Efficient nitrogen-fixing bacteria and application thereof in promoting nitrogen absorption of plants

Abstract

The invention discloses a high-efficiency nitrogen-fixing bacterium. The high-efficiency nitrogen-fixing bacterium is sphingomonas paucimobilis of which the preservation number is CGMCC (China General Microbiological Culture Collection Center) No.32226. The invention also discloses a preparation method of the high-efficiency nitrogen-fixing bacterium. The invention further discloses a method for promoting plant nitrogen absorption. The invention further discloses application of the efficient nitrogen-fixing bacteria in promoting nitrogen absorption of plants. The invention also discloses a plant growth promoter. According to the invention, a sphingomonas paucimobilis strain with efficient nitrogen fixation capability is found through research, and the strain can effectively promote nitrogen absorption of plants and root growth of the plants and significantly improve the biomass of the plants. When the efficient nitrogen-fixing bacterium is applied to agricultural production, the nitrogen supply capacity of soil can be effectively improved, the growth environment of plants can be improved, and a new technical means is provided for agricultural sustainable development.

Description

Technical Field

[0001] The invention relates to the technical field of microorganisms, and in particular to a highly efficient nitrogen-fixing bacterium and an application thereof in promoting nitrogen absorption by plants. Background Art

[0002] Nitrogen is an essential element for plant growth and development. It participates in many physiological processes in plants and is a component of important molecules such as amino acids and proteins. The nitrogen source of plants mainly comes from nitrogen fertilizers and nitrogen-fixing microorganisms in the soil. The nitrogen source in the soil is often insufficient to meet the needs of plant growth, especially in poor soils and farmland environments. The use of nitrogen fertilizers has become an important means to increase yields in agricultural production. However, excessive use of nitrogen fertilizers can lead to environmental pollution, such as eutrophication of water bodies, soil acidification, and greenhouse gas emissions. Therefore, how to improve the utilization efficiency of nitrogen and reduce negative impacts on the environment has become an important research task in the current agricultural field.

[0003] Azotobacteria are bacteria that can convert nitrogen in the air into amino nitrogen (NH 4 + ) microorganisms, which play an important role in the nitrogen cycle in nature. By applying nitrogen-fixing bacteria, the content of available nitrogen in the soil can be effectively increased, reducing the dependence on exogenous nitrogen fertilizers, thereby promoting the growth and development of plants. In addition, nitrogen-fixing bacteria can also improve the physical and chemical properties of the soil, enhance soil fertility, restore the ecological balance of the soil, and have important functions such as reducing soil salinization and improving crop resistance.

[0004] At present, many studies have shown that nitrogen-fixing bacteria play a significant role in promoting plant growth and increasing crop yields. In particular, salt-tolerant nitrogen-fixing bacteria are used in the cultivation of crops in saline-alkali land, which can significantly improve the biomass and yield of plants. Chaudhary et al.'s research shows that inoculating salt-tolerant nitrogen-fixing bacteria into wheat can significantly increase the biomass and grain yield of wheat in saline-alkali land; Wang Huiqiao et al.'s research found that by using nitrogen-fixing bacteria to increase the effective nitrogen content of saline-alkali soil, corn growth was promoted, thereby increasing corn yield. In addition, nitrogen-fixing bacteria also have a significant promoting effect on forest plants. Qin Xiaohong et al. significantly improved the plant height and ground diameter of eucalyptus seedlings through the inoculation of nitrogen-fixing bacteria.

[0005] However, most current research and applications focus on specific types of nitrogen-fixing bacteria, and the effectiveness of many nitrogen-fixing bacteria under different environmental conditions has not been fully explored. In particular, those nitrogen-fixing bacteria that have the ability to dissolve phosphorus and improve nitrogen absorption efficiency under low nitrogen conditions have not been widely used. Therefore, developing new efficient nitrogen-fixing strains and studying their potential in improving soil fertility and increasing crop growth have important theoretical and practical significance. Summary of the invention

[0006] To overcome the above defects, the present invention provides a highly efficient nitrogen-fixing bacterium and its application in promoting nitrogen absorption by plants.

[0007] On the one hand, the present invention provides a highly efficient nitrogen-fixing bacterium, which is Sphingomonas paucimobilis with a deposit number of CGMCC No.32226.

[0008] According to the present invention, there is no particular requirement for the total viable count of the efficient nitrogen-fixing bacteria. Preferably, the total viable count of the efficient nitrogen-fixing bacteria is 10 8 -10 9 CFU / mL (based on the dry basis of the composite bacterial agent).

[0009] In a second aspect, the present invention also provides a method for promoting plant nitrogen absorption, comprising the following steps:

[0010] (1) preparing the above-mentioned Sphingomonas paucimobilis into a bacterial agent;

[0011] (2) Applying the microbial agent to plants by spraying, root irrigation or seed coating;

[0012] (3) Promote nitrogen absorption and growth of plants through the nitrogen fixation and hormone secretion functions of the fungus.

[0013] According to the present invention, the method is suitable for improving nitrogen absorption of Arabidopsis thaliana or Chinese fir, and significantly increases the biomass of the above-ground part and the underground part of Arabidopsis thaliana or Chinese fir.

[0014] In a third aspect, the present invention also provides the use of efficient nitrogen-fixing bacteria in promoting plant nitrogen absorption. The efficient nitrogen-fixing bacteria is Sphingomonas paucimobilis with a preservation number of CGMCC No. 32226, which can increase the biomass of plants by promoting plant root growth and improving root nitrogen absorption activity.

[0015] According to the present invention, the above application can significantly improve the growth and biomass of plants under low nitrogen conditions.

[0016] In a fourth aspect, the present invention further provides a plant growth promoter, which comprises Sphingomonas paucimobilis.

[0017] According to the present invention, the plant growth promoter can be used to improve the growth performance of crops in poor soil.

[0018] The present invention has discovered a strain of Sphingomonas oligotrophicus with high-efficiency nitrogen fixation ability through research. The strain can effectively promote the absorption of nitrogen by plants and promote the growth of plant roots, and significantly increase plant biomass. By applying the high-efficiency nitrogen-fixing bacteria of the present invention to agricultural production, the nitrogen supply capacity of the soil can be effectively improved and the plant growth environment can be improved, providing new technical means for sustainable agricultural development.

[0019] Biological Deposit

[0020] The Sphingomonas paucimobilis of the present invention was deposited in the General Microbiology Center of China National Microbiological Culture Collection Administration (abbreviated as CGMCC, address: No. 3, Yard No. 1, Beichen West Road, Chaoyang District, Beijing, Postal Code: 100101) on October 16, 2024, with a deposit number of CGMCC No. 32226. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0022] Figure 1 It is the phosphate-dissolving circle of the efficient nitrogen-fixing bacteria of the present invention.

[0023] Figure 2 This is a diagram of the growth status of Arabidopsis thaliana under the treatment of the high-efficiency nitrogen-fixing bacteria of the present invention (A: normal 1 / 2MS + nitrogen-fixing bacteria treatment; B: normal 1 / 2MS + sterile water treatment; C: low nitrogen 1 / 2MS + nitrogen-fixing bacteria treatment; D: low nitrogen 1 / 2MS + sterile water treatment).

[0024] Figure 3 The figures are the increase bar graphs of plant height and ground diameter of Chinese fir under the treatment of the high-efficiency nitrogen-fixing bacteria of the present invention (A: plant height increase bar graph; B: ground diameter increase bar graph). DETAILED DESCRIPTION

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The efficient nitrogen-fixing bacteria used in the following examples are Sphingomonas paucimobilis with a preservation number of CGMCC No. 32226. The total viable bacteria count in the efficient nitrogen-fixing bacteria is 10 8 -10 9 CFU / mL (based on the dry basis of the composite bacterial agent).

[0029] 1 Materials and methods

[0030] 1.1 Isolation and identification of bacterial strains

[0031] In the mixed forest of different ages of Chinese fir and nanmu in Shouchang Forest Farm, Jiande City, Zhejiang Province, rhizosphere soil of nanmu was collected, stored in ice packs, and transported back to the laboratory. 10g of soil sample was added to 90mL of liquid culture medium, the composition of the culture medium was: KH 2 PO 4 0.2 g, MgSO 4 7H 2 O 0.2g, NaCl 0.2g, CaCO 3 5.0g, mannitol 10g, CaSO 4 ·2H 2 O 0.1g, distilled water 1000mL, pH value adjusted to 6.5-7.0, 28℃ shaking culture for 4-5d (180r / min). Use gradient dilution method to prepare 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 Take 0.1 mL of the diluted soil suspension and apply it to the nitrogen-fixing bacteria culture medium (KH 2 PO 4 0.2 g, MgSO 4 7H 2 O 0.2g, NaCl 0.2g, CaCO 3 5.0g, mannitol 10g, CaSO 4 ·2H 2O 0.1g, agar 18g, distilled water 1000mL, pH 6.5-7.0), cultured at 28℃ for 4d, and each concentration was repeated 3 times. During the culture period, the growth of the colonies on the plate and the changes in the transparent circle around the colonies were observed, and the single colonies with obvious transparent circles formed on the culture medium were picked and further purified by streaking. PCR identification was performed on the single colonies, and 16S rRNA sequencing was performed on the single colonies with specific bands (sequencing was 16S universal primers 27F and 1492R). The sequence was compared with the available 16S rRNA gene sequence in the gene library by BLAST, and the strain was inoculated on the LB slant culture medium and stored in a refrigerator at 4℃ for standby use, which was the efficient nitrogen-fixing bacteria of the present invention.

[0032] 1.2 Evaluation of growth-promoting properties of bacterial strains

[0033] (1) Determination of nitrogen fixation efficiency

[0034] The obtained nitrogen-fixing bacteria were inoculated into LB liquid medium (tryptone 10 g, yeast extract 10 g, sodium chloride 10 g, distilled water 1000 mL, pH 7.0-7.2), cultured at 28 ° C, 180 r / min for 2 days, and the bacterial solution concentration was adjusted to OD 600 = 0.5, inoculated into DO culture medium (sucrose 15g, malic acid 5g, K 2 HPO 4 ·H 2 O 0.1g, KH 2 PO 4 ·H 2 O 0.4 g, NaCl 0.1 g, NaMoO 4 ·H 2 O 0.002g, FeCl 3 0.001 g, CaCl 2 ·H 2 O 0.002 g, MgSO 4 7H 2 O0.2g, distilled water 1000mL, pH 7.0), shake well, and culture in a shaking incubator at 28℃, 120r / min for 5 days, then take out to determine sugar and nitrogen. Sugar determination was done by anthrone photoelectric colorimetry, and nitrogen was measured by semi-micro colorimetry.

[0035] i. Anthrone photoelectric colorimetry

[0036] Draw a standard glucose solution (1g / L) and dilute it to different concentration gradients (0mg / L, 10mg / L, 20mg / L, 40mg / L, 60mg / L, 80mg / L, 100mg / L, 200mg / L), and draw a standard curve. Take 2mL of fermentation broth and dilute it to 100mL, take 1mL of this dilution in a colorimetric tube, add 1mL of distilled water and 4mL of 0.2% (m / v) anthrone solution (0.2g anthrone dissolved in 100mL concentrated sulfuric acid), shake well, ice bath for 10min, heat in a water bath at 80℃ for 15min to fully develop color, cool for 30min, and measure the absorbance at a wavelength of 620nm with an ultraviolet spectrophotometer. Set the treatment without nitrogen-fixing bacteria as the blank control, and set 3 parallels for each group.

[0037] Sugar consumption (w 1 ), g / 100mL:

[0038] w 1 =(m 1 -m 2 )×100 / m×100×10 -6

[0039] m 1 ——Sugar content of blank control found on the standard curve, mg / L;

[0040] m 2 ——Sugar content of the test group found on the standard curve, mg / L;

[0041] m——the volume of fermentation liquid absorbed, mL.

[0042] ii. Total nitrogen colorimetric determination

[0043] Weigh 0.4716 g of ammonium sulfate that has been dried at 105°C for 1 hour to constant weight, dissolve it in water and dilute it to 100 mL to make a 1 mg / mL nitrogen-containing standard solution. Take this solution and dilute it to different concentration gradients (0 μg / mL, 0.5 μg / mL, 1 μg / mL, 2.5 μg / mL, 5 μg / mL, 10 μg / mL) to draw a standard curve. Pipette 1 mL of fermentation broth into a digestion tube, add 3 mL of concentrated sulfuric acid, 0.1 g of catalyst (10 g K 2 SO 4 With 1gCuSO 4Grind together) and 5 drops of 30% hydrogen peroxide in a digester to digest until clear, remove and cool. Add a little distilled water and shake well, add 40% (m / v) sodium hydroxide solution until copper hydroxide blue precipitate appears (about 10mL), add 1mL50% (m / v) potassium sodium tartrate solution to remove the hydroxide precipitate that masks calcium and magnesium, transfer all the liquid in the digestion tube to a 50mL volumetric flask, dilute to the scale, shake well, and filter. Take 10mL of the filtrate in a colorimetric tube, add 1mL of 2mol / L sodium hydroxide solution, 1mL of 50% (m / v) potassium sodium tartrate solution, and 3mL of Nessler's reagent in sequence, shake well, color for 2min, immediately pour into a colorimetric cup, and measure the absorbance at 600nm with a UV spectrophotometer.

[0044] Nitrogen content (w 2 ), g / 100mL

[0045] w 2 =(m 1 -m 2 )×50 / m×100×10 -6

[0046] m 1 ——Nitrogen content of the test group found on the standard curve, μg / mL;

[0047] m 2 ——Nitrogen content of blank control obtained from the standard curve, μg / mL;

[0048] m——the volume of fermentation liquid absorbed, mL.

[0049] Nitrogen fixation efficiency value (p), mg / g

[0050] p=(w 2 ×10 3 ) / w 1

[0051] w 1 ——Sugar consumption, g / 100mL;

[0052] w 2 ——Nitrogen content, g / 100mL.

[0053] (2) Evaluation of phosphate solubilization function

[0054] i. Qualitative evaluation of phosphate solubilization ability

[0055] The nitrogen-fixing bacteria were inoculated into phosphate-solubilizing medium plates (10.0 g glucose, 0.5 g ammonium sulfate, 0.3 g sodium chloride, 0.3 g magnesium sulfate, 0.03 g manganese sulfate, 0.3 g potassium sulfate, 0.03 g ferrous sulfate, 5.0 g calcium phosphate, 15.0 g agar, 1000 mL distilled water, pH 7.0-7.5) by the four-point method, and cultured in a 30°C constant temperature incubator for 4-7 days. The ratio (D / d) of the phosphate-solubilizing circle diameter (D) of the strain to the colony diameter (d) was observed and compared, and the phosphate-solubilizing ability of each strain was preliminarily judged according to the D / d value. In 5 mL PVK liquid culture medium (10.0 g glucose, 0.5 g ammonium sulfate, 0.3 g sodium chloride, 0.3 g magnesium sulfate, 0.03 g manganese sulfate, 0.3 g potassium sulfate, 0.03 g ferrous sulfate, 5.0 g calcium phosphate, 1000 mL distilled water, pH 7.0-7.5), 1 μL of the isolated phosphate-solubilizing bacteria was added, and the phosphate-solubilizing content of the bacterial agent was quantitatively analyzed by the molybdenum antimony colorimetric method after incubation at 28°C in a shaking incubator for 5 days.

[0056] ii. Quantitative evaluation of phosphate solubilization capacity

[0057] Will KH 2 PO 4 Continue drying at 50°C, dissolve 0.44g potassium dihydrogen phosphate in 100mL distilled water, add 5mL concentrated sulfuric acid solution, and dilute to 1000mL with distilled water. Take 10mL of the solution in a 200mL volumetric flask, add water to the mark, and make a solution with a concentration of 5mg·L -1 Take the standard solution and dilute it to different concentration gradients (0 mg / L, 0.2 mg / L, 0.4 mg / L, 0.6 mg / L, 0.8 mg / L, 1 mg / L) to draw a standard curve.

[0058] Dilute to a concentration of OD 600 = 0.5 bacterial solution was inoculated into PVK medium at 5% inoculation volume, and cultured at 28°C and 140rpm for 5 days. After 5 days, the bacterial solution was shaken and 15mL was injected into a sterile centrifuge tube, and after centrifugation at 4000rpm for 5 minutes, the supernatant was taken for testing.

[0059] The effective phosphorus content of the bacterial liquid was determined by the molybdenum antimony colorimetric method. Measure 153 mL of concentrated sulfuric acid and put it into a beaker with 400 mL of distilled water, stirring continuously until completely cooled. Grind the ammonium molybdate into fine powder, prepare 300 mL of distilled water at about 60°C, dissolve 10 g of ammonium molybdate in the distilled water and cool to room temperature. Mix the sulfuric acid solution and the ammonium molybdate solution evenly. Add 100 mL of 5 mg·L-1 potassium antimony tartrate solution, add distilled water to dilute to 1000 mL after cooling, shake well, and prepare a molybdenum antimony storage solution. Weigh 1.5 g of ascorbic acid and dissolve it in 100 mL of molybdenum antimony storage solution to prepare a molybdenum antimony colorimetric agent. Weigh 0.2 g of 2,4-dinitrophenol and dissolve it in 100 mL of distilled water to prepare a 2,4-dinitrophenol indicator.

[0060] Take 1mL of the supernatant to be tested and add it to a colorimetric tube, dilute it to 20mL with distilled water. Add 2 drops of 2,4-dinitrophenol indicator and 5mL of molybdenum antimony anticolorimetric agent, shake well, dilute to 50mL, and let it stand. Use the blank solution as the reference solution to adjust the zero, perform colorimetry at a wavelength of 700nm, and obtain the effective phosphorus content of the strain according to the phosphorus standard curve.

[0061] (3) Evaluation of IAA production capacity

[0062] Weigh 10 mg of IAA and dissolve it in 10 mL of 50% methanol to prepare an IAA standard solution. Dilute the solution with 50% methanol to different concentrations (0 μg / mL, 10 μg / mL, 20 μg / mL, 30 μg / mL, 40 μg / mL, 50 μg / mL, 100 μg / mL) and dilute to a concentration of OD 600 = 0.5 was inoculated into King's liquid medium (peptone 20.0 g, K 2 HPO 4 1.725 g, glycerol 15.0 mL, MgSO 4 7H 2 O 1.5g, tryptophan 0.1g, pH 7.2), repeated 3 times. After culturing at 37℃ shaker for 12 days, centrifuge at 4000rpm for 10min, aspirate the supernatant, add Salkowski colorimetric solution (0.5mol / L ferric chloride 1mL added to 30ml concentrated sulfuric acid, dilute to 50mL) in a 1:1 ratio, react for 30min in the dark, and measure its absorbance at 530nm wavelength with UV spectrophotometer. Calculate the IAA concentration in the sample using the standard curve.

[0063] 1.3 Preparation of nitrogen-fixing bacteria

[0064] Pick one loop of the purified Sphingomonas paucimobilis strain and inoculate it into LB liquid medium (tryptone 10g, yeast extract 10g, sodium chloride 10g, distilled water 1000mL, pH 7.0-7.2), and culture it at 28℃, 180r / min for 2d. Check the growth of the bacteria regularly during the culture process to ensure that the bacteria are fully reproduced and maintain high activity. After the culture is completed, centrifuge at 4000rpm for 10min, remove the upper culture solution, and obtain a bacterial precipitate containing high-concentration bacteria. Resuspend the precipitate in an appropriate amount of physiological saline and adjust the concentration to 1×108CFU / mL. A solid bacterial agent is obtained by freeze drying. The obtained solid bacterial agent is placed in a sealed packaging bag to ensure sterile packaging. Store the bacterial agent in a cool and dry place and keep it in a low temperature environment below 4℃ to extend the shelf life.

[0065] 1.4 Effects of co-cultivation on the growth of Arabidopsis thaliana

[0066] Arabidopsis thaliana was selected as the experimental plant and cultured in conventional 1 / 2MS and low nitrogen 1 / 2MS medium. Four groups were set up in the experiment: A: normal 1 / 2MS + nitrogen-fixing bacteria treatment; B: normal 1 / 2MS + sterile water treatment; C: low nitrogen 1 / 2MS + nitrogen-fixing bacteria treatment; D: low nitrogen 1 / 2MS + sterile water treatment. Arabidopsis thaliana seeds were sterilized with ddH 2 Wash once with 75% alcohol and shake for 90 seconds, sterilize with ddHO 2 Wash with 2% NaClO for 3 times, add 2% NaClO and shake for 10 min, then add sterile ddHO 2 O wash 3 times. Add 1mL sterile water, use a pipette to absorb the seeds and lay them on a 1 / 2MS culture dish, shake evenly, and pour out excess water. Seal the culture dish with a sealing film, place it in a 4℃ refrigerator for 2 days, take it out and place it in a constant temperature incubator for 4 days, then select 5 Arabidopsis seedlings with the same growth and transfer them to low nitrogen 1 / 2MS and normal 1 / 2MS culture media, arrange the transferred seedlings on the same horizontal line, absorb and activate them, and dilute them with sterile water to OD 600 10 μL of the strain with a concentration of 0.1 was drawn 3 cm below the sterile seedlings, and the plate was placed vertically on the plate rack. All treatment groups were cultured at 28°C, with a photoperiod of 12 hours / day and a 10-day experimental period. The effect of the inoculant on the growth of Arabidopsis was evaluated by measuring indicators such as root biomass and aboveground biomass.

[0067] 1.5 Effects of inoculation on the growth of Chinese fir seedlings

[0068] The flower pots used were 25 cm in diameter and 28 cm in height. Each pot was filled with 4 kg of soil (the ratio of yellow soil to perlite was 3:1). After the half-year-old asexual Chinese fir seedlings were transplanted into the pots and allowed to grow for 60 days, Chinese fir seedlings with similar growth were selected for fungus treatment. The high-temperature inactivated bacterial solution was used as the control group. Each group of treatments was set up with 8 parallels. The nitrogen-fixing bacteria were inoculated into LB liquid medium and cultured at 28°C, 180 r / min for 3 days, and then diluted with sterile water to 5.5×10 6 100 mL of bacterial solution was applied to each pot, once every 7 days, for a total of 4 times, and the height and ground diameter of the Chinese fir seedlings were measured on the day of the first bacterial treatment and 30 days later. The growth rates of the height and ground diameter of the Chinese fir seedlings were compared to evaluate the growth-promoting effect of nitrogen-fixing bacteria on Chinese fir seedlings.

[0069] 1.6 Data Analysis

[0070] IBM SPSS Statistics (version 22.0) was used for data analysis, GraphPad Prism 7.00 software was used for graphics, one-way analysis of variance was used, and Duncan's new multiple range method was used for multiple comparisons.

[0071] 2 Results and Analysis

[0072] 2.1 Isolation and screening of nitrogen-fixing strains

[0073] A nitrogen-fixing bacteria species was isolated from the rhizosphere soil of the mixed forest of Chinese fir and nanmu, numbered N23, and sent to Beijing Qingke Xinye Biotechnology Co., Ltd. for sequencing and confirmed to be the nitrogen-fixing bacteria Sphingomonas paucimobilis. After the nitrogen-fixing bacteria was inoculated with DO culture solution for 5 days, the nitrogen-fixing efficiency of N23 was measured by the fixed sugar nitrogen method to be 3.23±0.39 mg / g.

[0074] 2.2 Evaluation of growth-promoting properties of nitrogen-fixing strains

[0075] After the nitrogen-fixing bacteria N23 was inoculated into King's liquid medium and cultured for 12 days, the IAA secretion was measured by colorimetry to be 19.19±2.19μg / mL. After the nitrogen-fixing bacteria was inoculated into PVK liquid medium and cultured for 5 days, the effective phosphorus increment was measured by molybdenum antimony colorimetry to be 90.71±4.38mg / mL; the phosphorus dissolution circle (D / d) value of the strain was 3.01±0.34 (see Figure 1 ).

[0076] 2.3 Effects of nitrogen-fixing bacteria treatment on root growth of Arabidopsis thaliana

[0077] The nitrogen-fixing bacteria were co-cultured with Arabidopsis for 10 days and the root growth was observed. Figure 2As shown, the root system of Arabidopsis thaliana treated with nitrogen-fixing bacteria N23 was more developed than that of the control group treated with sterile water, and the lateral roots were significantly increased.

[0078] 2.4 Effects of nitrogen-fixing bacteria treatment on Arabidopsis biomass

[0079] After the nitrogen-fixing bacteria and Arabidopsis were co-cultured for 10 days, the fresh weight of Arabidopsis was weighed on a balance. The results showed (Table 1) that the biomass of the whole plant of Arabidopsis with N23 addition was higher than that of the control group, whether under normal nitrogen levels or low nitrogen conditions. Specifically, under normal nitrogen levels, the biomass of the whole plant of Arabidopsis treated with N23 was 25.9 g, while that of the control group was only 10.7 g; under low nitrogen conditions, the biomass of the whole plant of Arabidopsis treated with N23 was 26.2 g, while that of the control group was 6.9 g. In addition, the N23 treatment also significantly increased the biomass of the aboveground and underground parts. These results show that the nitrogen-fixing bacteria N23 can effectively promote the growth of Arabidopsis under different nitrogen levels, especially under low nitrogen conditions.

[0080] Table 1 Biomass of Arabidopsis thaliana treated with nitrogen-fixing bacteria

[0081]

[0082] 2.5 Effects of nitrogen-fixing bacteria treatment on the growth of Chinese fir seedlings

[0083] After 30 days of inoculation of nitrogen-fixing bacteria into Chinese fir seedlings, the average plant height increase of Chinese fir seedlings in the nitrogen-fixing bacteria treatment and the control group was 16.2±2.5% and 11.3±1.3%, respectively, and the average ground diameter increase was 9.4+2.2% and 5±1.1%, respectively. The results showed that nitrogen-fixing bacteria N23 can effectively promote the growth of Chinese fir seedlings.

[0084] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A highly efficient nitrogen-fixing bacterium, characterized in that: The high-efficiency nitrogen-fixing bacteria is Sphingomonas paucimobilis with a preservation number of CGMCC No.32226.

2. The efficient nitrogen-fixing bacteria according to claim 1, characterized in that The total number of viable bacteria in the highly efficient nitrogen-fixing bacteria is 10 8 -10 9 CFU / mL.

3. A method for promoting nitrogen absorption in plants, characterized in that: The following steps are included: (1) preparing the Sphingomonas paucimobilis described in claim 1 into a bacterial agent; (2) applying the bacterial agent to plants by spraying, root irrigation or seed coating; (3) The nitrogen fixation and hormone secretion functions of the bacterial agent promote the nitrogen absorption and growth of the plant.

4. The method according to claim 3, characterized in that: The method is suitable for improving nitrogen absorption of Arabidopsis thaliana or Chinese fir, and significantly increases the biomass of the above-ground part and the underground part of the Arabidopsis thaliana or Chinese fir.

5. The use of efficient nitrogen-fixing bacteria in promoting nitrogen absorption by plants, characterized in that: The high-efficiency nitrogen-fixing bacteria is Sphingomonas paucimobilis with a preservation number of CGMCC No. 32226, and can increase the biomass of the plant by promoting the growth of the plant root system and improving the nitrogen absorption activity of the root system.

6. The use according to claim 5, characterized in that: The application can significantly improve the growth and biomass of the plant under low nitrogen conditions.

7. A plant growth promoter, characterized in that The plant growth promoter comprises the Sphingomonas paucimobilis according to claim 1.

8. The plant growth promoter according to claim 7, characterized in that The plant growth promoter can be used to improve the growth performance of crops in poor soil.

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