For a long time, the artificial light source used in the field of facility horticulture mainly includes high-pressure sodium lamp, fluorescent lamp, a metal halogen lamp, incandescent lamp, etc., the prominent shortcoming is high heat production, large energy consumption, and high operation cost. The development of a new type of Light-emitting Diode (LED) makes possible the application of low-energy artificial Light in the field of facility horticulture. LED has high photoelectric conversion efficiency, using a direct current, small volume, long service life, low consumption, wavelength is fixed, the advantages of low heat radiation, environmental protection, compared with the current widespread use of high-pressure sodium lamp and fluorescent lamp, LED light not only, the light quality (the proportion of the various wavelengths of light, etc.) can be according to the needs of plant growth adjustment precision, and because of the cold light irradiation can close plants, thus make the cultivated layer and improve space utilization, realize the traditional light source can replace the energy-saving, environmental protection and space efficient utilization, and other functions.
Based on these advantages, LED has been successfully applied in facilities horticulture lighting, controllable environment basic research, plant tissue culture, plant factory seedling breeding and space ecosystem, etc. In recent years, the performance of LED supplementary lighting has been continuously improved, the price has been gradually reduced, and various products of specific wavelength have been gradually developed, which will be more widely used in the agricultural and biological fields.
Effects of LED Grow Lights on The Growth of Horticultural Crops
The regulating effects of light on plant growth and development include seed germination, stem elongation, leaf and root development, phototropism, synthesis and decomposition of chlorophyll and flower induction. The elements of the lighting environment in the facility include the intensity of light, the cycle of light and the spectral distribution. The artificial supplementary light can be used to adjust the elements without being restricted by the weather conditions.
Plants have selective absorption characteristics of light, and their light signals are sensed by different light receptors. At present, there are at least three types of light receptors in plants, namely, photoreceptors (absorption of red and far-red light), cryptochrome (absorption of blue and near-ultraviolet light) and ultraviolet light receptors (UV-A and UV-b). By irradiating crops with a certain wavelength light source, the photosynthetic efficiency of plants can be improved, the photomorphogenesis of plants can be accelerated, and the growth and development of plants can be promoted. Plant photosynthesis mainly USES red-orange light (610~720 nm) and blue-violet light (400~510nm). With the use of LED technology, monochromatic light (such as red light with a peak of 660nm and blue light with a peak of 450nm) can be radiated to the band of the strongest absorption region of chlorophyll, and the spectral domain width is only + / - 20 nm.
At present, it is believed that red-orange light can significantly accelerate the development of plants, promote the accumulation of dry matter, and the formation of bulbs, roots, leaf balls and other plant organs, causing early flowering and fruiting of plants, playing a leading role in plant color enhancement. Blue and violet light can control the phototropism of plant leaves, promote stomata opening and chloroplast movement, inhibit stem elongation, prevent plants from growing in vain, and delay the flowering of plants and promote the growth of vegetative organs. The combination of red and blue LED can make up for the deficiency of the monochromatic light of the two, and form the spectral absorption peak which is basically consistent with the photosynthesis and morphology of crops. The light energy utilization ratio can reach 80%~90%, and the energy-saving effect is remarkable.
The use of LED supplementary light in gardening facilities can yield significant yield. Studies have shown that the number of fruits, total production and single fruit weight of cherry tomatoes under the light supplement of 300 pa mol/(m squared ·s)LED lamp belt and LED lamp tube 12h (from 8:00 to 20:00) significantly increased, among which the light supplement of LED lamp belt increased by 42.67%, 66.89%, and 16.97%, and the light supplement of LED lamp tube increased by 48.91%, 94.86%, and 30.86%, respectively. In the whole growth period, LED light supplementation [red and blue matter ratio is 3:2, light intensity is 300 mm mol/(m squared ·s)] treatment can significantly increase the fruit quality and yield per unit area of melon and eggplant, increasing by 5.3%, 15.6%, and 7.6% and 7.8% for eggplant. LED light quality and its intensity and duration can shorten the growth cycle of plants, improve the commodity yield, nutrition quality and morphological value of agricultural products, and realize the efficient, energy-saving and intelligent production of horticultural crops in facilities.
Application of LED Grow Lights on Vegetable Seedling
The control of an LED light source on plant morphology and growth is an important technology in the field of greenhouse cultivation. Higher plants can sense and receive light signals through photosensitive pigments, cryptochrome, and photoreceptor systems, and regulate the morphological changes of plant tissues and organs through intracellular messenger conduction. Photomorphogenesis refers to the plant's dependence on light to control cell differentiation, structural and functional changes, and the construction of tissues and organs, including the influence on part of seed germination, promotion of apical dominance to inhibit lateral bud growth, stem elongation, and inducing directional movement.
Vegetable seedling is the important link of facility agriculture. The continuous rainy weather will make the light in the facility insufficient, and the seedling will easily grow in vain, which will affect the growth of vegetables, flower bud differentiation, and fruit development, and ultimately affect their yield and quality. In production, some plant growth regulators, such as gibberellin, auxin, polyazole, and chlorophyll, are used to regulate the growth of seedlings. However, unreasonable use of plant growth regulators is likely to pollute the environment of vegetables and facilities, which is harmful to human health.
LED supplementary light has many advantages, and the application of LED supplementary light is a feasible approach. In the weak light [0 ~ 35 mu mol/(m squared · s)] under the condition of LED light supplement [25 + / - 5 mu mol/(m squared · s)] trials found that green light the elongation growth of cucumber seedlings, red and blue light moderate growth, inhibit seedling compared with natural seedling index under weak light, added red, blue, from index increased by 151.26% and 237.98% respectively, and compared with monochromatic light quality, light quality, and the fill light with red and blue components processing under strong seedling index increased by 304.46%.
Adding red light to cucumber seedlings can improve the true leaf number, leaf area, plant height, stem thickness, dry fresh quality, seedling vigor, root activity, SOD activity and soluble protein content of cucumber seedlings. Adding UV-b can improve the chlorophyll a, chlorophyll B and carotenoid content of cucumber seedlings. Compared with natural light, supplementary LED red light and blue light significantly improved tomato seedling leaf area, dry matter quality and seedling vigor index, while supplementary LED red light and green light significantly increased tomato seedling plant height and stem diameter. The biomass of cucumber and tomato seedlings can be significantly increased by the green light supplement treatment with LED green light, and the fresh and dry weight of seedling increases with the increase of green light supplement intensity, while the stem thickness and seedling vigor of tomato seedlings increase with the increase of green light supplement intensity. LED red and blue light can increase the stem diameter, leaf area, dry weight, root-crown ratio and seedling vigor index of eggplant. Compared with white light, LED red light can improve the biomass of cabbage seedling, promote the elongation of cabbage seedling and the expansion of leaves. LED blue light can promote the coarse growth, dry matter accumulation and strong seedling index of cabbage seedling, and make the cabbage seedling dwarf. The above results showed that the advantages of vegetable seedling cultivated with light control technology were obvious.
Effect of LED Grow Lights on The Quality of Fruits and Vegetables
The protein, carbohydrate, organic acid and vitamin contained in fruits and vegetables are beneficial to human health. Light quality could be regulated and controlled by VC synthesis and decomposition enzyme activity of VC content in the plant, and the garden plants of the metabolism of protein and carbohydrate accumulation regulation function, red light to promote the accumulation of carbohydrates, blue light treatment is beneficial to proteins to form, and the combination of red and blue light on plant nutrition improve effect is significantly higher than the monochromatic light.
Adding LED red or blue light can reduce the nitrate content in lettuce, adding blue or green light can promote the accumulation of soluble sugar in lettuce while adding infrared light can contribute to the accumulation of VC in lettuce. Adding blue light can promote the content of tomato VC and soluble protein. The combination of red and red and blue light treatment promoted the sugar and acid content of tomato fruits, and the ratio of sugar acid was the highest under the combined red and blue light treatment. The combination of red and blue light can improve the VC content of cucumber fruits.
Phenols, flavonoids, anthocyanins and other substances contained in fruits and vegetables not only have important effects on the color, flavor and commercial value of fruits and vegetables but also have natural antioxidant activities, which can effectively inhibit or remove free radicals of the human body.
LED blue light supplementation can significantly increase the content of anthocyanin in eggplant skin by 73.6%, while LED red light and red blue light can increase the content of flavonoid and total phenol. Blue light can promote the accumulation of lycopene, flavonoid, and anthocyanin in tomato fruits. The combined red and blue light can promote the production of anthocyanin to a certain extent, but inhibit the synthesis of flavonoid. Compared with white light treatment, red light treatment significantly increased anthocyanin content in the ground part of lettuce, but blue light treatment had the lowest anthocyanin content in the ground part of lettuce. The content of total phenol in green leaves, purple leaves and red leaves of lettuce was higher in white light, combined red and blue light and lower in red light. Adding LED ultraviolet or orange light can increase the content of phenolic compounds in lettuce leaves while adding green light can increase the content of anthocyanin. Therefore, it is an effective way to use LED light supplement to regulate the quality of fruit and vegetable nutrients.
Effect of LED Grow Lights on Plant Aging
Chlorophyll degradation, protein loss and RNA hydrolysis in the process of plant aging are mainly manifested as leaf senescence. Chloroplasts are very sensitive to changes in the external light environment, especially under the influence of light quality. The combination of red light, blue light and red and blue light contribute to the formation of chloroplast morphology, blue light contributes to the accumulation of starch grains in green leaves, and red and far-red light have negative effects on the development of chloroplast. The combination of blue light and red and blue light can promote the synthesis of chlorophyll in cucumber seedling leaves, and the combination of red and blue light can also delay the decline of chlorophyll content in leaves at the later stage, and this effect is more obvious with the decrease of the proportion of red light and the increase of the proportion of blue light. The chlorophyll content of cucumber seedling leaves was significantly higher than that of fluorescent lamp control and red and blue color treatment. LED blue light can significantly increase the chlorophyll a/b value of the vegetable and the herb.
Changes in the contents of cytokinin (CTK), auxin (IAA), abscisic acid (ABA) and various enzymes during leaf senescence. The content of plant hormones is easily affected by the light environment, and the regulation of plant hormones by different light substances is different, and the initial steps of the optical signal transduction pathway involve cytokines.
CTK promotes the expansion of leaf cells, enhances leaf photosynthesis, inhibits the activity of ribonuclease, deoxyribonuclease, and protease, and delays the degradation of nucleic acid, protein, and chlorophyll, thus significantly delaying leaf senescence. There is an interaction between light and ctk-mediated development regulation, and light can stimulate the increase of endogenous cytokinin levels. When plant tissue is in senescence, the content of endogenous cytokinin decreases.
IAA is mainly concentrated in areas where growth is vigorous, and there is little content in aged tissues or organs. Ultraviolet light can increase the activity of indoleacetic acid oxidase, and low IAA level can inhibit the elongation of plants.
ABA is mainly formed in senescent leaf tissue, mature fruits, seeds, stems, roots and other parts. ABA content of cucumber and cabbage under combined red and blue light is lower than that of white light and blue light.
Peroxidase (POD), superoxide dismutase (SOD), ascorbic acid peroxidase (APX) and catalase (CAT) are important protective enzymes related to light in plants.
The effects of different light quality on the activity of plant antioxidant enzymes were significant. APX activity and POD activity were significantly increased and decreased after 9 days of red light treatment. After 15 days of exposure to red light and blue light, POD activity was higher than that of white light (20.9%) and 11.7%, respectively. The content of soluble protein, POD, SOD, APX and CAT of cucumber seedling could be significantly increased by adding 4h blue light. In addition, the activity of SOD and APX decreased gradually with the extension of illumination time. The activity of SOD and APX in blue light and red light decreased slowly but always higher than that in white light. Red light irradiation significantly reduced the activity of peroxidase, IAA peroxidase and IAA peroxidase in tomato leaves, but significantly increased the activity of peroxidase in eggplant leaves. Therefore, reasonable LED supplementation strategy can effectively delay the aging of gardening plants and improve yield and quality.
Construction and Application of LED Lights Formula
The growth and development of plants are significantly influenced by the light quality and its different composition proportion. As different plants have different needs for light and different needs for light at different stages of growth and development, the best combination of light quality, light intensity and light supplement time is needed for the cultivated crops.
The Ratio of Light Quality
Compared with white light and single red and blue light, LED red and blue light showed comprehensive advantages in the growth and development of cucumber and cabbage seedling.
When the ratio of red and blue is 8:2, the stem size, plant height, plant dry, fresh weight and seedling vigor index of the plant are significantly increased, which is also conducive to the formation of chloroplast matrix and basal granule layer and the output of assimilation products. Under the treatment with the proportion of red and blue at 8:1, the seedling plant height, stem coarseness, leaf area, seedling index, ground part and whole plant fresh quality were the largest, and the seedling leaves had a higher POD and APX activity. When the ratio of red and blue was 6:3, the root activity, soluble protein content, soluble sugar content and net photosynthetic rate of cucumber seedling were the highest, and SOD activity was relatively high.
The combination of the red, green and blue matter was beneficial to the accumulation of dry matter, and the addition of green light promoted the accumulation of dry matter in the rapeseed. The effect of hypocotyl elongation was best when the ratio of red and blue was 8:1 and the ratio of red and blue were 6:3, but the content of soluble protein was the highest.
When the proportion of red and blue light was 8:1, the seedling of the muskmelon had the largest seedling index and the highest content of soluble sugar. When the proportion of red and blue light was 6:3, the chlorophyll a content, chlorophyll a/b ratio and soluble protein content of the seedling were the highest.
When the ratio of red and blue light to celery is 3:1, it can effectively promote the increase of celery plant height, petiole length, leaf number, dry matter quality, VC content, soluble protein content and soluble sugar content. In tomato cultivation, increasing LED blue light ratio promotes the formation of lycopene, free amino acids, and flavonoids, and increasing red light ratio promotes the formation of titrable acids. When the ratio of red and blue to 8:1 is used in lettuce leaves, it is beneficial to the accumulation of carotenoid, effectively reducing the content of nitrate and increasing the content of VC.
Light Intensity
Plants are more susceptible to light suppression in low light than in high light. With the increase of light intensity [50, 150, 200, 300, 450, 550 mm mol/(m squared ·s)], the net photosynthetic rate of tomato seedlings show a trend of first increase and then decrease, and reaches the maximum at 300 mm mol/(m squared ·s). The plant height, leaf area, water content and VC content of lettuce were significantly increased under the treatment of 150 umol /(m squared ·s) light intensity. Under the treatment of 200 umol /(m squared ·s) light intensity, the fresh weight, total weight and free hydroxy acid content of the ground part of the lettuce were significantly increased, while under the treatment of 300 umol /(m squared ·s) light intensity, the leaf area, water content, chlorophyll a, chlorophyll a+b and carotenoid were decreased. Compared with darkness, the content of chlorophyll a, chlorophyll b and chlorophyll a+b in germinated black-bean sprouts increased significantly with the increase of LED supplemental photometric intensity [3, 9 and 15 displacement mol/(m squared ·s)]. The VC content was the highest when the light intensity was 3 plus mol/(m squared ·s), and the content of soluble protein, soluble sugar and sucrose was the highest at 9 plus mol/(m squared ·s). Under the same temperature condition, with the increase of light intensity [(2~2.5) lx 103 lx, (4~4.5) lx 103 lx, (6~6.5) lx 103 lx], the seedling time of pepper seedling is shortened, and the content of soluble sugar increases, but the content of chlorophyll a and carotenoid gradually decreases.
Lighting Time
The light stress caused by insufficient light intensity can be alleviated to a certain extent by appropriately extending the light time, which is conducive to the accumulation of photosynthetic products of horticultural crops and the effect of increasing yield and improving quality. The VC content of bud seedling was gradually increased with the extension of the time of illumination (0, 4, 8, 12, 16, 20h/ day), while the free amino acid content, SOD and CAT activity were all decreased. With the increase of the illumination time (12, 15, 18h), the fresh weight of the cauliflower plant increased significantly. The VC content of vegetable leaf and moss stem was highest at 15 and 12 hours respectively. The content of soluble protein decreased gradually in the leaves of cauliflower, but the highest was treated with the moss stem for 15h. The soluble sugar content in the leaves of the cauliflower gradually increased, while the moss stem was highest at 12h. In the case that the ratio of red and blue is 1:2, the relative content of total phenols and flavonoids in green leaf lettuce is reduced by 20h light treatment compared with 12h light exposure time, but in the case that the ratio of red and blue ray is 2:1, the relative content of total phenols and flavonoids in green leaf lettuce is significantly increased by 20h light treatment.
By above knowable, different light formula on the photosynthesis of different crop types, light morphogenesis and carbon and nitrogen metabolism in the body has different effects, such as how to get the best illumination formula, light source configuration and intelligent control strategy as the breakthrough point, need to plant species and horticultural crops should be based on demand for goods, production target, factors of production conditions, such as proper adjustment, to achieve energy saving light environment intelligent control under the condition of the target of high quality and high yield and horticultural crops.
Existing Problems and Prospects of LED Grow Lights
The significant advantage of LED supplementary light is that it can be intelligently combined and adjusted according to the demand spectrum of photosynthesis, morphological construction, quality and yield of different plants. Different kinds of crops, the same crop growth period are the requirements of light quality, light intensity and photoperiod, which requires further development and improvement of formula research light form large light recipe database, coupled with professional lamps and lanterns of research and development, to achieve the LED on the agricultural application of maximum value as the fill light, to better save energy consumption, improve production efficiency and economic benefit. The application of LED supplementary light lamp in the facility horticulture has shown great vitality but LED supplementary light has a high price and a large one-time investment, and the supplementary light requirements of various crops under different environmental conditions are not clear, the supplementary light spectrum, intensity and supplementary light time are not reasonable, which inevitably leads to various problems in the application of supplementary light lamp.
However, with the development and improvement of technology and the reduction of production cost of LED supplementary lighting, LED supplementary lighting will be more widely used in facility horticulture. At the same time, the combination of the development and progress of LED lighting technology system and new energy will enable the rapid development of factory agriculture, family agriculture, urban agriculture, and space agriculture to meet the needs of people for horticultural crops in special environments. I believe that LED Growing Lights will be more recognized and a broader consumer market.
没有评论:
发表评论