet light receptors (UV-A and UV-B). The use of a specific wavelength light source to illuminate the crop can increase the photosynthesis efficiency of the plant and accelerate its photomorphogenesis, thereby promoting the growth and development of the plant.

Photosynthesis of plants mainly utilizes red orange light (610~720 nm) and blue violet light (400~510 nm). Using LED technology, it is possible to radiate monochromatic light (e.g., red light with a peak at 660 nm, blue light with a peak at 450 nm) that conforms to the wavelength band of the strongest absorption region of chlorophyll, and the spectral domain is only ±20 nm wide.

It is currently believed that red orange light will significantly accelerate the development of plants, promote the accumulation of dry matter, and the formation of bulbs, tuberous roots, leaf spheres, and other plant organs will cause early flowering and fruiting of plants and play a leading role in plant coloration. Blue and purple light can control the phototropism of plant leaves, promote stomatal opening and chloroplast movement, inhibit stem elongation, prevent plant growth, delay plant flowering and promote the growth of vegetative organs; red-blue LED combination can make up for both monochrome The deficiency of light forms the spectral absorption peak that is basically consistent with the crop photosynthesis and morphogenesis, and the light energy utilization rate can reach 80% to 90%, and the energy saving effect is significant.

The use of LED fill lights in facility gardening can achieve a very significant increase in production. Studies have shown that the number of fruits, total yield, and fruit weight of cherry tomatoes supplemented with 300 μmol/(m··s) LED light strips and LED light tubes 12 h (8:00~20:00) are significantly increased. LED lights with fill light increased by 42.67%, 66.89% and 16.97%, respectively, LED lamp fill light increased by 48.91%, 94.86% and 30.86%. During the whole growth period, the LED light supplement (3:2 red-blue mass ratio, light intensity 300 μmol/(m··s)) can significantly increase the fruit quality and yield per unit area of ​​the guarana and eggplant. 5.3%, 15.6%, eggplant increased 7.6%, 7.8%. Through the whole growth period LED light quality and intensity, duration of air-conditioning, can shorten the growth cycle of plants, improve agricultural products, commercial production, nutritional quality and form value, to achieve efficient garden facilities, energy saving and intelligent production.

Application of LED Light Fixture in Vegetable Seedlings

LED light source regulation of plant morphology, growth and development is an important technology in the field of greenhouse cultivation. Higher plants can sense and accept light signals through photoreceptor pigments, cryptochromes, and photoreceptors to photoreceptors, transmit signals through intracellular messengers, and regulate morphological changes in plant tissues and organs. Photomorphogenesis is the dependence of plants on light to control the differentiation, structure and function of cells, and the establishment of tissues and organs, including the effects on the germination of some seeds, the promotion of apical dominance in inhibiting lateral shoot growth, stem elongation, and tropism. .

Vegetable nursery is an important part of facility agriculture. Continuous rainy weather will cause insufficient light in the facility, seedlings are prone to leggy, and then affect the growth of vegetables, flower bud differentiation and fruit development, and ultimately affect the yield and quality. In production, some plant growth regulators such as gibberellin, auxin, paclobutrazol and chlormequat are used to regulate the growth of seedlings. However, the unreasonable use of plant growth regulators can easily lead to contamination of vegetables and facilities. Human health is not good.

The LED fill light has a lot of advantages to fill light. Applying LED fill light is a feasible way.

In the low-light [0~35 μmol/(m?·s)] experiment under LED light supplement [25±5 μmol/(m··s)], it was found that green light promoted the growth of cucumber seedlings. Red and blue light inhibit young seedlings. Compared with seedling seedling index under natural low light, the index of strong seedlings supplemented with red and blue light increased by 151.26% and 237.98%, respectively, and compared with monochromatic light quality, containing red and blue components. The seedling index of the composite light supplement light treatment increased by 304.46%. The red light energy of cucumber seedlings increased the number of true leaves, leaf area, plant height, stem diameter, dry fresh quality, strong seedling index, root activity, SOD activity and soluble protein content of cucumber seedlings. Supplementing UV-B could increase cucumber seedlings. The content of chlorophyll a, chlorophyll b and carotenoids in seedling leaves, supplemented with red, blue light from LED, significantly increased the leaf area, dry matter quality, and strong seedling index of tomato seedlings, and supplemented with LED red and green light to make tomato seedlings Plant height and stem diameter increased significantly; LED green light supplementation could significantly increase the biomass of cucumber and tomato seedlings, and the fresh and dry weight of seedlings increased with the increase of green light intensity, while tomato seedlings had thick and strong stems. The seedling index increased with the increase of the light intensity of the green light; the combination of the LED red light and the blue light increased the stem diameter, leaf area, dry weight of the whole plant, root-shoot ratio, strong seedling index of the eggplant; compared with the white light, the LED red light Improves the biomass of cabbage seedlings, promotes the elongation and leaf extension of cabbage seedlings; LED blue light promotes the growth of cabbage seedlings, the accumulation of dry matter, and the seedling index, so that the cabbage seedlings Of. The above results show that the advantages of vegetable seedlings developed in combination with light control techniques are very obvious.

The Effect of LED Photo Light on Nutritional Quality of Fruit and Vegetable

Proteins, sugars, organic acids, and vitamins contained in fruits and vegetables are beneficial nutrients for human health. Light quality can affect the content of VC in plants by regulating the activity of VC synthesis and decomposing enzymes, and it regulates protein metabolism and carbohydrate accumulation in horticultural plants. Red light promotes the accumulation of carbohydrates, and blue light treatment is conducive to protein formation. The red-blue combination has a significantly higher effect on the nutritional quality of plants than monochromatic light. Supplementing LED red or blue light can reduce the nitrate content in lettuce, supplementing blue or green light can promote the accumulation of soluble sugar in lettuce, supplementing infrared light is beneficial to the accumulation of VC in lettuce. Complementary blue light can promote the increase of VC content and soluble protein content of tomato; red light and red-blue light treatment can promote the sugar and acid content in tomato fruit, and its sugar to acid ratio is highest under the combination of red and blue light treatment; The combination of red and blue light can promote the increase of VC content in cucumber fruits.

Phenolic substances, flavonoids, anthocyanins and other substances contained in fruits and vegetables not only have an important influence on the color, flavor and commercial value of fruits and vegetables, but also have natural antioxidant activity, and can effectively inhibit or eliminate human free radicals. The use of LED blue light to make the anthocyanin content of eggplant skin significantly increased by 73.6%, while the use of LED red light, red and blue light combination can increase the content of flavonoids and total phenols; blue light can promote lycopene in tomato fruit, The accumulation of flavonoids and anthocyanins, combined with red-blue light, promotes the production of anthocyanins to a certain extent, but inhibits the synthesis of flavonoids. Compared with white light treatment, red light treatment can significantly increase the anthocyanins of lettuce aboveground. Content, but the content of anthocyanin in the aerial parts of lettuce with blue light is the lowest; the total phenolic content of green leaves, purple leaves and red leaf lettuce have larger values ​​under white light, red and blue combined light and blue light treatment, but under the red light treatment It is the lowest value; supplementing with LED ultraviolet or orange light can increase the content of phenolic compounds in lettuce leaves, while supplemental green light can increase the content of anthocyanins. Therefore, the use of LED supplement light is an effective way to regulate the nutritional quality of fruits and vegetables.

The Effect of LED Light Fix on the Anti-aging of Plants

The chlorophyll degradation, rapid protein loss and RNA hydrolysis during plant senescence are mainly manifested as leaf senescence. Chloroplasts are very sensitive to changes in the external light environment, and are particularly affected by light quality. Red light, blue light and red-blue light combination are conducive to chloroplast morphogenesis. Blue light is beneficial to the accumulation of starch granules in chloroplasts. Red light and far-red light have negative effects on chloroplast development. The combination of blue light, red light, and blue light can promote the synthesis of chlorophyll in cucumber seedling leaves, and the combination of red and blue light can delay the decay of leaf chlorophyll content in the later period. This effect is more pronounced with the decrease of the proportion of red light and the increase of the ratio of blue light. The chlorophyll content of leaves of cucumber seedlings treated with LED combination of red and blue light was significantly higher than that of the control of fluorescent light and monochromatic red and blue light. The blue light of LED could significantly increase the chlorophyll a/b value of wort and rapeseed.

The changes of cytokinin (CTK), auxin (IAA) and abscisic acid (ABA) and changes of various enzyme activities during the leaf senescence. The content of phytohormones is easily influenced by the light environment, and different light qualities have different regulation effects on phytohormones, and the initial steps of the light signal transduction pathway involve cytokinins. CTK promotes the expansion of leaf cells, enhances the photosynthesis of leaves, inhibits the activity of ribonuclease, DNAzyme and protease, delays the degradation of nucleic acids, proteins and chlorophyll, and thus can significantly delay leaf senescence. There is an interaction between light and CTK-mediated developmental regulation, and light energy stimulates the increase of endogenous cytokinin levels. When plant tissues are in senescence, their endogenous cytokinin content decreases. The IAA is mainly concentrated in areas where growth is vigorous, and there is little content in aging tissues or organs. Purple light can increase the activity of indole acetic acid oxidase, and low IAA level can inhibit the elongation and growth of plants. ABA mainly formed in the senescent leaf tissue, mature fruits, seeds and stems, roots and other parts, the ABA content of cucumber and cabbage were lower than white light and blue light.

Peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) are important and light-related protective enzymes in plants. The activity of these enzymes will decrease rapidly. The effects of different light qualities on antioxidant enzyme activities of plants were significant. After 9 days of red light treatment, the APX activity of rape seedlings significantly increased and POD activity decreased; the POD activity of tomato after 15 days of red light and blue light irradiation was higher than that of white light 20.9% and 11.7% respectively. The activity of POD was lowest after green light treatment for 20 days, which was only 55.4% of that of white light. Supplementing with blue light for 4 h could significantly increase the contents of soluble protein, activity of POD, SOD, APX, and CAT of cucumber seedling leaves. In addition, SOD and APX activity gradually decreased with the extension of the illumination time. The activities of SOD and APX under blue and red light decrease slowly but always higher than that of white light. Irradiation with red light reduced the activities of peroxidase, IAA peroxidase, and IAA peroxidase in leaves of tomato leaves, but caused a significant increase in peroxidase activity in leaves of eggplant. Therefore, the adoption of a reasonable LED light supplement strategy can effectively delay the aging of facilities, horticultural crops, and increase yield and quality.

The construction and application of LED light formula

The growth and development of plants is greatly affected by the quality of light and its different compositional proportions. The light formulation mainly includes several factors such as light quality ratio, light intensity, and illumination time. Since the light requirements of different plants are different, and the light requirements at different stages of growth and development will also be different, the best combination of light quality, light intensity, and light time is required for the cultivated plants.

Light quality ratio

Compared with white light and single red and blue light, LED red-blue combined light showed comprehensive advantages on the growth and development of cucumber and cabbage seedlings. When the ratio of red and blue light is 8:2, the stem diameter, plant height, plant dry weight, fresh weight, and strong seedling index of the plant are significantly increased, and at the same time, the formation of the chloroplast matrix, lamellae, and output assimilation products are favorable. When the ratio of red to blue light was 8:1, the plant height, stem diameter, leaf area, strong seedling index, fresh shoot and whole plant fresh weight of cucumber seedlings were the highest, and the seedling leaves had higher POD and APX activity; When the ratio of blue light was 6:3, the root activity, leaf soluble protein, soluble sugar content and net photosynthetic rate of cucumber seedlings were the highest, and SOD activity was relatively high. The combination of red, green and blue substances was beneficial to the accumulation of dry matter in red bean sprouts, and the addition of green light promoted the dry matter accumulation of red bean sprouts, with the most obvious increase in the ratio of red, green and blue 6:2:1. The red-blue ratio of 8:1 treatment of red bean sprouts hypocotyl elongation best effect, red and blue ratio of 6:3 treatment of red bean sprouts hypocotyl elongation inhibition is obvious but the highest soluble protein content. When loofah seedlings were irradiated with 8:1 red and blue light, the loofah seedlings had the highest seedling index and the highest soluble sugar content. When the ratio of red to blue light was 6:3, the chlorophyll a of the loofah seedling was used. Content, chlorophyll a/b ratio, and soluble protein content were the highest. When the ratio of red to blue light ratio of 3:1 was used for celery, the height, petiole length, leaf number, dry matter quality, VC content, soluble protein content and soluble sugar content of celery could be effectively promoted; in tomato cultivation, Increase the ratio of blue to blue light to promote the formation of lycopene, free amino acids and flavonoids, and increase the proportion of red light to promote the formation of titratable acid; when the ratio of red to blue light is 8:1 for lettuce leaves, it is beneficial to its class. Accumulation of carotene, and effectively reduce its nitrate content and increase VC content.

Light intensity

Plants growing under low light are more susceptible to photoinhibition than under strong light. The net photosynthetic rate of tomato seedlings increased at first and then decreased with increasing light intensity [50,150,200,300,450,550 μmol/(m··s)], and was at 300 μmol/(m··s). ) reached the maximum; the plant height, leaf area, water content and VC content of lettuce increased significantly under light intensity treatment of 150 μmol/(m··s), and the lettuce was grown under the light intensity treatment of 200 μmol/(m··s). The fresh weight, total weight and free amino acid content of the plant were significantly increased, but the leaf area, water content, chlorophyll a, chlorophyll a+b and carotenoids of lettuce were all increased by the light intensity of 300 μmol/(m··s). Decrease; Compared with darkness, with the increase of LED light intensity [3, 9, 15 μmol/(m··s)], the contents of chlorophyll a, chlorophyll b, and chlorophyll a+b in black bean sprouts significantly increased. When the light intensity is 3μmol/(m··s), the content of VC is the highest, and the content of soluble protein, soluble sugar and sucrose is the highest when the concentration is 9μmol/(m··s). With the same temperature, the intensity of light[(2~2.5) When lx×103 lx, (4~4.5) lx×103 lx, (6~6.5) lx×103 lx] increase, the seedling time of pepper seedlings shortens and the soluble sugar content increases, but chlorophyll a and carotenoids increase. The content gradually decreased.

Illumination time

Appropriately prolonging the illumination time can alleviate the weak light stress caused by lack of light intensity to a certain extent, and contribute to the accumulation of photosynthetic products of horticultural crops, so as to increase the yield and enhance the quality. The VC content of sprouting vegetables increased gradually with the prolongation of light duration (0,4,8,12,16,20 h/day), while the free amino acid content, SOD and CAT activity all showed a decreasing trend; with the illumination time ( After 12th, 15th, and 18th hours of extension, the fresh weight of Chinese cabbage plants increased significantly. The contents of VC in leaves and stems of Chinese cabbage were highest at 15 and 12 h, respectively. The contents of soluble protein in leaves of Chinese cabbage were gradually decreased, but the stems were treated with 15 h. The highest; the content of soluble sugar in the leaves of Chinese cabbage was gradually increased, and the highest was 12 hours. When the ratio of red to blue light was 1:2, the 20h light treatment reduced the relative content of total phenols and flavonoids in the green leaf lettuce compared to the 12 h light time, but when the ratio of red to blue light was 2:1, The 20h light treatment significantly increased the relative content of total phenols and flavonoids in green leaf lettuce.

From the above, we can see that different light formulations have different effects on photosynthesis, light morphogenesis, and carbon and nitrogen metabolism in different crop species. How to obtain the best light formulation, light source configuration, and intelligent control strategy requires plant species as an entry point , and should be based on horticultural crops, demand for goods, production goals, production factors and other conditions to make appropriate adjustments to achieve energy-saving light conditions under the conditions of intelligent control and horticultural crops high quality and high yield goals.

Problems and prospects

The significant advantage of LED fill light is that it can be intelligently combined and adjusted according to the photosynthetic characteristics, morphological build, quality and yield demand spectrum of different plants. Different kinds of crops and different growth stages of the same crop all have different requirements for light quality, light intensity, and photoperiod. This requires the further development and improvement of light formulation research, the formation of a huge database of light formulations, combined with the research and development of professional lamps, to achieve The greatest value of LED fill light in agricultural applications, so as to better save energy, improve production efficiency and economic benefits.

The application of LED lights in gardening facilities has shown strong vitality, but the price of LED lights is higher and the one-time investment is larger. The light requirements for various crops under different environmental conditions are not clear, and the light spectrum is supplemented. The intensity and fill time are not reasonable enough to cause various problems in the application of fill light.

However, with the advancement and improvement of technology and the reduction of the production cost of LED fill light, LED light supplement will be more widely used in the facility gardening. At the same time, the development and progress of the LED light-filling technology system combined with new energy will enable the rapid development of factory-based agriculture, family agriculture, urban agriculture and space agriculture to meet people's demand for horticultural crops under special circumstances.