Composite microbial inoculant for coupling straw decomposition and soil carbon sequestration and preparation method thereof

Abstract

The invention discloses a complex microbial inoculant for coupling straw decomposition and soil carbon sequestration and a preparation method thereof, the complex microbial inoculant can rapidly promote degradation of lignocellulose of straw in soil by compounding bacillus subtilis, bacillus licheniformis, pseudomonas aeruginosa and the like, provides a basic material energy source for activity of soil microorganisms, and has the advantages of simple preparation process and low cost. Meanwhile, corresponding microorganisms achieve long-term storage of organic carbon through humus stabilization and mineral substance combined carbon (MAOC) stabilization, the storage efficiency of the organic carbon is remarkably improved through nano Fe3O4, and under the synergistic effect of all strains in the complex microbial inoculant, the carbon loss of straw returning can be effectively reduced, the carbon immobilization capacity of soil is improved, and the soil quality is improved. The organic carbon content in the soil is increased.

Description

Technical Field

[0001] The present invention relates to the field of microbial technology, and particularly relates to a composite microbial agent for coupling straw decomposition and soil carbon sequestration and a preparation method thereof. Background Art

[0002] In recent years, the problem of global climate change has attracted wide attention. The emission of greenhouse gases, especially carbon dioxide, is considered to be the main driving factor for global warming. In order to slow down climate change and control the concentration of carbon dioxide, carbon sequestration and absorption have become an important environmental protection technology.

[0003] In nature, soil is an important carbon pool. The organic carbon storage in soil is much higher than that in the atmosphere and plants. Therefore, improving soil carbon storage and promoting soil carbon sequestration by optimizing soil management have become one of the important ways to slow down global climate change.

[0004] The organic carbon in soil comes from the decomposition process of plant residues, animal remains and other organic substances. Straw is one of the main plant residues produced in the agricultural production process, accounting for more than 70% of agricultural waste. Microorganisms play a key role in the straw decomposition process and can convert complex organic substances in straw into organic carbon that can be absorbed and utilized by soil. At present, there are already some microbial agents specifically used for straw decomposition on the market, but most products can only promote straw degradation singly and fail to effectively improve the soil carbon sequestration ability, which needs to be improved. Summary of the Invention

[0005] To solve the above at least one technical defect, the present invention provides the following technical solutions: This application document discloses a composite microbial agent for coupling straw decomposition and soil carbon sequestration, including: Functional bacterium A, which includes: Bacillus subtilis with the preservation number CGMCC.NO.26196 and Bacillus licheniformis with the preservation number CGMCC.NO.26194, and the liquid volume ratio of the two is 1 - 2:2 - 6; Functional bacterium B, which is Pseudomonas aeruginosa with the preservation number CGMCC.NO.26195; Functional bacterium C, which is Trichoderma longibrachiatum with the preservation number CGMCC.NO.40444; Protectant and nano - Fe 3 O 4 。

[0006] Among them, the liquid volume ratio of the functional bacterium A, the functional bacterium B, and the functional bacterium C is 1 - 2:4 - 8:2 - 7; nano - Fe 3 O 4It accounts for 0.1wt%-0.5wt% in the compound microbial agent, and the protective agent accounts for 2wt%-5wt% in the compound microbial agent.

[0007] As Figure 1 shown, the working principle of the microbial agent is as follows: I. Degradation of lignocellulose Bacillus subtilis CGMCC NO.26196 and Bacillus licheniformis CGMCC NO.26194 drive the efficient degradation of lignocellulose through multi-enzyme synergy. Bacillus subtilis CGMCC NO.26196 secretes endoglucanase and manganese peroxidase, randomly cleaves the β-1,4-glycosidic bond from the inside of the cellulose chain and oxidizes the benzene ring structure of lignin. At the same time, its β-glucosidase relieves the product inhibition of cellobiose. Bacillus licheniformis CGMCC NO.26194, under the action of exoglucanase and xylanase, continuously releases monosaccharides from the end of the cellulose chain and efficiently depolymerizes hemicellulose. Its laccase indirectly promotes lignin depolymerization by assisting in the oxidation of phenolic monomers. The two strains significantly improve the lignocellulose degradation efficiency through metabolic complementarity. At the same time, through partial lignin depolymerization and the secretion of surface-active substances, the substrate accessibility is enhanced, and the release of degradation products is promoted. Cellulose is decomposed into glucose, providing an energy source and carbon skeleton for microorganisms. Hemicellulose is decomposed into arabinose, mannose, etc.; lignin is degraded into polyphenols and other substances. II. Stabilization of mineral-associated organic carbon (MAOC) in soil Soil organic carbon (SOC) is the basis index for the effect of straw entering the soil to achieve carbon fixation. The stability and dynamic characteristics of soil organic carbon (SOC) are jointly determined by its solid-phase carbon pool (MAOC and POC) and mobile components. Microorganisms decompose straw and transform substances such as lignin to form humus. Thus, part of the humus combines with minerals to form stable MAOC, which serves as the core stable component of SOC; while the other part of the free humus belongs to active POC or participates in the carbon cycle as an intermediate product of dynamic transformation. In addition, from a biochemical perspective, dissolved organic carbon (DOC) and soil microbial biomass carbon (MBC) both belong to independent mobile carbon pools, with migration and transformation characteristics different from those of the solid-phase carbon pool, mainly characterizing the biochemical activity during the carbon transformation process. In the pathway of mineral-associated organic carbon (MAOC) stabilization, the decomposition products of hemicellulose, mannose and mannuronic acid, are transformed into extracellular polysaccharides (EPS) by microorganisms such as Pseudomonas aeruginosa CGMCC.NO.26195. Among them, alginate, as the main component of EPS, the carboxyl group (-COOH) on its mannuronic acid chain binds to the surface of clay minerals through cations such as Ca 2+ 、Fe 3+ or Al 3+ and other cations to form an "EPS-cation-mineral" ternary complex. Nano-Fe 3 O 4Function 1: Its high specific surface area (>200 m 2 / g) and positive surface charge (Zeta potential +25 mV at pH 5 - 7) significantly enhance the adsorption efficiency of alginate with montmorillonite or hematite; Function 2: The colloidal coating layer formed by nano-Fe 3 O 4 and EPS can effectively block the contact between hydrolase and organic substrates, increase the residual rate of cellulase hydrolysis, and significantly delay the mineralization release of carbon.

[0008] III. Soil humus stabilizationIn the humus stabilization pathway, the degradation of lignin is the key step to initiate carbon transformation. Trichoderma longibrachiatum CGMCC.NO.40444 can secrete lignin peroxidase and manganese peroxidase on the one hand. In the presence of Mn 2+ cofactor and H 2 O 2 , the β-O-4 ether bond of lignin is cleaved through a free radical chain reaction to release phenolic monomers such as vanillic acid and coniferyl alcohol. These polyphenolic substances then become the precursors for humus synthesis. On the other hand, it also secretes laccase to catalyze the oxidative dehydrogenation reaction of phenolic monomers to generate quinone free radicals, and further forms polyaromatic compounds, namely humic acid precursors, through C-O or C-C bond coupling. In this enzymatic process, one of the functions of nano-Fe 3 O 4 is: through the redox activity of surface Fe 3+ , it accelerates the generation and stabilization of free radicals, increasing the polymerization reaction rate; Fe 3+ forms Fe-O-C coordination bonds with carboxyl and phenolic hydroxyl groups in humic acid molecules, significantly enhancing the chemical stability of humus; Function 2: Under alkaline or neutral conditions, nano-Fe 3 O 4 can also catalyze the non-enzymatic condensation process (Maillard reaction) of polyphenols and amino sugars to generate melanoidins, the humus precursor. Its conjugated carbonyl structure further enhances the ability to resist microbial decomposition.

[0009] The dual-pathway stabilization of straw residue carbon is a multi-process coupling system driven by microorganisms and mediated by minerals. Nano-Fe 3 O 4 realizes the efficient directional regulation of carbon flow through multiple mechanisms such as chemical catalysis, electron transfer, and physical protection to meet the carbon sequestration requirements under different soil types and climate conditions.

[0010] The protectant can improve the resistance of microorganisms, reduce the external influence on them, improve the stability of microbial cells, and then play a better role in the follow-up.

[0011] Further, the concentrations of Bacillus subtilis with the preservation number of CGMCC.NO.26196 and Bacillus licheniformis with the preservation number of CGMCC.NO.26194 in the functional bacterium A are 4-6×10 10 CFU / ml and 5-8×10 10 CFU / ml respectively, and the concentrations of the functional bacterium B and the functional bacterium C are 5-7×10 9 CFU / ml and 2-6×10 10 CFU / ml respectively.

[0012] Further, the protective agent includes 10-20wt% glycerol, 10-15wt% sucrose, 1-2wt% sodium alginate, 1-3wt% sodium chloride, and the balance is deionized water. Glycerol can be used as a protective agent to help maintain the structure of microbial cells, prevent dehydration and damage. Especially during cryopreservation, glycerol can effectively improve the survival rate of microorganisms. Sucrose can prevent the osmotic pressure imbalance of microbial cells, maintain the moisture inside the cells, and enhance the frost resistance of microorganisms. Sodium alginate, as a natural polymer, can form a film to protect microorganisms from the external environment, especially helping to preserve the integrity of cells. Sodium chloride is used to adjust the osmotic pressure and help maintain the stability of microbial cells.

[0013] This application document also discloses a preparation method of the above compound bactericide, which includes the following steps: S1. Mix the Bacillus subtilis bacterial liquid with the preservation number of CGMCC.NO.26196 with a concentration of 4-6×10 10 CFU / ml and the Bacillus licheniformis bacterial liquid with the preservation number of CGMCC.NO.26194 with a concentration of 5-8×10 10 CFU / ml in a volume ratio of 1-2:2-6 to form the functional bacterium A; Mix the above functional bacterium A bacterial liquid, the functional bacterium B bacterial liquid with a concentration of 5-7×10 9 CFU / ml, and the functional bacterium C bacterial liquid with a concentration of 2-6×10 10 CFU / ml in a volume ratio of 1-2:4-8:2-7; S2. Add nano-Fe 3 O 4 and the protective agent to the mixed bacterial liquid of the functional bacterium A, the functional bacterium B, and the functional bacterium C and mix evenly to form a bactericide, wherein the mass ratio of nano-Fe 3 O 4 in the compound bactericide is 0.1wt%-0.5wt%, and the mass ratio of the protective agent in the compound bactericide is 2wt%-5wt%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: The compound microbial inoculant of the present invention can rapidly promote the degradation of lignocellulose in straw in the soil, providing a basic source of material energy for the activities of soil microorganisms. At the same time, the corresponding microorganisms achieve the long-term sequestration of organic carbon through humus stabilization and mineral-associated organic carbon (MAOC) stabilization, and significantly enhance the efficiency of organic carbon sequestration through nano-Fe 3 O 4 ionization.

[0015] Under the synergistic action of each strain in this inoculant, it can effectively reduce the carbon loss during straw returning to the field, improve the carbon sequestration capacity of the soil, and increase the content of organic carbon in the soil. Brief Description of the Drawings

[0016] Figure 1 is a schematic diagram of the working process of this inoculant; Among them: Bacterium A: Functional bacterium A, Bacterium B: Functional bacterium B, Bacterium C: Functional bacterium C, where Fe 3+ is nano-Fe 3 O 4 ionizes. Detailed Embodiments

[0017] The present invention will be further described below in conjunction with specific embodiments.

[0018] The principle of this inoculant in straw treatment is as Figure 1 shown.

[0019] Bacillus subtilis ( Bacillus subtilis ) was deposited at the China General Microbiological Culture Collection Center (CGMCC) on December 14, 2022, with the deposit number: CGMCC.NO.26196, and the deposit address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

[0020] Bacillus licheniformis ( Bacillus licheniformis ) was deposited at the China General Microbiological Culture Collection Center (CGMCC) on December 14, 2022, with the deposit number: CGMCC.NO.26194, and the deposit address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

[0021] Pseudomonas aeruginosa ( Pseudomonas aeruginosa ) was deposited at the China General Microbiological Culture Collection Center (CGMCC) on December 14, 2022, with the deposit number: CGMCC.NO.26195, and the deposit address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

[0022] Trichoderma longibrachiatum ( Trichoderma longiflorum)(On December 14, 2022, it was deposited in the China General Microbiological Culture Collection Center (CGMCC), deposit number: CGMCC.NO.40444, and the deposit address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.)

[0023] Case Group 1 Example 1: Functional bacteria A include Bacillus subtilis (deposit number CGMCC.NO.26196) and Bacillus licheniformis (deposit number CGMCC.NO.26194). The composition of the special fermentation medium A for functional bacteria A is as follows: sodium carboxymethylcellulose 20 g / L, ammonium sulfate 2 g / L, dipotassium hydrogen phosphate 1 g / L, magnesium sulfate 0.5 g / L, calcium chloride 1 g / L, manganese sulfate 0.05 g / L, ferrous sulfate 0.05 g / L, pH 6 - 7.0. Bacillus subtilis with deposit number CGMCC.NO.26196 and Bacillus licheniformis with deposit number CGMCC.NO.26194 were respectively cultured in medium A to a concentration of 5.2×10 10 CFU / ml, 6.8×10 10 CFU / ml.

[0024] Functional bacteria B is Pseudomonas aeruginosa (deposit number CGMCC.NO.26195). The composition of the special fermentation medium B for functional bacteria B is as follows: sodium carboxymethylcellulose 20 g / L, dipotassium hydrogen phosphate 2 g / L, ammonium sulfate 1.4 g / L, magnesium sulfate heptahydrate 0.6 g / L, calcium chloride 0.3 g / L; pH is 6.5. Pseudomonas aeruginosa with deposit number CGMCC.NO.26195 was cultured in medium B to a concentration of 5.9×10 9 CFU / ml.

[0025] Functional bacteria C is Trichoderma longibrachiatum (deposit number CGMCC.NO.40444). The composition of the special fermentation medium C (spore amplification medium) for functional bacteria C is as follows: potato leachate 200 g / L, dipotassium hydrogen phosphate 2 g / L, sodium carboxymethylcellulose 20 g / L, guaiacol 0.1 g / L, pH 6. Trichoderma longibrachiatum with deposit number CGMCC.NO.40444 was cultured in medium C to a concentration of 2.2×10 10 CFU / ml.

[0026] The preparation of the compound microbial agent is as follows: S1. The bacterial liquid of Bacillus subtilis (deposit number CGMCC.NO.26196) with a concentration of 5.2×10 10 CFU / ml and the bacterial liquid of Bacillus licheniformis (deposit number CGMCC.NO.26194) with a concentration of 6.8×10 10 CFU / ml were mixed in a volume ratio of 1:2 to form functional bacteria A.

[0027] Mix the above-mentioned functional bacteria A bacterial solution, functional bacteria B bacterial solution with a concentration of 5.9×10 9 CFU / ml, and functional bacteria C bacterial solution with a concentration of 2.2×10 10 CFU / ml according to a volume ratio of 1:4:6.

[0028] By mass, uniformly mix 20% glycerol, 10% sucrose, 2% sodium alginate, 1% sodium chloride, and 67% deionized water to form a protective agent.

[0029] S2. Add nano-Fe 3 O 4 (average particle size 100 nm), the protective agent to the mixed bacterial solution of the above-mentioned functional bacteria A, functional bacteria B, and functional bacteria C, and mix evenly to form a composite bacterial agent, where nano-Fe 3 O 4 accounts for 0.3% by mass in the composite bacterial agent, and the protective agent accounts for 5% by mass in the composite bacterial agent.

[0030] Select the "rice-oil rotation" double-cropping planting area of Zhejiang Changnian. Divide the experimental plots. The size of the experimental plots is 6m×6m. Leave a 1m-wide isolation belt between the treatments in each experimental plot to prevent the spread and pollution of the bacterial agent. The field environment is 5-15°C. When the harvester harvests the crops, synchronously crush the straw and evenly cover it on the flat open space at the field edge. Mix the composite bacterial agent and water evenly according to a mass ratio of 3:100. The application rate of the composite bacterial agent is 3 kg / mu. Spray the mixture of the composite bacterial agent and water evenly on the surface of the field straw. The straw enters the plough layer about 15 cm deep with the operation of the rotary tiller. Randomly take soil samples in each block on the 30th day and measure the parameters as shown in Table 1. Randomly take soil samples on the 90th day and measure the parameters as shown in Table 2. The initial soil background value of the experimental plot is shown in Table 3.

[0031] At the same time, add a control group. For convenience of viewing, the control group, the above-mentioned Example 1, etc. are correspondingly named Treatment 1, Treatment 2, etc. as follows: Among them, Treatment 1: The difference from the straw returning treatment in Example 1 is that no microbial agents or auxiliary materials are added in this example. Treatment 2: That is, the straw returning scheme in Example 1. Treatment 3: The difference from the straw returning treatment in Example 1 is that the composite microbial agent does not contain Bacillus subtilis (deposit number CGMCC.NO.26196). Treatment 4: The difference from the straw returning treatment in Example 1 is that the composite microbial agent does not contain Bacillus licheniformis (deposit number CGMCC.NO.26194). Treatment 5: The difference from the straw returning treatment in Example 1 is that Pseudomonas aeruginosa in the composite microbial agent is directly purchased from the market. Treatment 6: The difference from the straw returning treatment in Example 1 is that the composite microbial agent does not contain Trichoderma longibrachiatum (deposit number CGMCC.NO.40444). Treatment 7: The difference from the straw returning treatment in Example 1 is that the composite microbial agent does not contain nano Fe 3 O 4 . Treatment 8: The difference from the straw returning treatment in Example 1 is that Trichoderma longibrachiatum in the composite microbial agent is directly purchased from the market. Treatment 9: The difference from the straw returning treatment in Example 1 is that the straw treatment microbial agent produced by Guangdong Weiliwang Company is used.

[0032] Table 1

[0033] It can be seen from Table 1 that after culturing for 30 days in the field environment of 5-15 °C, the degradation rates of cellulose, hemicellulose and lignin and the enzyme activities of each treatment in Treatment 1 are significantly lower than those of other treatments, proving that the addition of each microbial agent can promote the degradation of lignocellulose in the field and the improvement of microbial enzyme activity to varying degrees. The degradation rates of each lignocellulose and microbial enzyme activities in Treatment 2 are significantly higher than those of other treatments or there is no significant difference. Except for peroxidase, all indexes of Treatments 3 and 4 are significantly lower than those of Treatment 2, proving that the components in Functional Bacteria A (composed of Bacillus subtilis deposit number CGMCC.NO.26196 and Bacillus licheniformis deposit number CGMCC.NO.26194) play an indispensable and important role in the degradation of lignocellulose and the improvement of related enzyme activities. The cellulose degradation rate of Treatment 5 has no significant difference from that of Treatment 2, but the degradation rates of hemicellulose and lignin and the xylanase enzyme activity are significantly lower than those of Treatment 2, proving that Functional Bacteria B (i.e., Pseudomonas aeruginosa deposit number CGMCC.NO.26195) has an irreplaceable role in the degradation and transformation of hemicellulose. Except for the cellulose degradation rate and polyphenol oxidase, all other indexes of Treatments 6 and 8 are significantly lower than those of Treatment 2, proving that Functional Bacteria C (i.e., Trichoderma longibrachiatum deposit number CGMCC.NO.40444) constitutes the functional integrity of the composite microbial agent. The cellulose degradation rate and cellulase enzyme activity of Treatment 7 have no significant difference from those of Treatment 2, and the degradation rates of hemicellulose, lignin, xylanase enzyme activity and peroxidase enzyme activity are significantly lower than those of Treatment 2, proving that nano Fe 3 O4 is not related to cellulose degradation and focuses more on hemicellulose and lignin degradation; at the same time, nano-Fe 3 O 4 significantly enhances the function of the composite microbial agent. The polyphenol oxidase activity of treatment 9 is significantly lower than that of treatment 2, and there is no significant difference in cellulase, xylanase, and peroxidase between treatment 9 and treatment 2, which proves that in practical applications, treatment 2 and the commercially available microbial agent have similar effects on enhancing the enzyme activity in the soil; however, the degradation rates of various lignocelluloses in treatment 9 are significantly lower than those in treatment 2. In summary, each component in treatment 2 plays an irreplaceable and important role in the efficiency and integrity of the function; at the same time, the composite microbial agent of the present invention is applicable to the composting treatment of cold-region straw, and the composting application effect is better than that of treatment 9 (i.e., the commercially available microbial agent).

[0034] Table 2

[0035] Table 3

[0036] As can be seen from Table 2 and Table 3, there are basically no significant differences in soil organic carbon SOC, mineral-bound carbon MAOC, particulate organic carbon POC, and total humus in treatment 1 compared with the indicators in treatments 3, 4, 6, and 7; however, the dissolved organic carbon DOC and soil microbial biomass carbon MBC in treatment 1 are significantly lower than those in other treatments, which proves that the addition of the microbial agent can improve the biochemical metabolism degree of the soil to varying degrees, but due to the complexity of carbon turnover and the diversity of humus transformation, treatments 3, 4, 6, and 7 have not achieved the fixation and geographical improvement of organic carbon in the soil. The indicators of treatment 2 are higher than those of other treatments, which also proves the indispensability of each component in the composite microbial agent of the present invention. The soil organic carbon SOC in treatments 5 and 8 is significantly higher than that in treatments 1, 3, 4, 6, and 7, but significantly lower than that in treatment 2; at the same time, the dissolved organic carbon DOC and soil microbial biomass carbon MBC are significantly higher than those in treatments 3, 4, 6, and 7 but significantly lower than those in treatment 2, which indicates that by replacing Pseudomonas aeruginosa and Trichoderma longibrachiatum, the biochemical metabolism degree of the soil can be improved to a certain extent, thereby enhancing the soil's carbon sequestration ability, but the carbon sequestration effect is not as good as that of this composite microbial agent; each component in the composite microbial agent of the present invention is irreplaceable. The mineral-bound carbon MAOC, dissolved organic carbon DOC, and soil microbial biomass carbon MBC in treatment 9 are significantly higher than those in treatment 1, but the soil organic carbon SOC, particulate organic carbon POC, and total humus have no significant difference from those in treatment 1 and are significantly lower than those in treatment 2, which proves that although the commercially available microbial agent can improve the activity of microorganisms in the soil, it does not have the function of realizing soil carbon sequestration. Each component in the composite microbial agent of the present invention is indispensable and irreplaceable, and the integrity of the components is the fundamental guarantee for the composite microbial agent to exhibit excellent soil carbon sequestration ability.

[0037] Early rice was planted in the above experimental plots. The early rice was harvested in July, and rice samples were taken for index detection, as shown in Table 4.

[0038] Table 4

[0039] As can be seen from Table 4, there were no significant differences in the number of grains per panicle among the treatments. This index may depend on the rice variety, and at the same time, it also makes the seed setting rate, 1000-grain weight and yield of each treatment comparable. The effective panicle number, seed setting rate and 1000-grain weight of Treatment 2 were significantly higher than those of other treatments or had no significant differences, which proved that Treatment 2 had different degrees of promotion in all aspects of rice grain setting and development; the yield of Treatment 2 was significantly higher than that of other treatments, which also proved that Treatment 2 could improve soil fertility by optimizing the carbon sequestration process after straw entered the soil, thereby increasing rice yield. At the same time, the yields of Treatments 3, 4, 6 and 7 were significantly lower than that of Treatment 2, indicating that the lack of components in the compound bacterial agent of the present invention would affect all aspects of rice grain setting and development, resulting in a final yield lower than that of Treatment 2. The yield of Treatment 5 had no significant difference from that of Treatment 1, and the yields of Treatments 8 and 9 were significantly higher than that of Treatment 1 but significantly lower than that of Treatment 2, which proved that the replacement of Pseudomonas aeruginosa and Trichoderma longibrachiatum in the compound bacterial agent of the present invention did not ultimately achieve a better yield effect than Treatment 2. The yield of Treatment 9 was significantly higher than that of Treatment 1 but significantly lower than that of Treatment 2, which also proved that the commercially available bacterial agent could also increase the yield to a certain extent but was lower than the compound bacterial agent of the present invention. At the same time, Treatment 2 had the best yield improvement performance among all treatments.

[0040] The above is only the preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A composite bacterial agent for coupling straw decomposition and soil carbon fixation, characterized in that: include: Functional bacteria A, including: Bacillus subtilis with a preservation number of CGMCC.NO.26196 and Bacillus licheniformis with a preservation number of CGMCC.NO.26194, and the volume ratio of the two liquids is 1-2:2-6; Functional bacteria B, the functional bacteria B is Pseudomonas aeruginosa with the accession number CGMCC.NO.26195 Functional bacteria C, wherein the functional bacteria C is Trichoderma longipes with a preservation number of CGMCC.NO.40444; Protective agents, and Nano-Fe3O4; Among them, the liquid volume ratio of the functional bacteria A, functional bacteria B and functional bacteria C is 1-2:4-8:2-7, the proportion of nano Fe3O4 in the composite bacterial agent is 0.1wt%-0.5wt%, and the proportion of the protective agent in the composite bacterial agent is 2wt%-5wt%.

2. The composite bacterial agent for coupling straw decomposition and soil carbon fixation as claimed in claim 1, characterized in that: The concentrations of Bacillus subtilis and Bacillus licheniformis in the functional bacteria A are 4-6×10 10 CFU / ml, 5-8×10 10 CFU / ml, the concentrations of the functional bacteria B and the functional bacteria C were 5-7×10 9 CFU / ml, 2-6×10 10 CFU / ml.

3. The composite bacterial agent for coupling straw decomposition and soil carbon fixation as claimed in claim 1, characterized in that: In terms of mass, the protective agent includes 10-20wt% glycerol, 10-15wt% sucrose, 1-2wt% sodium alginate, 1-3wt% sodium chloride, and the remainder is deionized water.

4. The method for preparing the composite bacterial agent according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, the concentration is 4-6×10 10 CFU / ml of Bacillus subtilis liquid with the deposit number of CGMCC.NO.26196 and a concentration of 5-8×10 10 CFU / ml of Bacillus licheniformis with the deposit number of CGMCC.NO.26194, mixed in a volume ratio of 1-2:2-6 to form functional bacteria A; The functional bacteria A liquid with a concentration of 5-7×10 9 Functional bacteria B solution with a concentration of 2-6×10 CFU / ml 10 The functional bacteria C solution with CFU / ml was mixed in a volume ratio of 1-2:4-8:2-7; S2. Add nano-Fe3O4 and a protective agent to the mixed bacterial solution of the functional bacteria A, functional bacteria B, and functional bacteria C and mix them evenly to form a composite bacterial agent, wherein the nano-Fe3O4 accounts for 0.1wt%-0.5wt% of the composite bacterial agent, and the protective agent accounts for 2wt%-5wt% of the composite bacterial agent.

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