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Effect of LED on Plant Growth and Seedling Strength Index

by TUBU

February 1, 2024


The effect of LED red and blue continuous light on the growth and seedling growth index of chili pepper seedlings. In order to investigate the effects of continuous LED red and blue light on the growth and seedling growth index of chili peppers as a continuous light-tolerant plant, regular red and blue light (red:blue=4:1, 240 μmol-m-2-s-1, 18/6 h), continuous red and blue light (red:blue=4:1, 180 μmol-m-2-s-1, 24/0 h), continuous red light (red, 180 μmol-m-2-s-1, 24/0 h), and continuous red light (red, 180 μmol-m-2-s-1, 24/0 h) were used to control the growth of chili peppers in the plant plant. -2-s-1,24/0 h), continuous red light (red light, 180 μmol-m-2-s-1,24/0 h), and continuous blue light (blue light, 180 μmol-m-2-s-1,24/0 h). The seedlings were harvested at the 15th, 20th and 25th days of planting to compare the effects of different treatments on plant height, stem thickness, leaf area, specific leaf weight and seedling index of chili peppers. The results showed that in the early stage of planting, chili seedlings grew rapidly under continuous red light treatment, and their plant height, leaf area, aboveground fresh weight and total fresh weight were significantly higher than those of other treatments, but their specific leaf weight was low, leaf direction value was high, and the chili seedlings were poor in shape and low in light energy utilization. With the prolongation of planting time, the aboveground fresh weight and belowground fresh weight of chili seedlings under continuous blue light treatment were higher than those of other treatments, and the leaf orientation value of chili seedlings under continuous blue light treatment was the lowest, and the specific leaf weight and seedling index were the highest. In conclusion, under the same DLI conditions in this experiment, CL could promote the growth of chili pepper seedlings, in which the continuous blue light treatment had better growth and higher seedling index, and the treatment had the lowest leaf orientation value and the highest seedling value.

Vegetable production is an important part of agricultural production, which not only meets the needs of people's daily life, but also brings great economic benefits to vegetable farmers. Vegetable nursery is the first part of vegetable production, and the quality of seedlings is crucial to the yield and quality of vegetables after planting. Traditional seedling nurseries are affected by bad weather, and inevitably face many challenges such as slow seedling growth, stunted growth, pests and diseases. With the development of LED lighting technology, the use of artificial light for vegetable factory nursery has high nursery efficiency, less pests and diseases, easy to standardize and other traditional vegetable nursery methods are difficult to compare the advantages. A new generation of LED light source than the traditional light source with energy-saving and efficient, long life, environmental protection and durability, small size, low thermal radiation, wavelength amplitude is small, can be in the plant factory environment according to the needs of seedling growth and development of the development of the appropriate light formula, precise control of seedling physiological metabolic processes, to achieve the vegetable seedling of pollution-free, standardized and rapid production, shorten the cycle of seedling.

Individual plant seedlings are very sensitive to changes in the light environment, and the quality of the seedling stage is crucial for seedling nurseries. Plants have selective absorption of light spectrum, and different wavelengths of light can regulate physiological activities such as plant morphogenesis, photosynthesis and material metabolism. In recent years, the use of light quality to regulate the growth of vegetables has been widely concerned by scholars at home and abroad, and it has been shown that light quality has an important role in regulating the growth and development of horticultural crops, such as tomatoes, eggplants, cabbages, peppers and so on. Previous studies have shown that: blue light inhibits crop growth by reducing IAA levels in plants, red light promotes cotyledon elongation, but inhibits stem overgrowth; increasing the ratio of red light in the light environment improves the chlorophyll content of strawberry leaves, and increasing the ratio of blue-violet light improves the chlorophyll content of lettuce and tomato leaves, which is beneficial to crop photosynthetic production; red light increases leaf chlorophyll content by inhibiting photosynthetic output from leaves; red light increases leaf chlorophyll content by inhibiting leaf output from photosynthetics. Red light can increase the accumulation of starch in leaves by inhibiting the output of photosynthetic products from leaves.

Continuous light refers to the light environment that is different from the original 24h photoperiod of day and night in nature, and provides plants with continuous light and dark conditions for 24h. Continuous light prolongs the time of photosynthesis, and is another effective means to increase the input of light quanta and promote plant growth in plant factories in addition to strong light irradiation. It has been found that continuous light can accelerate plant growth, increase biomass and improve quality. As a photoperiod-insensitive crop, chili peppers can grow better under continuous light. Wu Genliang et al. used a combination of red and blue light and high light intensity to prolong the photoperiod to improve the growth of chili peppers. However, few studies have been conducted on continuous red and blue light for seedling production by utilizing the photoperiod insensitivity of pepper crops. Light intensity, light quality and photoperiod are interrelated and constrained in the light environment. In this experiment, different light quality and photoperiod treatments were used to investigate the effects of continuous red and blue light on seedling growth of chili peppers under the condition of maintaining the same amount of accumulated light in the present day.

LED red and blue light to cultivate chili peppers

Test materials and methods

Test materials

The test was conducted with SITC No.23 cow horn pepper as the test object,selecting full,uniformly sized and glossy seeds,and soaking them in warm water at 55℃for 15 min to disinfect them.After soaking,the seeds were taken out and washed,and soaked in water for 8 h.Lettuce seedling trays were used to spread 4 layers of gauze on the grid,and then the soaked seeds were evenly spread on the gauze,covered with 2 layers of gauze,and watered thoroughly with pure water.Inside the tray,50 ml of water was added to ensure a humid environment.Put the trays into a constant temperature incubator at 28℃and germinate under dark condition.Observe the germination situation every day and supplement water appropriately,and it is expected that the germination can be good in 4d.The ratio of seedling substrate was V(grass charcoal):V(vermiculite):V(perlite)=3:1:1.Nutrient solution was formulated using Hoagland nutrient solution,with the pH of the nutrient solution adjusted to 5.5~6.5 and the EC value adjusted to 1.5~1.8 mS/cm.Two varieties of chili peppers were planted in each treatment,and the same chili pepper was put into one hole tray with 72 holes,and the exterior dimensions of the tray were 540mm×280mm×280mm×280mm×280mm×280mm×280mm,and the exterior dimensions of the tray were 540mm×280mm×280mm×280mm×280mm×280mm.The specification of the hole tray was 72 holes,the appearance size was 540mm×280mm×40mm,the density was 476 plants/m2,the plant spacing was 4.5cm,and the hole trays were washed and dried before use.

When the seeds are "white", select uniform and healthy seeds and sow them into the hole tray with tweezers.

1. Before sowing, spread the mixed substrate evenly in the hole, the substrate is about 1cm from the upper surface, the substrate in each hole of the hole tray should be uniform, loose, and no hollow, and then use the "tidal" method to water the substrate thoroughly (all water is distilled water).

2. Gently sow 1 seed in each hole. When sowing, the seeds should be placed flat in the hole, not upright, to avoid the "cap" out of the soil.

3. Cover the hole tray with substrate after sowing, and use a scraper to scrape away the excess substrate above the hole grid, so that the hole grid is clearly visible. Then use the "tidal" method of watering. After watering, let the hole tray dry out for about 10 minutes so that the water in the substrate can run off.

4. Seal the holes of the hole tray with plastic wrap (or black cloth) (2d) to prevent rapid evaporation of water from the substrate (remove the plastic wrap when the first seedling is observed to emerge from the soil).

Experimental design

The experiment used LED red and blue light to cultivate chili peppers, and the DLI of all light treatments was equal, which was 15.552 mol/m2-d. The bright-phase period was from 16:00 to 10:00, and the dark-phase period was from 10:00 to 16:00. Treatment 1 was conventional light (RB-NL), with a light intensity of 240 μmol-m-2.s-1 during the bright-phase period, and a light quality of R:B=4:1 (red light:blue light=4:1, same below), and a light intensity of 0 μmol-m-2.s-1 during the dark-phase period. The light intensity was 240 μmol-m-2.s-1 in the bright period, and the light quality was R:B=4:1 (red:blue=4:1, hereinafter), while the light intensity in the dark period was 0 μmol-m-2.s-1. Treatment 2 was red-blue continuous light (RB-CL), and the light intensity and light quality were maintained at 180 μmol-m-2-s-1 and R:B=4:1, respectively. Treatment 3 was red-only continuous light (R-CL), and the light intensity was maintained at 180 μmol-m-2-s-1, and the light quality was R. Treatment 4 was pure red continuous light (R-CL), and the light intensity was maintained at 180 μmol-m-2-s-1, and the light quality was R. Treatment 4 was pure red continuous light (R-CL), and the light intensity was maintained at 180 μmol-m-2-s-1. Treatment 4 was pure blue light continuous illumination (B-CL), the light intensity was kept at 180 μmol-m-2-s-1, and the light quality was B.

Measurement items and methods

Destructive measurements were carried out at the 15th, 20th and 25th d after germination, respectively. Ten seedlings of each variety of chili pepper were randomly selected from the hole tray of each treatment group, rinsed with clean water, and the leaf orientation value (the angle between the petiole and the main stem) of the seedlings was determined with a protractor, the height of the seedlings was measured with a straightedge, the thickness of the seedlings' stems (the thickness of the stems in the lower 1/3 of the cotyledons) was measured with vernier calipers, and the masses of the aboveground and below-ground parts of the plants were weighed by an electronic balance, and the leaf areas were determined by a leaf area meter, and the seedling index was calculated. The seedling index was calculated by measuring the leaf area with a leaf area meter. Then, the total dry weight was weighed at 105℃ for 25min and then dried at 72℃ for 48h to constant weight. Specific leaf weight and seedling index were calculated as follows: specific leaf weight=total leaf weight/total leaf area; seedling index 1=(stem thickness/plant height×total dry weight)×10; seedling index 2=(stem thickness/plant height×total fresh weight)×10.

Data processing

Microsoft Excel 2010 and SPSS 23 software were used to process the data, and the data were analyzed by one-way analysis of variance (ANOVA) using ANOVA software, and multiple comparisons of significant differences (P<0.05) using Duncan's test, and plotted using Origin 2021 software.

Results and Analysis

Effects of co.ntinuous LED red and blue light on the growth pattern of chili pepper seedlings

During this experiment, the plant height of pepper seedlings in R-CL treatment was significantly higher than that of other treatments. At 15 d of planting, there was no significant difference in plant height among the three treatments except for R-CL. With the increase of planting days, the difference was gradually manifested, and at 25 d of planting, the plant height of B-CL treated chili peppers went through a period of rapid growth, and the plant height was second only to that of the R-CL treatment, followed by that of the RB-CL treatment, and the lowest was that of the RB-NL treatment. The differences in stem thickness among the different light treatments were relatively small. At 15 d, the stem thickness of R-CL treatment was significantly higher than that of other treatments. At 20 d, the treatments did not show significant differences, while at 25 d, the stem thickness of R-CL treatment was smaller than that of B-CL and RB-CL treatments, and the stem thickness of RB-NL treatment was the smallest.

Effects of continuous LED red and blue light on leaves of chili seedlings

Chili pepper leaf direction value and leaf area directly affect the plant shape and the utilization of light energy and the production potential of varieties. Under R-CL treatment, the leaf orientation value of chili pepper seedlings was significantly higher than other treatments, and its leaf area was also the highest, but its leaf weight was lower than that of B-CL treatment, and finally, through the analysis of variance (ANOVA), it was found that the specific leaf weight was significantly lower than that of other treatments under this treatment.The specific leaf weights of B-CL and RB-C1 were the highest, among which, under the treatment of B-CL, leaf orientation value was the lowest significantly, and the leaf weight was the highest significantly. It indicated that under B-C1 treatment, the light energy utilization of the leaves of pepper seedlings was the highest, and their plants were more utilized for later growth.

Effect of LED red and blue continuous light on dry and fresh weight of chili seedlings

It can be found that at 15d of planting, chili seedlings under R-CL treatment grew rapidly, and their aboveground fresh weight and total dry fresh weight were significantly higher than those of other treatments, and there was no difference between treatments except for the RB-NL treatment in the belowground part. With the prolongation of planting time, the growth of chili seedlings under R-C1 treatment slowed down compared with other treatments. At 25 d, the aboveground fresh weight, belowground fresh weight and total dry fresh weight of B-CL treatment were significantly higher than those of other treatments, while all the indexes of the RB-NL treatment were significantly lower than those of other treatments.

Effects of continuous LED red and blue light on seedling strength index of chili pepper seedlings

Seedling index 1 and 2 had small differences among the treatments in the early stage of planting of chili seedlings, and the differences among the treatments increased significantly with the prolongation of planting time. At 15d, seedling index 1 of chili pepper seedlings under B-CL treatment was the highest, while there was no significant difference among other treatments, and this result was similar to that of seedling index 2; at 25d, seedling index 1 of chili pepper seedlings, seedling index 1 of B-CL and RB-CL treatments were the highest, followed by RB-NL and R-CL, and the difference among treatments was more obvious in seedling index 2, in which the difference among treatments was significantly higher than that of the other treatments under B-CL treatment. The differences among treatments were more obvious in seedling index 2, in which the B-CL treatment was significantly higher than the other treatments, followed by RB-CL, RB-NL, and the R-CL treatment had the lowest seedling index 2.

Plant light application

Discussion

CL increases the duration of photosynthesis and assimilation in plants while avoiding the consumption of respiration during the dark period, thus increasing the accumulation of dry matter and nutrients.Kozai et al. demonstrated that CL significantly increased the dry weight, fresh weight and leaf area of tomato.Zha et al. showed that the aboveground dry and fresh weights of lettuce were higher in CL compared with the normal photoperiod treatment at the same light intensity and the increase of biomass was dependent on specific leaf weight rather than leaf area, which significantly promoted the growth of lettuce seedlings.The results showed that the aboveground dry and fresh weights were higher in CL compared with the normal photoperiod treatment at the same light intensity. The increase in biomass was dependent on specific leaf weight rather than leaf area, which significantly promoted the growth of lettuce seedlings. In this study, we showed that continuous light was effective in promoting the biomass accumulation of chili peppers at the seedling stage compared with conventional light.

Jishi et al. determined the effect of LED red and blue light staggered irradiation on lettuce growth, and found that under the same conditions of DLI, lettuce leaves became longer and yield increased as the irradiation time of monochromatic blue light increased. In this study, the aboveground fresh weight, belowground fresh weight, specific leaf weight and seedling index of chili pepper seedlings were significantly higher than those of other treatments under continuous blue light irradiation, and the leaf orientation value was significantly lower than those of other treatments. The leaf orientation value is a comprehensive index that can simultaneously respond to the two characteristics of leaf "straight" and "vertical". The small leaf orientation value resulted in the upward extension of the leaf surface and the small space occupied by the whole plant, which was more conducive to the utilization of light energy and inter-plant ventilation. Pu Gaobin and other research found that the seedling irradiation of blue light can also promote the growth of tomato seedlings, is conducive to the cultivation of strong seedlings, and that blue light irradiation of tomato seedlings photosynthetic rate is significantly higher than the control, which may be due to the blue light to promote the opening of the stomata of the leaves, increasing the concentration of inter-cellular CO2; Bai Shengwen and other research on the impact of blue and purple light on the growth and physiology of chili peppers, the experimental found that the blue light treatment of plant height, dry weight, fresh weight, It was found that the plant height, dry weight, fresh weight, photosynthetic rate and stomatal conductance increased significantly under blue light treatment, and the dry weight and photosynthetic rate of the plants were more than twice as high as those under white light treatment. Yang Zhenchao et al. also found that in the treatment group with a higher proportion of blue light, the photosynthetic performance of chili pepper seedlings was significantly improved, which was more conducive to the growth in the plant factory environment.

In conclusion, continuous light promoted the biomass accumulation of chili seedlings, in which the plant height increased significantly under continuous red light treatment, the total dry weight, total fresh weight, seedling index and specific leaf weight increased significantly under continuous blue light treatment, and the lower leaf orientation values indicated that the chili seedlings were better shaped under the continuous blue light treatment, which was more conducive to the plant factory nursery.

About the author

TUBU is an expert in LED light research with more than 10 years of experience in this field. We hope that through our TUBU research, LED lighting technology will become more popular and bring greater convenience and comfort to people's lives.

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