Going to the season of eating strawberries! What are the effects of different LED light sources on strawberries?

It’s time to pick strawberries and eat strawberries! For the food, it is delicious and red like strawberry, I can't wait to eat it all the year round. How to resist the cause of the gas, can not be achieved. To this end, eat goods should seriously study this article, maybe you can grow strawberries yourself.

The growth and development of plants is affected by the external environment (such as light, temperature, gravity, moisture and minerals), and is most affected by light. Light intensity directly affects the growth and structural characteristics of plants; photoperiod mainly affects flowering and flowering differentiation of plants; and the effect of light quality on plants is more important and complex, not only as energy regulation and photosynthesis, including visible light Plant stomatal movement, leaf growth, chloroplast structure, photosynthetic pigments, photosynthetic carbon assimilation, etc., also act as trigger signals to affect plant growth. Different light qualities trigger different photoreceptors, which affect the photosynthetic characteristics, growth and development, stress resistance and senescence of plants. Studies have shown that blue light affects plant phototropism, photomorphogenesis, stomatal opening and photosynthesis, which can reduce the level of auxin (IAA) in plants and inhibit growth; while red light can promote plant cotyledon elongation and inhibit stem overgrowth. Growing. In addition, light also has a greater impact on the nutrient content of plants. Studies have found that red light can significantly increase the soluble sugar content of leaf lettuce, radish sprouts, cucumber, pepper and tomato seedlings; blue light can increase the anthocyanin content of tomato; and suitable red and blue light can promote lettuce seedlings The accumulation of nutritional quality of carbohydrates and cherry tomatoes increased the ascorbic acid content of leaf lettuce and Komatsu, and reduced the nitrate content of leaf lettuce.

The light environment is the most important environmental factor in facility cultivation, and it has a wide range of regulation effects on plant morphogenesis, photosynthetic characteristics, physiological metabolism, yield and quality. The use of light quality to control plant morphogenesis and growth is an important technology in the field of greenhouse cultivation. As the most promising and promising artificial light source in the field of future facilities, LED light source is widely used in plant growth research because of its long life, pure spectrum and low energy consumption. At present, the research on strawberry mainly focuses on light intensity, temperature, cultivation method, mineral nutrition and post-harvest storage. However, most of the research on light quality of strawberry adopts filter film with similar solar light transmittance, which cannot be accurately quantitatively modulated. Spectral energy distribution, light quantity unit and light intensity are not uniform, which affects the accuracy of its research. In this paper, the quality of single-wavelength light was obtained by using LED precision modulated light quality, and the effects on photosynthetic characteristics and yield and quality of strawberry were studied in order to provide scientific reference for the regulation of light quality environment of strawberry in facility cultivation.

Materials and Methods

Test material and experimental design

The experiment was conducted in September 2013-May 2014 at the Science and Technology Innovation Park and Artificial Climate Room of Shandong Agricultural University. The strawberry (Fragaria ananassa) variety was “Miaoxiang No.7” and was purchased from the College of Horticulture Science and Engineering of Shandong Agricultural University. The experiment consisted of 5 treatments: red, blue, yellow, red/blue/yellow (7/2/1, number of lamps of different colors), red/blue (7/2), with white light as a control. On September 20, 2013, a robust and consistent three-leaf seedling was selected and transplanted into a hard plastic pot containing a seedling substrate, and placed under a climate indoor LED light source. Six pots of strawberry were planted per pot. 6 pots. The nutrient solution is based on the Japanese Yamazaki formula (strawberry) and is replaced every 7 days. Other management methods are the same as usual.

The LED light source is provided by Guangdong Chunying Optoelectronics Technology Co., Ltd. The light culture frame is a steel frame structure, the light source is placed on the top, and the outer layer of the culture frame is a silver shade cloth to ensure that the LED light source is the only light source for plant growth. The distance between the strawberry plant and the light source is adjustable, the modulated light intensity is 500μmol·m2·s, the daytime temperature in the controlled climate room is 15～22°C, and the nighttime is 10～13°C. The illumination time of each treatment starts from 7:00 and is controlled by the timer. Light 12h·d.

Measurement items and methods

Five plants were randomly selected, and the leaf photosynthetic parameters (Pn, Tr, Gs, and Ci) were determined by CIRAS-1 photosynthetic apparatus. The mature leaves were selected at 9:00-10:00 on November 20, 2013, and the light intensity was measured. 500μmol·m2·s, leaf temperature 18～20°C, external CO2 concentration 480μmol·mol; chlorophyll fluorescence parameters were measured by FMS-2 portable pulse modulation fluorometer, on November 22, 2013 9:00-10: 30 Determination, fluorescence parameters were measured in the same leaves: initial fluorescence (Fo), variable fluorescence (Fv), steady-state fluorescence (Fs), maximum fluorescence (Fm), dark adaptation 30 min, PSII maximum photochemical efficiency (Fv/Fm) Actual photochemical efficiency of PSII (ΦPSII); the leaf pigment content was measured on the 30th, 40th, 50th, 60th and 70th day of illumination, using 80% acetone colorimetric method; the fresh quality of strawberry fruit was weighed by MP200B electronic balance; The content of soluble solids was determined by refractometer; the total acid content was determined by acid-base titration; the content of vitamin C and protein was determined by 2,6-dichlorophenol phenol colorimetry and Coomassie brilliant blue method, respectively. Five strains were randomly selected for each treatment, and three replicates were performed.

data processing

The data were statistically analyzed using DPS7.05 and Excel2003 software, and the variance was tested by the multiple comparison Duncan new complex range method (α=0.05). Drawing with Excel2003 software. The data in the graph is the mean ± standard deviation.

results and analysis

Effects of Light Quality on Photosynthetic Characteristics of Strawberry Leaves

It can be seen from Table 1 that different light quality treatments have significant effects on the photosynthetic characteristics of strawberry leaves, and the effects on net photosynthetic rate and transpiration rate are consistent, which are the highest under red light treatment, which are 49.3% and 37.6% higher than the control, respectively. The remaining effects were red/blue/yellow (7/2/1)>red/blue (7/2)>white light>yellow light; the smallest under blue light, which was 50.2% and 27.3% lower than the control, respectively. Compared with the control, all the treatments increased the stomatal conductance of the leaves, and the blue light treatment effect was the most significant, which was 31.2% higher than that of the control. The intercellular CO2 concentration was the highest in blue light, followed by yellow, red, red/blue (7/2), red/blue/yellow (7/2/1), and white light.

Effects of Light Quality on the Fluorescence Characteristics of Strawberry Leaves

Fo and Fm respectively indicate the fluorescence yield of the photosystem II (PSII) reaction center when it is completely open and completely closed, both reaching the maximum under red light and the smallest under red/blue/yellow (7/2/1). The effect of ΦPSII is red light > white light > yellow light > blue light ≥ red / blue / yellow (7 / 2 / 1) ≥ red / blue (7 / 2). Fv/Fm reflects the maximum light energy conversion efficiency of the PSII reaction center, which is the largest under the treatment of red/blue/yellow (7/2/1), which is 41.4% higher than the control; the smallest under blue light, which is 29.3% lower than the control. Different light quality treatments Fv/Fo and Fm/Fo have similar trends, both red/blue/yellow (7/2/1)>red/blue (7/2)>red light>blue light>white light>yellow light .

Effect of Light Quality on Photosynthetic Pigment Content in Strawberry Leaves

Photosynthetic pigments are an important material basis for photosynthesis in plants. It can be seen from Fig. 1 that the photosynthetic pigment content of strawberry leaves increased first and then decreased with the extension of illumination time, reached the maximum at 50d, and the effect of different light quality treatment on pigment content was significant. Red/blue/yellow (7/2/1) treatment of chlorophyll a, chlorophyll b, carotenoids and chlorophyll (a+b) was significantly higher than other treatments, while blue light treatment and pigment content were significantly lower than other treatments. The content of chlorophyll a and carotenoids in red light treatment was not significantly different from that in the control, and the content of chlorophyll b and chlorophyll (a+b) was higher than that of the control. The content of chlorophyll a in red/blue (7/2) treatment was lower than that in the control, and the content of chlorophyll b was higher than that in the control, while the content of carotenoid and chlorophyll (a+b) was not significantly different from the control. Except for chlorophyll b, the yellow pigment treatment pigment content was higher than the control.

I: Red Light Redlight; II: Blue Light Bluelight; III: Yellow Light Yellowlight; IV: Red/Blue/Yellow (7/2/1) Red/blue/yellow (7/2/1); V: Red/Blue ( 7/2) Red/blue (7/2); VI: Whitelight Whitelight. Different lowercase letters indicate significant difference (P<0.05)

Effect of Light Quality on Yield of Strawberry Fruit

It can be seen from Table 3 that the effects of different light quality treatments on strawberry fruit yield are significant. The average fruit quality, maximum fruit quality, fruit per plant and yield of red/blue/yellow (7/2/1) treatments were significantly higher than other treatments, which were 8.3%, 77.3%, 10.0%, 17.8 higher than the control, respectively. %; followed by white light, the smallest under yellow light, which was 37.3%, 43.0%, 33.3%, and 56.1% lower than the control, respectively. The yield indexes of red light, blue light and red/blue (7/2) treatment were lower than the control. Among them, the average fruit quality of blue light treatment was small but the number of fruits per plant was large. It can be seen that the combination treatment of red/blue/yellow (7/2/1) can significantly increase the yield of strawberry fruit.

Effect of Light Quality on the Quality of Strawberry Fruit

Different light quality can regulate the soluble solids, titratable acid, vitamin C and protein content of strawberry fruit, and regulate the sugar and acid metabolism of fruit by regulating light quality. As can be seen from Table 4, the red light treatment of soluble solids content is significantly higher than other treatments, while the protein content is significantly lower than other treatments. The blue light treatment has the highest titratable acid and protein content. The content of vitamin C was consistent with the change of soluble solid content, which were red light> red/blue/yellow (7/2/1)> yellow light> white light> blue light> red/blue (7/2). The quality indexes of red/blue (7/2) treated fruits were lower, and the ratio of solid acid in red/blue/yellow (7/2/1) treated fruits was the highest, indicating that red, blue and yellow mixed light is most beneficial to improve fruits. The flavor quality.

Effect of Light Quality on Root Activity of Strawberry

It can be seen from Fig. 2 that the effects of different light qualities on the root activity of strawberry are red/blue/yellow (7/2/1)>white light>red light>yellow>red/blue (7/2)>blue light, There was no significant difference between red and white light, red/blue/yellow (7/2/1) increased by 10.0% compared to the control, while blue light decreased by 44.9% compared to the control. It can be seen that both monochromatic light and red/blue (7/2) are not conducive to improving the root activity of strawberry, and red/blue/yellow (7/2/1) can significantly improve the root activity of strawberry.

discuss

Photosynthesis, as the most important chemical reaction on earth, is the basis for the survival of all living things, and the driving force behind photosynthesis. Among the visible light used by plants, red and orange light are the most absorbed by chlorophyll. Secondly, blue and violet light can be strongly absorbed by chlorophyll and carotene. Only green light is rarely absorbed and utilized in photosynthesis. The spectrum affects the structure and characteristics of the leaf pores and plays an important role in regulating the stomatal opening and closing of crops. Studies have shown that different spectra can induce chloroplasts, cryptochromes and phytochromes of guard cells in leaves, thereby sensing different light components to adjust the pore size, which in turn affects stomatal conductance. The stomata are both the inlet for CO2 absorption by photosynthesis and the outlet of water vapor for the leaves, so the stomatal conductance has an important influence on the transpiration rate and photosynthetic rate of the crop. In this study, the photosynthetic rate of leaves was consistent with the trend of transpiration rate, which was dominated by red light, followed by red, blue, yellow and red and blue. The blue light treatment was the smallest, which was related to the light quality of Wusuo and green garlic. Consistently, it indicates that red light can promote photosynthesis of plants, which may be due to the fact that red light can regulate the assembly of photosynthetic apparatus at the transcriptional level, thereby promoting the absorption and transformation of light quality by crops. However, the stomatal conductance and intercellular CO2 concentration in blue light treatment are higher, presumably because a special blue light receptor (zeaxanthin) exists in the chloroplast, which makes blue light have higher quantum efficiency in promoting stomatal opening, but its photosynthetic rate. Lower, which means that the change of photosynthetic rate is not caused by the change of stomatal conductance, but by non-porosity factor, and the maximum light energy conversion efficiency (Fv/Fm) is reduced under blue light, indicating that the non-stomatal factor is blue light. Photoinhibition occurs underneath, resulting in a decrease in photosynthetic rate.

The chlorophyll fluorescence parameters are used to describe the photosynthesis mechanism and photosynthetic physiological status of plants, reflecting the "intrinsic" characteristics of plants. The intrinsic probes Fo and Fm, which are considered to study the relationship between plant photosynthesis and environment, respectively represent the photosystem II (PSII) reaction center. Fluorescence yield at full open and closed, where Fm reflects the electron transfer through the PSII. In this study, Fo and Fm were significantly higher in red light treatment than in other treatments, indicating that red light is beneficial to PSII electron transport and increases the fluorescence yield of strawberry. Fv/Fm reflects the maximum light energy conversion efficiency of the PSII reaction center, also known as the internal photochemical efficiency, and can be used as an indicator of photoinhibition. Studies have found that red and blue mixed light treatment can significantly increase the Fv/Fm value of leaf lettuce, green garlic seedlings and grape seedlings. In this study, the mixed light treatment Fv/Fm of red, blue, yellow and red and blue was significantly higher than other treatments, indicating that the PSII reaction center of the mixed light treatment blade was more open, and the light energy absorbed and used for photosynthesis was more. The maximum light energy conversion efficiency (Fv/Fm) under blue light is the lowest, indicating that blue light causes photoinhibition of PSII, which is a non-stomatal factor that causes a decrease in photosynthetic rate, resulting in a decrease in photosynthesis. In addition, ΦPSII reflects the actual photochemical efficiency of PSII under steady-state light intensity, which is commonly used to represent the quantum yield of plant photosynthesis electron transfer. High ΦPSII is beneficial to improve the light energy conversion efficiency of plants and accumulate more carbon assimilation for dark reaction. energy of.

In this study, the trend of monochromatic light treatment of ΦPSII was consistent with the change of net photosynthetic rate, indicating that ΦPSII has a good correlation with photosynthetic rate under non-adversity conditions. The change trend of ΦPSII and net photosynthetic rate under mixed light is opposite, indicating that the action mechanism of mixed light is not just a superposition, and there may be other effects.

Chlorophyll and carotenoids act as photosynthetic pigments of higher plants and play a very important role in photosynthesis of plants. Chlorophyll mainly plays the role of absorbing and utilizing light energy, while carotenoids contain chlorophyll-free in addition to collecting and transmitting light energy. A feature that is damaged by unwanted light.

Light stimulates leaf expansion and mesophyll cell differentiation while promoting the transformation of protoplasts or yellow bodies into chloroplasts. For most crops, red light is good for increasing chlorophyll content, while blue light reduces its content. Some studies have pointed out that the chlorophyll content of the leaves of the tomato seedlings treated with the red fluorescent lamp is the highest, and the blue light is the lowest; while the blue LED treatment can significantly increase the chlorophyll content of the lettuce leaves of lettuce and Jiangxin 14; the leaves of the Israeli rainbow and the Dutch red tomato The chlorophyll content is the largest with yellow LED treatment. In this study, the photosynthetic pigment content of strawberry leaves was highest in red/blue/yellow (7/2/1) and lowest in blue light treatment. It can be seen that there are large differences in the response of different vegetable types and varieties to the chlorophyll content of supplemental light treatment, which may be related to the different conditions for the realization of light quality. At the same time, the increase of pigment content is conducive to increase the photosynthetic rate, and the early nutrient growth is strong, which lays a foundation for the later increase of yield.

Fruit yield is related to many factors, and different light quality has a significant impact on different crop yields. Some studies have found that supplemental red light has the best effect on increasing yield of overwintering tomato; supplementing blue light can increase the number and total yield of cucumber fruit in greenhouse. The fruit size is thought to be related to the seeds in the fruit. The seeds contain a variety of endogenous hormones, such as auxin, gibberellin, cytokinins, etc., which may be involved in regulating fruit cell division and cell expansion, and light quality can make each The content and proportion of biological hormones change, which affects the size of the fruit. For strawberries, the time of flower bud differentiation is good, the quantity and quality are the main factors affecting yield. Flower bud differentiation refers to the process of plant transformation from vegetative growth to reproductive growth. In this study, red/blue/yellow mixed light treatment significantly improved fruit quality, number of results per plant and yield, indicating that chlorophyll content was high under mixed light, and the net photosynthetic rate was higher to provide sufficient photosynthetic products for flowering, thereby improving The quantity and quality of flower bud differentiation ultimately increases strawberry yield. At present, there is little understanding of the formation of strawberry flower buds by light quality, and its related mechanism needs further study.

Different light qualities have a greater regulation effect on fruit quality, and can regulate sugar and acid metabolism of fruits by regulating light quality. The mechanism of action of light on soluble sugar may be due to the absorption of carbohydrates by different light quality, which may change the soluble sugar content. It may also be that the change of light quality induces the regulation of sucrose metabolism enzyme by phytochrome and promotes sucrose metabolism. The activity of the relevant enzyme is increased, thereby accumulating more photosynthesis products. Some studies have found that red light can increase the sugar content of tomato, low dose UV-B combined with red light can increase the sugar, acid and lycopene content of the fruit; blue light treatment can significantly increase the vitamin C and soluble protein content of tomato fruit. The study found that red light treatment of soluble solids and vitamin C content were higher than other treatments, while blue light treatment significantly increased the content of protein and titratable acid.

It indicates that red light is conducive to the synthesis of carbohydrates, while blue light promotes the accumulation of proteins and organic acids. The effect of light quality on vitamin C is related to its synthetic enzyme activity. Galactose lactone dehydrogenase (GalLDH) is the last step of the vitamin C synthesis pathway, directly catalyzing the synthesis of vitamin C by galactosalactone; ascorbate oxidase (AAO) and ascorbate peroxidase (AAP) are oxidized vitamins in plants. The key enzymes of C, O2 and H2O2, respectively, oxidize vitamin C to unstable monodehydroascorbic acid (MDHA); all three enzymes are sensitive to light, but the specific effects of light on three enzyme activities are not yet clear. Studies have shown that the content of vitamin C in the fruit of Wenzhou mandarin orange is significantly positively correlated with the sugar content. The content of vitamin C in young leaves and mature leaves of spinach under white light is higher than that in dark light, because white light effectively improves the photosynthetic capacity of postharvest spinach leaves. Soluble carbohydrate content, especially glucose. This is consistent with the trend of soluble solids and vitamin C in this study. The reason may be that light quality can increase vitamin C content by increasing soluble carbohydrate content.

Root system is the main absorption organ of crops. The level of root activity directly affects the absorption and transfer of water, mineral elements and other nutrients, which in turn affects the conversion of substances and energy in plants. Light affects the growth and function of roots by affecting the photosynthesis of crops and the synthesis and transport of photosynthetic products. Yan Mengmeng and other studies found that red light significantly promoted the root growth of peanut seedlings and increased root activity, while blue light and yellow light significantly inhibited root growth; Pu Gaobin and other studies found that blue light can significantly improve the root activity of tomato seedlings; Guo Yinsheng and other studies found that red Blue combined light significantly increased the root activity of rice seedlings. In this study, the root activity of red/blue/yellow mixed light treatment was higher than that of red light and the lowest under blue light, indicating that the effect of light quality on root growth of different crops was different. In addition, the root system is used as a reservoir for the above-ground photosynthesis product, and its morphological construction and functional maintenance require the maintenance of photosynthetic products. At the same time, the maintenance and function of the photosynthetic organs require the participation of minerals and water absorbed by the roots. Studies have shown that there is a significant positive correlation between root vigor and photosynthetic rate and between root vigor and crop yield. This study also confirmed this point, under the red/blue/yellow mixed light treatment, the root activity increased with the increase of leaf photosynthetic rate, and the yield increased. It can be seen that root activity is closely related to the photosynthetic rate interaction of shoots.

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