3 major applications of LED plant lighting, only the last one is not good

With the continuous deepening of research on semiconductor luminescent materials, the continuous advancement of LED manufacturing technology and the development and application of new materials, the development of LED has made breakthrough progress, and the price has also dropped drastically. Scholars from all countries are concerned. Especially after the successful development of ultra-high brightness LED, it is widely used in the research of plant physiology or cultivation, such as photomorphogenesis, photosynthesis and chlorophyll synthesis research.

1. LED characteristics applied to plant facility cultivation

Light is one of the basic factors for plant growth and development. Light quality has a regulatory effect on plant growth, morphogenesis, photosynthesis, material metabolism and gene expression. Controlling plant morphogenesis and growth is an important technology in the field of facility cultivation through light quality regulation.

The light sources used in the cultivation of traditional plant facilities are generally fluorescent lamps, metal halide lamps, high pressure sodium lamps and incandescent lamps. These light sources are selected according to the adaptability of the human eye to light. The spectrum has many unnecessary wavelengths and has little effect on plant growth. As the fourth generation of new lighting source, LED has the advantages of energy saving, environmental protection, safety and reliability, long service life, short response time, small size, light weight, low heat generation, easy dispersion or combined control, and many other important characteristics different from other electric light sources. .

With the innovation of optoelectronic technology and the decrease of production cost, LED has become the first choice light source in the field of plant cultivation because of the following excellent performance: (1) The spectral performance is good, and pure monochromatic light and composite spectrum can be obtained as needed, and the spectral width is less than ± At 30 nm, the wavelength coincides with the spectral range of plant photosynthetic and photomorphological formation; (2) the effective utilization of light energy can reach 80% to 90%, and can achieve separate control of different light quality and luminous intensity; (3) as cold The light source can illuminate the plant at a close distance, greatly improving the utilization efficiency of the space, and can be used for the multi-layer cultivation stereoscopic combination system, achieving low heat load and miniaturization of the production space; (4) LED is impact resistant, not easily broken, contains no mercury, no Pollution, waste can be recycled, the service life is dozens of times of ordinary light source, and the extra durability also reduces operating costs.

Due to these remarkable features, LEDs are well suited for plant cultivation in controlled facility environments such as plant tissue culture, facility horticulture and lock-up plant plants, and aerospace eco-life insurance systems. However, due to the current high price of LEDs, there is still a need to promote the application of plant facilities. However, with the rapid development of LEDs in the direction of high brightness and low price, LEDs will be widely used in the field of plant cultivation in the near future.

2, LED applied to plant tissue culture

In plant tissue culture, photosynthetic photon flux density (PPFD: Photosynthetic Photon Flux Density), photoperiod and spectral distribution play an important role in plant photosynthesis and morphogenesis. Plant tissue culture mainly relies on electric light source. The traditional electric light source has extremely low bio-efficiency and high calorific value for plants, and light electricity accounts for about 65% of the total electricity cost. It is one of the highest non-labor costs in plant tissue culture. Therefore, using LED to provide illumination in plant tissue culture, regulating light quality and PPFD can not only regulate the growth and morphogenesis of tissue culture plants, shorten the culture period, improve the quality, but also greatly reduce energy consumption and reduce costs.

(1) Effects of red light (620-660 nm) and far red light (710-740 nm) LED on the growth of tissue culture plants

The ratio of red light to far red light flux (R/FR) in the spectrum has an important influence on plant morphogenesis and plant height adjustment. The R/FR ratio has become an important evaluation parameter for controlling plant morphology.

Fujiwara and other research found that among the LED light sources, red LEDs and far red LED light sources are more likely to affect the light form formation and growth of tissue culture seedlings than fluorescent lamps. Tanaka et al. found that red LED promoted leaf growth of orchid tissue culture seedlings but reduced chlorophyll content, stem and root dry weight. Lian et al. showed that under the irradiation of red LED alone, the growth index and dry matter accumulation of lily bulbs were lower, which was related to the low CO2 assimilation caused by red light alone. This result confirms the results of Goins et al.'s research on the application of red LEDs to wheat photosynthetic yield.

However, reports of the effects of red or far-red LEDs on the growth of tissue culture plants are not consistent. Miyashita et al. found that with the increase of PPFD of red LEDs, the stems of potato tissue cultured stems increased, and the chlorophyll content also increased, but there was no significant difference in leaf area and dry weight. Nhut et al. showed that under the irradiation of red LED, strawberry tissue cultured leaves stretched, petiole elongation, stem elongation, but chlorophyll content decreased. According to Kim et al., under the treatment of single red LED or red LED + far red LED, excessive elongation of chrysanthemum tissue culture stems leads to fragile stems, and other important growth indicators are also reduced, which is generally not conducive to the normal growth and development of plants. . Hahn et al. found the inhibitory effect of red LED on the stem growth of the tissue culture seedlings. These phenomena are believed to be that monochromatic red light causes an imbalance in the distribution of light energy available to photosystems I and II, thus inhibiting stem growth.

In addition, in the experimental results of different light quality LEDs with PPFD of 45 μmol/(m2·s) for the treatment of orchid protocorm small pieces, it was found that red LED treatment is the most induced callus from protocorm segments. Effective.

(2) Effect of blue light (450 ~ 470 nm) LED on the growth of tissue culture plants

It has been reported that blue light directly or indirectly affects plant embryonic axis elongation, enzyme regulation and synthesis, stomatal opening, chloroplast maturation and photomorphogenesis. However, reports on the single blue LED significantly affecting the growth and development of tissue culture seedlings are rare.

Appelgen et al. reported that blue light strongly inhibited the elongation of stems of geranium tissue culture seedlings. Nhut et al. showed that the number of leaves of strawberry tissue cultured plants treated with a single blue LED was the least, and the root length was the shortest, which inhibited the growth of strawberry tissue culture seedlings. However, no blue LED irradiation caused the growth and development imbalance of strawberry tissue culture seedlings.

In the study on the growth effect of the photosynthetic characteristics of calla seedlings, there was no significant difference in dry mass and growth rate before LED treatment, but the addition of blue LED treatment had significant positive effects on chlorophyll content and plant height index. effect. Tanaka et al. found that red LEDs promoted the growth of orchid leaves but reduced the content of chlorophyll, while blue LEDs reversed this effect.

(3) Effect of combination of red and blue LED on tissue growth of tissue culture

So far, there have been many reports that the red-blue LED combination has a positive impact on the growth and development of tissue culture plants, which is superior to monochromatic light treatment. For example, Hahn et al. found that the seedlings of Foxglove plant treated with a single red LED or blue LED showed a long-lasting phenomenon, but grew robust under the red-blue LED composite light. It has also been found that a double-Butterfly tissue culture plant has the best rooting under the red LED, and the rooting is the worst under the blue LED; and under the red and blue LED composite illumination, the root number, fresh weight and chlorophyll content of the plant are comprehensive. The indicator is significantly better than monochrome LED and fluorescent lamp processing.

Studies have shown that red and blue LED combinations can increase plant photosynthetic rate to increase plant growth and development because the spectral energy distribution of red and blue light is consistent with the chlorophyll absorption spectrum. Kim et al. found that the photosynthetic rate of chrysanthemum tissue cultured under red and blue LED composite light was the highest, the fresh quality, dry mass and leaf area were the largest, the number of pores was the least, and the stomatal opening was the largest. Tanaka et al reported that the fresh weight and dry weight of orchid tissue culture seedlings irradiated by red and blue LED composite light increased. Lian et al. experimented on the in vitro cultured bulbs of lily. The red and blue LED composite light is more suitable for the growth of bulbs. The size, fresh, dry quality and root number of bulbs are the highest.

However, the results of the research on the red-blue LED combination and the research of different tissue culture plants as experimental materials are not consistent. For example, Nhut et al. used 80% red LED + 20% blue LED combination to promote the growth and domestication of banana seedlings. A study on eucalyptus tissue culture seedlings found that the same red and blue LED ratio, combined with gas permeable membrane and rock wool substrate, can achieve its sugar-free culture. After Nhut et al., it was found that under the irradiation of 70% red LED + 30% blue LED, the number of leaves, root number, root length, fresh weight and dry weight of strawberry tissue culture seedlings were the highest, and the growth of transplanted into soil was also the best. Subsequent studies on the tissue culture seedlings of Baihejing have also yielded similar results. It can be seen that different plants have different sensitivities to the light quality ratio and exhibit different adaptability.

In the results of the fresh/dry mass accumulation index of potato tissue culture seedlings, it was found that the synergistic illumination control was better than the alternate intermittent illumination control, and the growth effect of 45% red LED + 55% blue LED on the potato tissue culture seedlings It is the best. In addition, studies have found that under the combination of 25% red light + 75% blue LED, the highest incidence of protocorm bodies can be obtained from the callus induced from the orchid bulbs.

3, LED used in facilities gardening

In the past ten or twenty years, the horticultural area of ​​China's facilities has developed rapidly, and the light environment control lighting technology of plant growth has attracted attention. Facilities Horticultural lighting technology is mainly used in two aspects: first, as a supplemental illumination for plant photosynthesis when the amount of sunshine is small or when the sunshine time is short; second, it is induced illumination as a plant photoperiod and light form.

(1) LED as a supplemental illumination for plant photosynthesis

Nichols and other studies have found that traditional artificial light sources in greenhouses generate too much heat. For example, LED supplemental lighting and hydroponic systems can be used to recycle air. Excessive heat and moisture can be removed and energy can be efficiently converted into effective Photosynthetic radiation is ultimately converted to plant matter. With a 400 ms frequency and a 50% duty cycle, the growth rate and photosynthetic rate of lettuce increased by more than 20%. This study shows that it is feasible to use LEDs in plant factories.

Yanagi et al. found that compared with fluorescent lamps, the effect of red LED on spinach growth was not obvious. After adding blue LED, the growth morphology of spinach was significantly improved. Yorio and other research found that the application of 90% red LED + 10% blue LED as supplementary lighting can significantly promote the growth and development of spinach, radish and lettuce. Shin et al. found that the growth of sugar beet under red light and blue LED was the largest, and the accumulation of betaine in hair roots was the most significant, and the highest sugar and starch accumulation in hair roots.

It has been reported that the anatomical morphology of pepper stems and leaves grown under the combined illumination of red and blue LEDs is significantly different from that of the control metal halide lamps. The study by Choi et al. has similar conclusions. The anatomical characteristics of the stems and leaves of perilla growing under the combined illumination of red and blue LEDs are significantly different from those of perilla grown under metal halide lamps, and with the increase of PPFD, perilla The photosynthetic rate is increased. Heo observed the microstructure of marigold and sage, and found that the number of stomata of the two plants increased under the combined illumination of red and blue LEDs compared to the monochromatic blue or red LED.

(2) LED as induced light for plant photoperiod and light form

Goins and other studies have found that red LEDs can delay the flowering time of Arabidopsis. Heo et al. found that red light + blue LED induced the flowering of cyclamen. The flower bud number and flowering number were the highest under 10h photoperiod treatment. The single red or blue LED illumination reduced the flowering reaction and regulated the length of the peduncle. Flowering period is conducive to cut flower production and marketing. It can be seen that the flowering and subsequent growth of the plants can be regulated by the light quality and photoperiod.

Heo and other research results show that under the illumination of fluorescent lamp + blue LED, fluorescent lamp + red LED, fluorescent lamp + far red LED, there is no significant difference in the dry quality of musk scent; fluorescent lamp and fluorescent lamp + red LED light treatment, musk 蓟 and There is no significant difference in plant height of marigold, but the two plants under fluorescent light + far red light treatment have the highest height; compared with single fluorescent lamp treatment, fluorescent light + red LED and fluorescent light + far red LED composite light treatment significantly improve marigold stomata quantity.

4, LED applied to the space ecological life insurance system

At present, it is generally believed in the international community that the establishment of a controlled ecological life support system (CELSS) is the fundamental way to solve the problem of long-term manned space life support. One of the key technologies to establish this system is to solve the higher plant cultivation techniques. One of the key issues involved in the cultivation of higher plants in space is the lighting technology.

Based on the special requirements of the space environment, the light source used in the cultivation of higher space plants must have high luminous efficiency, and the output light wave is suitable for plant photosynthesis and morphogenesis, small size, light weight, long life, high safety and reliability record and no environment. Pollution and other characteristics. Therefore, in recent years, the application of light-emitting diodes in space plant cultivation has received much attention. The study found that both Xenon metal halide lamps and LED lighting systems can provide the spectral energy distribution and uniform illumination required by CELSS, but the lighting efficiency of LED lighting systems is more than 5 times that of Xenon metal halide lamps.

Guo Shuangsheng and other studies have found that the normal growth of space plants can use a certain combination of red and blue LEDs, with 90% red + 10% blue LED tube is more suitable. Kim and other studies found that 24% green + blue + red (RGB) treatment promoted the growth of lettuce, compared with the cold white fluorescent treatment group, the photosynthetic yield of lettuce in the RGB treatment group was significantly improved.

The 21st century will be the century of ecological agriculture, and physical agriculture is one of the main ways to realize ecological agriculture. In many physics subject knowledge, optics plays a vital role in it. Therefore, some scholars believe that "the century of light" "coming soon. How to control different artificial light sources to implement different "light fertilizers" for green plants under the condition of insufficient sun light, not only to promote crop growth and development, but also to achieve the purpose of increasing production, high efficiency, high quality, disease resistance and pollution-free, which promotes modern agriculture in China. The development has very important practical significance.