Plant growth regulator and method for improving symbiotic nitrogen fixation under low light

Abstract

The application discloses a plant growth regulator. By externally applying the plant growth regulator to leguminous plants, the leguminous plants can maintain high tolerance under weak light conditions such as dense planting, strip complex planting, under forest, facility greenhouse or cloudy and rainy days, and the implementation is simple, labor is saved, and the plant growth regulator can be used for mechanical operation.

Description

Technical Field

[0001] This invention belongs to the field of biotechnology, and specifically relates to a plant growth regulator and a method and application of using it to improve symbiotic nitrogen fixation in legumes under low light conditions. Background Technology

[0002] Nitrogen is a macronutrient essential for plant growth and development; however, its content in soil is extremely limited. Although 78.1% of N2 exists in the Earth's atmosphere, the vast majority of plants cannot utilize this form of nitrogen. Legumes and rhizobia, as a symbiotic organism capable of recognizing each other and forming root nodules, can reduce atmospheric nitrogen to ammonia, which can then be absorbed and utilized by the plant. This symbiotic nitrogen fixation is the largest natural source of usable nitrogen for organisms in nature, and has a profound impact on the biomass and carbon deposition of agriculture and natural ecosystems. Furthermore, since nitrogen is a key limiting factor for plant growth and development, improving the efficiency of symbiotic nitrogen fixation is crucial for the growth and yield of legumes.

[0003] Symbiotic nitrogen fixation is an energy-intensive process, with the required materials and energy primarily derived from plant photosynthesis. Studies have shown that under low light conditions, plants experience reduced light capture and carbon assimilation capacity, mainly manifested as decreased leaf area index, chlorophyll content, and net photosynthetic rate. This leads to reduced dry matter accumulation in the aboveground parts, consequently failing to guarantee a sufficient carbon source for symbiotic nitrogen fixation and thus reducing nitrogen fixation efficiency. For soybeans, an important agricultural crop, low light causes a reduction in the number of effective pods, the number of seeds per unit, and the weight per seed, resulting in a significant decrease in soybean yield. Furthermore, light signals are a crucial switch for initiating symbiotic nitrogen fixation in legumes; under low light levels (comparable to forest understory), legumes completely shut down symbiotic nitrogen fixation. Therefore, sufficient light is a necessary condition for legumes to engage in symbiotic nitrogen fixation and growth.

[0004] Soybeans, as an important legume crop used for both grain and oil in my country, are often cultivated using dense planting, understory planting, and strip intercropping techniques to ensure yields under limited land space. For other legume vegetables such as kidney beans and peas, greenhouses and other facility agriculture technologies are frequently used to increase annual planting frequency and thus improve yields. However, since legumes are mostly light-loving crops, dense planting often results in mutual shading of leaves. Furthermore, when intercropped with other crops such as corn, soybeans are severely affected by the shade of tall corn stalks during their reproductive growth stage, placing them at a disadvantage in terms of light resources and causing a significant reduction in yield. Current technologies mainly alleviate this low-light stress problem through cultivation methods and supporting facilities, such as appropriately adjusting the plant spacing and using supplemental lighting in greenhouses, thereby minimizing the adverse effects of low light on plants. However, apart from regional light stress problems, under the background of natural conditions, light stress can occur anytime and anywhere with the continuous changes in climate. Conventional cultivation techniques cannot solve this problem. Therefore, there is an urgent need for an effective method and application to improve symbiotic nitrogen fixation in legumes under low light and reduce light damage. Summary of the Invention

[0005] In order to at least solve one of the technical problems existing in the prior art, the present invention provides a method for enhancing the photosynthetic intensity of leaves under low light conditions by using plant growth regulators, thereby improving the symbiotic nitrogen fixation of legumes. This method can effectively increase the chlorophyll content and nitrogen fixation efficiency of legumes under low light conditions, thereby mitigating the low light stress of plants and promoting the growth of legumes.

[0006] To achieve the above objectives, the present invention is implemented through the following scheme.

[0007] In a first aspect, the present invention provides a plant growth regulator, the plant growth regulator comprising humic acid, fulvic acid and / or 5-aminolevulinic acid (ALA).

[0008] In some embodiments, the humic acid is water-soluble humic acid.

[0009] In some embodiments, the fulvic acid is water-soluble fulvic acid.

[0010] In some embodiments, the humic acid and / or fulvic acid are obtained by microbial fermentation and degradation of lignite.

[0011] In some embodiments, the 5-aminolevulinic acid is obtained by microbial fermentation purification.

[0012] In some embodiments, the microorganism is Staphylococcus pasteurelli or Bacillus.

[0013] In some embodiments, the humic acid, fulvic acid, or 5-aminolevulinic acid may also be obtained by other means, including but not limited to commercially available products containing humic acid, fulvic acid, or 5-aminolevulinic acid.

[0014] In some embodiments, the humic acid is water-soluble and has a pH of 5-8, and its elemental composition contains 30%-70% carbon, preferably 40%-60%; 1%-6% hydrogen, preferably 2%-5%; 1%-5% nitrogen, preferably 2%-4%; 20%-60% oxygen, preferably 30%-50%; and 0.1%-5% sulfur, preferably 0.2%-3%.

[0015] In some embodiments, fulvic acid refers to a water-soluble humic acid product obtained through further purification, and its elemental composition comprises 30%-70% carbon, preferably 40%-60%; 1%-5% nitrogen, preferably 2%-4%; and 25%-65% oxygen, preferably 35%-50%.

[0016] In some embodiments, the plant growth regulator includes: 0.1–1.0 g / L humic acid, 0.05–0.50 g / L fulvic acid, and 0.03–0.10 g / L 5-aminolevulinic acid. Plant growth regulators exhibit dose-dependent effects when applied; therefore, higher concentrations may be detrimental to plant growth, while lower concentrations may have little effect.

[0017] In some implementations, humic acid, fulvic acid, and 5-aminolevulinic acid in the plant growth regulator are applied individually.

[0018] Secondly, the present invention provides a method for improving symbiotic nitrogen fixation in legumes under low light conditions, comprising the following steps:

[0019] When the legume seeds have grown to the point where the first pair of true leaves have opened, the seedlings are watered or sprayed with the plant growth regulator of this invention.

[0020] in,

[0021] Humic acid is applied by root irrigation, or

[0022] Fulvic acid is applied by foliar spraying, or

[0023] 5-Aminolevulinic acid is applied by foliar spraying.

[0024] In some implementation schemes, the concentration of humic acid used for irrigation is 0.1–1.0 g / L, with 5–15 ml per plant; or the concentration of fulvic acid used for spraying is 0.05–0.50 g / L, with 2–10 ml per plant; or the concentration of 5-aminolevulinic acid used for spraying is 0.03–0.10 g / L, with 2–10 ml per plant.

[0025] In some implementation schemes, irrigation or spraying is carried out every 4 to 7 days.

[0026] In some implementations, the legume seeds are surface-sterilized before cultivation. The surface sterilization involves placing the seeds in a container, adding anhydrous ethanol, gently shaking for 25-35 seconds, discarding the anhydrous ethanol, adding sodium hypochlorite solution, gently shaking for 4-6 minutes, discarding the sodium hypochlorite solution, and rinsing with sterile water 6-8 times.

[0027] In some implementations, the culture is performed in the dark at 26-30°C for 36-48 hours.

[0028] In some implementations, the low-light environment includes: densely planted areas, strip-shaped mixed planting areas, understory areas, greenhouse facilities, cloudy / rainy days, and light intensities ≤500 μmol / m². 2 / s environment.

[0029] Preferably, in the low-light environment, the light intensity is ≤500 μmol / m 2 / s, light intensity is 400umol / m 2 / s~500umol / m 2 / s, light intensity is 300umol / m 2 / s~400umol / m 2 / s, light intensity is 200umol / m 2 / s~300umol / m 2 / s, light intensity is 100umol / m 2 / s~200umol / m 2 / s, or light intensity ≤100umol / m 2 / s.

[0030] In some embodiments, the method of the present invention for improving symbiotic nitrogen fixation in legumes under low light conditions includes the following steps:

[0031] a. After sterilizing the surface of leguminous seeds, place them on a sterile water agar medium and incubate until germination;

[0032] b. Sow the germinated legume seeds in a flowerpot filled with vermiculite and soil;

[0033] c. Place the flowerpots in artificial climate chambers with different light intensities for 5-9 days;

[0034] d. When the first pair of true leaves of the seedlings open, water or spray the seedlings with the plant growth regulator of the present invention. Humic acid is applied by root watering, fulvic acid is applied by foliar spraying, or 5-aminolevulinic acid is applied by foliar spraying.

[0035] e. Place the treated plant seedlings in an artificial climate chamber and continue to grow for 21-25 days.

[0036] In some implementations, in step a, the surface disinfection involves placing the seeds in a container, adding anhydrous ethanol, gently shaking for 25-35 seconds, discarding the anhydrous ethanol, adding sodium hypochlorite solution, gently shaking for 4-6 minutes, discarding the sodium hypochlorite solution, and rinsing 6-8 times with sterile water.

[0037] In some implementations, in step a, the culture is performed in the dark at 26-30°C for 36-48 hours.

[0038] In some preferred embodiments, in step a, surface sterilization is required before seed germination. Specifically, the seeds are placed in a 500ml Erlenmeyer flask, 95% ethanol is added, and the flask is gently shaken for 30 seconds, then the anhydrous ethanol is discarded. A 1% sodium hypochlorite solution is then added, and the flask is gently shaken for 5 minutes, then the sodium hypochlorite solution is discarded. After rinsing 6-8 times with sterile water, the seeds are evenly placed on sterile 0.7% water agar medium and incubated in the dark at 28°C for 36-48 hours until germination. This treatment effectively removes oils and bacteria from the seed surface, softens the seed coat, improves germination efficiency, and promotes rapid seedling emergence.

[0039] In some implementations, in step b, the ratio of vermiculite to soil is 3:1.

[0040] In some implementations, in steps c and e, the environmental parameters of the artificial climate chamber are:

[0041] Under normal light, 510-600 umol / m 2 / s, humidity 45-55%, 14-16h; darkness, humidity 45-55%, 8-10h;

[0042] Low light intensity 100-150umol / m 2 / s, humidity 45-55%, 14-16h; darkness, humidity 45-55%, 8-10h.

[0043] In some implementation schemes, in step d, the watering / spraying is performed once every 4 to 7 days. Each watering treatment uses 5 to 15 ml of solution to water the plant roots, and each spraying treatment uses 2 to 10 ml of solution to spray on the leaves, so that it forms a surface mist on the leaves and just enough water droplets to fall.

[0044] In some preferred embodiments, in step d, the concentration of humic acid used for irrigation is 0.1–1.0 g / L, with 5–15 ml per plant; the concentration of fulvic acid used for spraying is 0.05–0.50 g / L, with 2–10 ml per plant, preferably 3–10 ml; and the concentration of 5-aminolevulinic acid used for spraying is 0.03–0.10 g / L, with 2–10 ml per plant, preferably 2–5 ml.

[0045] In some embodiments, the method of the present invention for improving symbiotic nitrogen fixation in legumes under low light conditions includes the following steps:

[0046] a. Select plump and undamaged legume seeds, disinfect their surfaces, and place them evenly on a sterile 0.7% water agar medium to incubate until germination.

[0047] b. Select legume seeds that germinate uniformly and sow them in flowerpots filled with vermiculite:soil = 3:1;

[0048] c. Place the potted plants in artificial climate chambers with different light intensities for 5 to 9 days;

[0049] d. When the first pair of true leaves of the seedlings open, water or spray the plant growth regulator of this invention onto the plants;

[0050] The concentration of humic acid used for irrigation is 0.1–1.0 g / L, with 5–15 ml per plant; the concentration of fulvic acid used for spraying is 0.05–0.50 g / L, with 3–10 ml per plant; and the concentration of 5-aminolevulinic acid used for spraying is 0.03–0.10 g / L, with 2–5 ml per plant.

[0051] e. Place the treated plant seedlings in an artificial climate chamber and continue to grow for 23 days.

[0052] After each treatment, the seedlings were placed in artificial climate chambers with different light intensities for cultivation. The environmental parameters were as follows:

[0053] 550umol / m under normal light 2 / s, 50% humidity, 16h; darkness, 50% humidity, 8h;

[0054] Low light intensity 100umol / m 2 / s, 50% humidity, 16h; darkness, 50% humidity, 8h.

[0055] Thirdly, the present invention provides the use of plant growth regulators in enhancing symbiotic nitrogen fixation in leguminous plants under low light conditions.

[0056] In some implementations, the low-light environment includes: densely planted areas, strip-shaped mixed planting areas, understory areas, greenhouse facilities, cloudy / rainy days, and light intensities ≤500 μmol / m². 2 / s environment.

[0057] Preferably, in the low-light environment, the light intensity is ≤500 μmol / m 2 / s, light intensity is 400umol / m 2 / s~500umol / m 2 / s, light intensity is 300umol / m 2 / s~400umol / m 2 / s, light intensity is 200umol / m 2 / s~300umol / m 2 / s, light intensity is 100umol / m 2 / s~200umol / m 2 / s, or light intensity ≤100umol / m 2 / s.

[0058] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0059] (1) The present invention provides plant growth regulators, including humic acid, fulvic acid and / or 5-aminolevulinic acid, which can improve the symbiotic nitrogen fixation of leguminous plants under low light conditions;

[0060] (2) The plant growth regulator of the present invention can significantly increase the chlorophyll content of leaves under low light, thereby promoting the capture of light energy by plants and increasing photosynthetic efficiency.

[0061] (3) By applying plant growth regulators to legumes, this invention enables legumes to maintain high tolerance under low light conditions such as dense planting, strip intercropping, under forest, greenhouse facilities, or cloudy and rainy days. It is simple to implement, saves manpower, and can be used for mechanized operations.

[0062] (4) This invention uses plant growth regulators humic acid, fulvic acid, and 5-aminolevulinic acid to treat legumes, thereby improving their symbiotic nitrogen fixation capacity under low light conditions and ensuring normal plant growth. Humic acid and fulvic acid, as carbon-containing natural plant growth regulators, can improve plant stress resistance, while 5-aminolevulinic acid, an amino acid and a precursor of tetrapyrrole compounds, is an important component in the synthesis of chlorophyll in green plants. Taking soybean as an example, this invention, based on research on the symbiotic nitrogen fixation and growth characteristics of soybean under low light conditions, found that plant growth regulators can significantly improve the symbiotic nitrogen fixation capacity and photosynthetic efficiency of soybean under low light conditions, increasing the number of nodules by 20%-90%, nitrogenase activity by 30%-260%, and plant biomass by 20%-80%, ensuring the effective operation of symbiotic nitrogen fixation in soybean under low light stress, thereby promoting normal plant growth and improving yield and quality.

[0063] Furthermore, research conducted by this invention demonstrates that the plant growth regulators humic acid, fulvic acid, and 5-aminolevulinic acid are used at low concentrations, resulting in low application costs and suitability for large-scale application. Currently, there are no reports on the application of plant growth regulators in legumes under low light conditions; therefore, this invention is of great significance for exploring efficient cultivation techniques for legumes under low light conditions.

[0064] Light is essential for symbiotic nitrogen fixation in legumes, but low light conditions are unavoidable due to various factors. When plants are under low light, their symbiotic efficiency is severely impaired. This invention unexpectedly discovered that plant growth regulators such as humic acid, fulvic acid, or 5-aminolevulinic acid at specific concentrations can compensate for the damage caused by low light to symbiotic nitrogen fixation in legumes, thereby improving the efficiency of symbiotic nitrogen fixation in legumes under low light and promoting plant growth. The method for improving symbiotic nitrogen fixation in legumes under low light provided by this invention can ensure normal plant growth. Attached Figure Description

[0065] Figure 1 The effect of low light on symbiotic nitrogen fixation in soybeans.

[0066] Figure 2 The effect of humic acid on symbiotic nitrogen fixation in soybeans under different light intensities.

[0067] Figure 3 The effects of low light on soybean growth.

[0068] Figure 4 The effects of humic acid on soybean growth under different light intensities.

[0069] Figure 5 The effect of fulvic acid on symbiotic nitrogen fixation in soybeans under different light intensities.

[0070] Figure 6The effect of fulvic acid on soybean growth under different light intensities.

[0071] Figure 7 The effect of ALA on symbiotic nitrogen fixation in soybean under different light intensities.

[0072] Figure 8 The effects of ALA on soybean growth under different light intensities. Detailed Implementation

[0073] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0074] The following embodiments and accompanying drawings are provided to aid in understanding the present invention. However, it should be understood that these embodiments and drawings are for illustrative purposes only and do not constitute any limitation. The actual scope of protection of the present invention is set forth in the claims. It should be understood that any modifications and changes can be made without departing from the spirit of the present invention.

[0075] The present invention will now be described in detail using soybean, a legume, as the test plant, but the present invention is not limited to these embodiments.

[0076] Example 1: Preparation of humic acid and fulvic acid

[0077] The humic acid used in this invention is obtained by purifying lignite after microbial fermentation, but includes, but is not limited to, chemical extraction and commercially available humic acid products. The humic acid is water-soluble and has a pH of 5-8. Fulvic acid refers to water-soluble humic acid products that have been further purified, and its elemental composition should contain 30%-70% carbon, 1%-5% nitrogen, and 25%-65% oxygen.

[0078] The crude fermented material from lignite bio-fermentation using Bacillus subtilis is mixed with an appropriate amount of water and stirred overnight. The stirred product is filtered through 8 layers of gauze, and the supernatant is air-dried to obtain crude humic acid. The crude humic acid is further dissolved in an appropriate amount of water, centrifuged to discard the precipitate, and the supernatant is dried at 60°C to obtain humic acid. Further, the humic acid obtained in the previous step is dissolved in water and passed through XAD-8 and cation exchange resin to obtain fulvic acid.

[0079] Example 2: Sources of ALA

[0080] The ALA used in this invention is derived from the biosynthesis of glucose and corn steep liquor by Staphylococcus pasteurization, including but not limited to ALA products obtained by fermentation by other microorganisms and extraction by commercially available chemical methods.

[0081] Example 3: Effects of humic acid on symbiotic nitrogen fixation in soybeans under low light conditions

[0082] This embodiment is set at 550umol / m 2 / s and 100umol / m 2 / s Two different light intensities, one of which is 550umol / m 2 / s represents the normal light intensity required for plant growth; as a control, 100 μmol / m 2 / s represents the low-light condition; all other conditions remain the same.

[0083] Soybean seeds germinated and growing uniformly on sterile water agar were transplanted into 10×10cm pots filled with pre-hydrated vermiculite:natural soil in a 3:1 ratio. One seed was planted in each pot, and each treatment was replicated 10 times. The growing conditions were 25℃, 50% humidity, 16 hours of light, and 8 hours of darkness.

[0084] The soybeans were treated for the first time 7 days after growth. In this example, 0.5 g / L humic acid was used, and 10 mL was applied to the roots of each plant. The treatment was repeated every 5 days. After 30 days of growth, the number of nodules was counted, the weight of the nodules was measured, and the nitrogenase activity of the nodules was measured.

[0085] The results are as follows Figure 1 As shown, weak light significantly inhibited symbiotic nitrogen fixation in soybeans, reducing the number of nodules and root nodule weight by 42.5% and 40.3%, respectively, and decreasing nitrogenase activity by 35.6%, severely impairing the nitrogen fixation efficiency of soybeans.

[0086] The results of applying humic acid under low light are as follows Figure 2 As shown, humic acid can not only enhance the symbiotic nitrogen fixation level of soybeans under normal light, significantly increasing the number and weight of root nodules by 25.3% and 37.6% respectively, and increasing nitrogenase activity by 46.0%, but also significantly compensate for the damage caused by weak light to nodulation, increasing the number and weight of root nodules under weak light by 53.2% and 70.6% respectively, restoring them to normal light levels. It also significantly increases nitrogenase activity under weak light, increasing it by 260.2%, even higher than the nitrogenase activity level under normal light, thus significantly enhancing the symbiotic nitrogen fixation capacity of soybeans under weak light.

[0087] Example 4: Effects of humic acid on soybean growth under low light conditions

[0088] The planting conditions for potted soybeans and the application method of humic acid are the same as in Example 3.

[0089] The growth phenotype of soybeans was observed and measured 30 days after growth.

[0090] The results are as follows Figure 3 As shown, weak light significantly reduced the photosynthetic intensity of soybeans, causing a 6.9% decrease in chlorophyll SPAD value. This resulted in excessive vegetative growth of the aboveground parts of the plant, longer internodes, thinner stems, and relatively sparse root systems, leading to a 28.6% decrease in root fresh weight and a 24.9% and 35.0% decrease in the dry matter of the aboveground and underground parts, respectively, severely damaging soybean growth.

[0091] The results of applying humic acid under low light are as follows Figure 4 As shown, humic acid not only promotes soybean growth under normal light intensity, increasing plant height by 15.3%, and aboveground fresh and dry weight by 12.2% and 19.7% respectively, and underground fresh and dry weight by 15.6% and 6.3% respectively; but also significantly improves the photosynthetic intensity of leaves under low light conditions, increasing chlorophyll SPAD by 14.8% and plant height by 54.5%, thereby increasing aboveground fresh and dry weight by 24.5% and 50.8% respectively, and underground fresh and dry weight by 16.2% and 23.4% respectively, thus compensating for the growth damage of soybeans caused by low light.

[0092] Example 5: Effect of fulvic acid on symbiotic nitrogen fixation in soybeans under low light conditions

[0093] The conditions for growing potted soybeans are the same as in Example 3.

[0094] The soybeans were treated for the first time 7 days after growth. In this example, 0.2 g / L fulvic acid was used, and 6 mL was sprayed on the leaves of each plant. The treatment was repeated every 5 days. After 30 days of growth, the number of nodules was counted, the weight of the nodules was measured, and the nitrogenase activity of the nodules was measured.

[0095] The results are as follows Figure 5 As shown, the application of fulvic acid can not only enhance the symbiotic nitrogen fixation level of soybeans under normal light, significantly increasing the number and weight of root nodules by 13.4% and 17.7% respectively, and increasing nitrogenase activity by 30.4%, but also significantly compensate for the damage caused by weak light to nodulation, increasing the number and weight of root nodules under weak light by 26.1% and 36.8% respectively, restoring them to normal light levels, and greatly increasing nitrogenase activity under weak light by 144.7%, even higher than the nitrogenase activity level under normal light, thus significantly enhancing the symbiotic nitrogen fixation capacity of soybeans under weak light.

[0096] Example 6: Effects of fulvic acid on soybean growth under low light conditions

[0097] The planting conditions for potted soybeans are the same as in Example 3, and the application method of humic acid is the same as in Example 5.

[0098] The growth phenotype of soybeans was observed and measured 30 days after growth.

[0099] The results are as follows Figure 6 As shown, fulvic acid not only increased the plant height of soybeans by 8.2% under normal light conditions, but also increased the fresh and dry weight of the aboveground parts by 2.9% and 1.8%, respectively. Under low light conditions, it also significantly improved the photosynthetic intensity of the leaves, resulting in a significant increase in chlorophyll SPAD by 11.6%, a plant height increase of 23.1%, an increase in fresh and dry weight of the aboveground parts by 17.9% and 27.7%, respectively, and an increase in fresh and dry weight of the underground parts by 1.5% and 10.3%, respectively, effectively alleviating the growth damage of soybeans caused by low light.

[0100] Example 7: Effects of ALA on symbiotic nitrogen fixation in soybeans under low light conditions

[0101] The conditions for growing potted soybeans are the same as in Example 3.

[0102] The soybeans were treated for the first time 7 days after growth. In this example, 0.045 g / L ALA was used, and 3 mL was sprayed on the leaves of each plant. The treatment was repeated every 5 days. After 30 days of growth, the number of nodules was counted, the weight of the root nodules was measured, and the nitrogenase activity of the root nodules was measured.

[0103] The results are as follows Figure 7 As shown, ALA not only significantly increased the number and weight of soybean root nodules by 19.9% ​​and 22.9% under normal light conditions, and increased nitrogenase activity by 57.2%, but also significantly compensated for the damage caused by weak light to nodulation, increasing the number and weight of root nodules by 93.4% and 124.5% under weak light, respectively, and increasing nitrogenase activity by 82.4%, thus significantly enhancing the symbiotic nitrogen fixation capacity of soybeans under weak light.

[0104] Example 8: Effects of ALA on soybean growth under low light conditions

[0105] The planting conditions for potted soybeans are the same as in Example 3, and the application method of ALA is the same as in Example 7.

[0106] The growth phenotype of soybeans was observed and measured 30 days after growth.

[0107] The results are as follows Figure 8 As shown, ALA can significantly promote the growth of soybean plants under normal light conditions, increasing plant height by 45.4%, and increasing aboveground fresh and dry weight by 39.1% and 37.3%, respectively, while increasing underground fresh and dry weight by 3.8% and 29.3%, respectively. Under low light conditions, it can also significantly improve the photosynthetic intensity of leaves, significantly increasing chlorophyll SPAD by 26.6%, increasing plant height by 30.7%, and increasing aboveground fresh and dry weight by 147.8% and 81.5%, respectively, while increasing underground fresh and dry weight by 19.0% and 47.0%, respectively, effectively alleviating the damage to soybean growth caused by low light.

[0108] In summary, the plant growth regulators provided in this invention, when used in the symbiotic nitrogen fixation and growth of soybeans under low light conditions, significantly increase the number of nodules and nitrogenase activity in soybeans under low light, thereby improving nitrogen fixation efficiency and ensuring the nitrogen nutrition required for plant growth. Simultaneously, they significantly increase chlorophyll content in leaves, resulting in darker green leaves, enhanced photosynthesis, and promoted the synthesis and accumulation of photosynthetic products, reducing the adverse effects of low light on light-loving plants. This significantly increases the dry matter content of soybeans and provides sufficient materials and energy for symbiotic nitrogen fixation in legumes. Furthermore, the plant growth regulators used in this embodiment can also promote more developed root systems in soybeans under low light, enhancing their absorption of nutrients and water. These methods effectively alleviate the problem of low nitrogen fixation efficiency in legumes under low light, promote the growth of legumes under low light, and provide significant technical guidance for current legume cultivation models.

[0109] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for improving symbiotic nitrogen fixation in legumes under low light conditions, characterized in that, Includes the following steps: After germinating leguminous seeds, sow them. When the seedlings have grown to the point where the first pair of true leaves have opened, spray them with a plant growth regulator. The plant growth regulator is 5-aminolevulinic acid, which is obtained by microbial fermentation purification. 5-Aminolevulinic acid is applied by foliar spraying. The concentration of 5-aminolevulinic acid sprayed is 0.03~0.10 g / L, and the dosage is 2~10 ml per plant; The low-light environments include: densely planted areas, strip-shaped mixed planting areas, understory areas, greenhouse facilities, cloudy / rainy days, and light intensities ≤ 500 umol / m². 2 / s environment.

2. The method according to claim 1, characterized in that, Spraying should be done every 4 to 7 days.

3. The method according to claim 1, characterized in that, Before cultivation, the legume seeds are surface disinfected by placing the seeds in a container, adding anhydrous ethanol, gently shaking for 25-35 seconds, and discarding the anhydrous ethanol; adding sodium hypochlorite solution, gently shaking for 4-6 minutes, and discarding the sodium hypochlorite solution; and rinsing with sterile water 6-8 times.

4. The method according to claim 1, characterized in that, The culture was carried out in the dark at 26-30℃ for 36-48 hours.

5. The method according to claim 4, characterized in that, The microorganism in question is Staphylococcus pasteurellum.

6. The use of plant growth regulators in enhancing symbiotic nitrogen fixation in leguminous plants under low light conditions; among which, The plant growth regulator is 5-aminolevulinic acid; the low-light environment includes: densely planted areas, strip intercropping areas, understory areas, greenhouse facilities, cloudy / rainy days, and light intensity ≤ 500 umol / m². 2 The environment is / s; the 5-aminolevulinic acid is obtained by microbial fermentation purification.

7. The use according to claim 6, characterized in that, The microorganism in question is Staphylococcus pasteurellum.

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