Composite biological stimulant aiming at tropical rainforest soil carbon improvement as well as preparation method and application of composite biological stimulant

Abstract

The invention relates to the technical field of soil carbon improvement, and discloses a composite biological stimulant for tropical rainforest soil carbon improvement and a preparation method and application thereof, the composite biological stimulant is obtained by mixing a microbial preparation, an immobilized carrier, porous biochar, an inorganic mineral compound, a slow release fertilizer, a soil conditioner and a plant symbiotic inoculant; the microbial preparation comprises one or more of lactic acid bacteria, nitrifying bacteria, phosphate solubilizing bacteria, nitrogen-fixing bacteria and arbuscular mycorrhizal fungi; the inorganic mineral compound comprises feldspar, apatite and montmorillonite; the slow-release fertilizer comprises biochar, humic acid and phosphate; the soil conditioner comprises biological colloid prepared from seaweed extract and natural plant fiber prepared from straw and palm fiber; the plant symbiotic inoculant comprises rhizobium and / or endophyte. According to the composite biological stimulant, the soil carbon fixing capacity of the tropical rainforest is remarkably improved, the soil void structure is improved, and the plant growth capacity is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of soil carbon enhancement, and more particularly, to a composite biostimulant for enhancing soil carbon in tropical rainforests, its preparation method and application. Background Art

[0002] Tropical rainforests cover about 6% of the global land area, yet store more than half of the world's forest carbon and have extremely high biodiversity. For the soil carbon cycle, the turnover process of soil microorganisms is an important driving force for the formation of organic matter. Microbial residues participate in and regulate the carbon turnover and stabilization process in the soil, which is the main way for the formation of soil organic carbon.

[0003] However, the soils in tropical rainforests are usually red soils or yellow soils, which have low nutrient content and high acidity, restricting the growth of plants and the long-term stable storage of soil carbon. At the same time, due to the high-temperature and high-humidity climate conditions, the decomposition rate of soil organic matter in tropical rainforests is very fast, reducing the soil's carbon storage and stabilization capacity. Summary of the Invention

[0004] In view of this, the present invention provides a composite biostimulant for enhancing soil carbon in tropical rainforests, its preparation method and application, aiming to solve the problem of low soil organic carbon and fast decomposition in current tropical rainforest soils.

[0005] On the one hand, a composite biostimulant for enhancing soil carbon in tropical rainforests proposed by the present invention is obtained by mixing a microbial preparation, an inorganic mineral complex, a slow-release fertilizer, a soil conditioner and a plant symbiotic inoculant;

[0006] The microbial preparation includes one or more of lactic acid bacteria, nitrifying bacteria, phosphorus-solubilizing bacteria, nitrogen-fixing bacteria and arbuscular mycorrhizal fungi; the inorganic mineral complex includes feldspar, apatite and montmorillonite; the slow-release fertilizer includes biochar, humic acid and phosphate; the soil conditioner includes a biocolloid prepared from seaweed extract and natural plant fibers prepared from bamboo fibers and palm fibers; the plant symbiotic inoculant includes rhizobia and / or endophytes.

[0007] Preferably, the composite biostimulant includes the following components in parts by weight:

[0008] In the microbial preparation, 0.1 - 2 parts of lactic acid bacteria, 0.1 - 2 parts of nitrifying bacteria, 0.1 - 2 parts of phosphorus-solubilizing bacteria, 0.1 - 2 parts of nitrogen-fixing bacteria, 1 - 3 parts of arbuscular mycorrhizal fungi;

[0009] In the inorganic mineral complex, 10.1 - 20 parts of feldspar, 5 - 10 parts of apatite, 5 - 10 parts of montmorillonite;

[0010] In the slow-release fertilizer, there are 15 - 25 parts of biochar, 5 - 10 parts of humic acid, and 5 - 10 parts of phosphate. The phosphate is calcium dihydrogen phosphate and calcium hydrogen phosphate;

[0011] In the soil conditioner, there are 2 - 5 parts of bio-colloid and 5 - 10 parts of natural plant fiber;

[0012] The plant symbiotic inoculant is 0.1 - 2 parts of rhizobia and 0.1 - 2 parts of endophytes.

[0013] Preferably, the biochar is prepared by carbonizing rice husks or bamboo and has a specific surface area > 300 m 2 / g;

[0014] The phosphate is less than 300 mesh, and the addition ratio of calcium dihydrogen phosphate to calcium hydrogen phosphate in the phosphate is 1:1;

[0015] The addition ratio of bamboo fiber to palm fiber in the natural plant fiber is 1:0.7 - 1.

[0016] On the other hand, the present invention also provides a preparation method of the above composite biostimulant for carbon enhancement of tropical rainforest soil, including the following steps:

[0017] Inoculate lactic acid bacteria strains into the sterilized MRS medium and perform anaerobic fermentation culture at 37°C for 48 hours; culture nitrifying bacteria in the nitrifying bacteria medium and perform constant temperature culture at 30°C for 72 hours; culture phosphate-solubilizing bacteria in the Pikovskaya medium and perform constant temperature culture at 37°C for 48 hours; inoculate nitrogen-fixing bacteria into the semi-solid nitrogen inorganic medium and culture at 28 - 30°C for 72 hours; culture arbuscular mycorrhizal fungi in the environment of plant root symbiosis, using sterile sandy soil as the substrate, and the culture period is 6 - 8 weeks;

[0018] Select one or more of the lactic acid bacteria, nitrifying bacteria, phosphate-solubilizing bacteria, nitrogen-fixing bacteria, and arbuscular mycorrhizal fungi according to weight parts and obtain a microbial preparation through mixing;

[0019] Add a mixed solution of konjac glucomannan, sodium alginate, and the microbial preparation to the PBS buffer solution, and then gradually add a CaCl2 solution and mechanically stir under the condition of 20 - 30 r / min; the addition amount of konjac glucomannan is 1 weight part; the addition amount of sodium alginate is 1 - 2 weight parts;

[0020] Crush feldspar, apatite, and montmorillonite respectively, roast feldspar, and perform acid leaching on apatite and montmorillonite; mix the treated feldspar, apatite, and montmorillonite evenly according to a ratio to obtain an inorganic mineral complex;

[0021] Carbonize rice husks and / or bamboo in an inert environment at 500 - 600 °C for 2 - 3 hours. After cooling to room temperature, crush them to a specific surface area > 300 m 2 / g to obtain biochar; mix the biochar, phosphate, and humic acid to obtain a slow-release fertilizer;

[0022] Add microbial agents, inorganic mineral complexes, slow-release fertilizers, soil conditioners, and plant symbiotic inoculants in proportion, and use mechanical stirring or drum mixing equipment to mix them evenly to obtain a composite biostimulant.

[0023] The MRS medium, also known as Moraxella media, mainly consists of: peptone, yeast extract, glucose, trisodium citrate, sodium acetate, and antibiotics.

[0024] The PBS buffer solution is a phosphate buffer solution, mainly composed of sodium dihydrogen phosphate (NaH2PO4), disodium hydrogen phosphate (Na2HPO4), and sodium chloride (NaCl).

[0025] Preferably, the nitrifying bacteria medium is prepared by the following method:

[0026] Mix 1.0 g of ammonium sulfate, 5.0 g of calcium carbonate, 1.0 g of potassium dihydrogen phosphate, 0.5 g of magnesium sulfate, 0.5 g of sodium chloride, and 1000 mL of water, and adjust the pH to 7.5 - 8.0 with hydrochloric acid or sodium hydroxide.

[0027] Preferably, the feldspar is crushed to 100 - 200 mesh and calcined at 800 °C for 2 hours; the apatite is crushed to less than 200 mesh and then soaked in 5% phosphoric acid solution for 30 min and dried; the montmorillonite is crushed to 100 - 300 mesh, dried at 70 °C for 24 hours, and soaked in 1% hydrochloric acid solution for 2 h.

[0028] Preferably, the soil conditioner is prepared by the following method:

[0029] Select brown algae as the raw material, perform cold extraction with water at 10 - 15 °C for 3 hours, filter and concentrate to obtain a bio-colloid; select bamboo fiber and palm fiber and mix them in proportion, cook at 100 °C for 1 hour, and crush to a fiber length of 0.5 - 1.0 cm to obtain the soil conditioner.

[0030] Preferably, the symbiotic inoculant is cultured by the following method:

[0031] Select rhizobia and perform fermentation culture in a rhizobia medium at a temperature of 28 - 30 °C for 72 h; select endophytes and perform co-culture in a medium containing plant roots at a culture temperature of 25 - 28 °C for 4 - 6 weeks;

[0032] Mix rhizobia and / or endophytes in proportion to obtain a symbiotic inoculant.

[0033] Preferably, the rhizobia medium comprises: 10 g of D-mannitol, 0.5 g of yeast extract, 2 g of soybean hydrolyzate, 0.5 g of chitosan oligosaccharide, 1 g of malic acid, 0.5 g of potassium dihydrogen phosphate, 0.2 g of magnesium sulfate heptahydrate, 0.05 g of ferrous sulfate heptahydrate, 0.1 g of calcium chloride, 15 - 20 g of agar, and 5 mL of rice straw extract;

[0034] Dissolve each component in the rhizobia medium in distilled water and heat until the agar is completely dissolved. Adjust the pH of the medium to 6.8 - 7.0 using 0.1 M HCl or NaOH; heat to 121 °C and maintain for 15 - 20 min, then cool to room temperature to obtain the rhizobia medium.

[0035] The present invention also protects the application of the above-mentioned composite biostimulant for enhancing soil carbon in tropical rainforests in enhancing the soil carbon sequestration capacity of tropical rainforests.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] The composite biostimulant of the present invention, through the introduction of microbial agents such as lactic acid bacteria, nitrifying bacteria, phosphate-solubilizing bacteria, and nitrogen-fixing bacteria, not only directly participates in the carbon cycle in the soil, but also significantly improves the soil carbon cycle efficiency by promoting the decomposition, transformation, nitrogen cycle, and phosphorus dissolution of organic matter. Arbuscular mycorrhizal fungi particularly increase the absorption capacity of plant roots, enabling carbon to be fixed in the roots. The feldspar, apatite, and montmorillonite in the inorganic mineral complex cooperate with each other, enhancing both the structural stability of the soil and its water retention and nutrient adsorption capacities. This structure contributes to the long-term stability of soil organic carbon. The biochar, humic acid, and phosphate in the slow-release fertilizer are used in combination, enabling nutrients to be released slowly and continuously, avoiding the problem of nutrient waste caused by short-term large-scale fertilization. The biochar further improves the soil carbon stabilization capacity through its large specific surface area, while the phosphate provides phosphorus in a stable form to meet the long-term growth needs of plants. The combination of the biocolloid prepared from seaweed extract and natural plant fibers in the soil conditioner not only improves the physical structure of the soil, but also provides an excellent living environment for soil microorganisms. The polysaccharide structure of the biocolloid provides energy for microorganisms, while the plant fibers are gradually decomposed as a carbon source, continuously providing nutrients for microbial activities. The rhizobia and endophytes in the plant symbiotic inoculant significantly enhance the nitrogen fixation and nutrient absorption capacities of plants through their symbiotic relationship with plant roots. Especially in a complex ecosystem such as the tropical rainforest, this symbiotic relationship helps improve the plant's adaptability to the soil, while enhancing the carbon fixation and stabilization effects of the soil. The microbial agent and the inorganic mineral complex act together to enhance the plant's soil carbon stabilization capacity, while improving the soil environment and increasing the soil carbon cycle efficiency. Detailed implementation mode

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] In the following examples, the MRS medium was purchased from Qingdao Haibo Biotechnology (product number: HB0384-51), and the Pikovskaya medium was purchased from Shanghai Zeye Biotechnology Co., Ltd. (product number: ZY6MM5051).

[0040] Example 1: Influence of the composite biostimulant on the carbon fixation and stabilization capacities of tropical rainforest soil

[0041] Experimental steps:

[0042] Microbial agent: 1.3 parts of lactic acid bacteria, 0.8 parts of nitrifying bacteria, 1.1 parts of phosphate-solubilizing bacteria, 1.7 parts of nitrogen-fixing bacteria and 2 parts of arbuscular mycorrhizal fungi are cultured separately and then mixed. The specific operations include:

[0043] The lactic acid bacteria are anaerobically fermented and cultured at 37°C for 48 hours;

[0044] The nitrifying bacteria are cultured at a constant temperature of 30°C for 72 hours;

[0045] The phosphate-solubilizing bacteria are cultured at a constant temperature of 37°C for 48 hours;

[0046] The nitrogen-fixing bacteria are cultured at 30°C for 72 hours;

[0047] The arbuscular mycorrhizal fungi are symbiotically cultured with plant roots in sterile sandy soil for 8 weeks;

[0048] Subsequently, konjac glucomannan, sodium alginate and the mixed solution of the microbial agent are added to the PBS buffer solution, and then the CaCl2 solution is added drop by drop, and mechanical stirring is carried out under the condition of 20 - 30 r / min; the addition amount of the konjac glucomannan is 1 part by weight; the addition amount of the sodium alginate is 1 part by weight; the volume concentration of the konjac glucomannan and the sodium alginate in the system is 3 - 5%.

[0049] Among them, the volume concentration of the CaCl2 solution in the system is 8 - 10%.

[0050] Inorganic mineral complex: Feldspar is crushed to about 150 meshes and calcined at 800°C for 2 hours, apatite is crushed to 200 meshes, soaked in 5% phosphoric acid solution for 30 minutes and dried, montmorillonite is crushed to 200 meshes and then dried at 70°C for 24 hours and soaked in 1% hydrochloric acid solution for 2 hours, and finally the treated minerals are mixed in proportion.

[0051] Among them, there are 14 parts of feldspar, 9 parts of apatite and 7 parts of montmorillonite.

[0052] Slow-release fertilizer: Rice husk is carbonized in an inert environment at 550°C for 3 hours and then crushed to a specific surface area > 300 m 2 / g, and then mixed evenly with phosphate (a 1:1 mixture of calcium dihydrogen phosphate and calcium hydrogen phosphate) and humic acid.

[0053] In this example, there are 19 parts of biochar, 6 parts of humic acid, 3 parts of calcium dihydrogen phosphate and 3 parts of calcium hydrogen phosphate in the slow-release fertilizer.

[0054] Soil conditioner: Brown algae is extracted in water at 15°C for 3 hours and then filtered and concentrated to obtain a biological colloid. Bamboo fiber and palm fiber are mixed in proportion and steamed at 100°C for 1 hour and then crushed to a fiber length of 0.5 cm.

[0055] In this embodiment, the bio-colloid in the soil conditioner is 4 parts and the natural plant fiber is 8 parts.

[0056] Plant symbiotic inoculant: Rhizobia are cultured at 30 °C for 72 hours, and endophytes are co-cultured with plant roots for 6 weeks, and then the two are mixed in proportion.

[0057] In this embodiment, the rhizobia are 1 part and the endophytes are 2 parts.

[0058] All components are mixed evenly in proportion to prepare a composite biostimulant.

[0059] Experimental design:

[0060] Typical infertile soil in the tropical rainforest is selected and evenly divided into two groups: a control group (without applying the composite biostimulant) and an experimental group (applying the composite biostimulant, 50 g per square meter).

[0061] The same number of tropical native plants Hopea exalata are planted, 20 plants in each group. They are cultivated under the same environmental conditions, and the soil organic carbon and plant growth conditions are measured after 3 months.

[0062] Experimental results:

[0063] Soil organic carbon (unit: g / kg): 15.2 g / kg in the control group and 21.8 g / kg in the experimental group. Plant growth conditions (unit: cm): The average height in the control group is 45 cm, and the average height in the experimental group is 58 cm.

[0064] Conclusion:

[0065] The experimental results show that the soil organic carbon of the soil applied with the composite biostimulant is significantly higher than that of the control group without application, indicating that the composite biostimulant effectively improves the soil organic carbon. At the same time, the growth conditions of the plants are also significantly improved, proving that the stimulant also has a promoting effect on plant growth.

[0066] Example 2: Effect of the composite biostimulant on soil structure improvement

[0067] Experimental steps:

[0068] Prepare the composite biostimulant according to the same steps and ratios in Example 1.

[0069] Experimental design:

[0070] Select infertile soil in the tropical rainforest and evenly divide it into two groups: a control group (without applying the composite biostimulant) and an experimental group (applying the composite biostimulant, 50 g per square meter). Measure the physical properties such as water retention capacity, porosity, and particle composition of the two groups of soils respectively. Cultivate the same number and types of plants and observe the influence of soil structure on plant growth.

[0071] Experimental results:

[0072] Soil water retention capacity (unit: %): 32% for the control group and 45% for the experimental group.

[0073] Soil porosity (unit: %): 40% for the control group and 55% for the experimental group.

[0074] Plant growth status (unit: cm): The average height of the control group is 40 cm, and the average height of the experimental group is 52 cm.

[0075] Conclusion:

[0076] The water retention capacity and porosity of the soil in the experimental group are significantly better than those in the control group, indicating that the composite biostimulant has a significant effect on improving soil structure. At the same time, the improved soil is conducive to plant growth, further verifying the effectiveness of the composite biostimulant.

[0077] In summary, the embodiments of the present invention can improve the soil carbon fixation and stabilization ability:

[0078] The use of microbial agents (lactic acid bacteria, nitrifying bacteria, phosphate-solubilizing bacteria, nitrogen-fixing bacteria, arbuscular mycorrhizal fungi) is the key. These microorganisms play multiple roles in the soil:

[0079] Lactic acid bacteria produce lactic acid through fermentation, regulate the pH value of the soil, inhibit the growth of harmful microorganisms, and at the same time promote the decomposition and transformation of soil organic carbon. Nitrifying bacteria convert ammonia in the soil into nitrate, which not only enhances the nitrogen cycle but also indirectly promotes soil carbon fixation. Phosphate-solubilizing bacteria can convert insoluble phosphates into forms that can be absorbed by plants, improve the utilization rate of phosphorus, and support carbon fixation during plant growth. Nitrogen-fixing bacteria fix nitrogen in the air into the soil, provide available nitrogen sources for plants, reduce the dependence on chemical fertilizers, and effectively increase the organic carbon in the soil. Arbuscular mycorrhizal fungi increase the ability of plants to absorb nutrients and water through the symbiotic underground network established with plant roots. Especially in the infertile soils of tropical rainforests, they improve the growth efficiency of plants, thereby increasing and stabilizing soil organic carbon. These microorganisms form a virtuous cycle in the soil through their interactions, enhancing and stabilizing soil organic carbon.

[0080] Comprehensive soil remediation and improvement effect:

[0081] The scientific combination of each component makes the composite biostimulant show superiority in many aspects: the combination of feldspar and montmorillonite not only improves the soil structure stability, but also enhances its water retention and nutrient retention capabilities. The combination of biochar and humic acid effectively increases the soil organic carbon and ensures the continuous growth of plants by slowly releasing nutrients. The combined action of microbial agents and plant symbiotic inoculants significantly enhances the diversity and activity of the soil microbial community and promotes the biological processes in the carbon cycle. The synergistic effect of these components not only increases and stabilizes the soil organic carbon, but also improves the physical, chemical and biological properties of the soil, making the soil more adaptable to the complex ecological conditions of the tropical rainforest, thus achieving an overall improvement in soil quality.

[0082] Konjac glucomannan and sodium alginate can form a gel network structure under the action of calcium ions (CaCl2). This gel network encapsulates the microbial agent, forming an immobilized microbial carrier. The three-dimensional network structure of the gel provides a relatively stable microenvironment for the survival of microorganisms, protecting them from the drastic changes in the external environment (such as fluctuations in temperature, humidity, pH value in the soil, as well as competition and predation by other microorganisms), which is conducive to the microorganisms maintaining their activity and continuously playing their roles for a long time. For example, in the variable climate and complex soil ecological environment of the tropical rainforest, the immobilized microorganisms can better adapt to environmental changes, rather than being easily inactivated like free microorganisms. The gel network structure formed by konjac glucomannan and sodium alginate can serve as a physical barrier. The microorganisms are encapsulated inside the gel, and the release rate of their metabolites (such as enzymes, organic acids, etc.) and the microorganisms themselves into the external environment will be restricted by the gel network. This avoids the rapid release and subsequent rapid consumption or inactivation of active substances such as enzymes in a short period of time, achieving a slow-release effect and increasing the continuous action time of the biostimulant.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A composite biostimulant for enhancing soil carbon in tropical rainforests, characterized in that, It is obtained by mixing a microbial agent, an inorganic mineral complex, a slow-release fertilizer, a soil conditioner and a plant symbiotic inoculant; The microbial agent includes one or more of lactic acid bacteria, nitrifying bacteria, phosphate-solubilizing bacteria, nitrogen-fixing bacteria and arbuscular mycorrhizal fungi; the inorganic mineral complex includes feldspar, apatite and montmorillonite; the slow-release fertilizer includes biochar, humic acid and phosphate; the soil conditioner includes a biocolloid prepared from seaweed extract and natural plant fibers prepared from rice straw and palm fibers; the plant symbiotic inoculant includes rhizobia and / or endophytes.

2. The composite biostimulant for enhancing soil carbon in tropical rainforests according to claim 1, wherein The composite biostimulant includes the following components in parts by weight: In the microbial agent, 0.1-2 parts of lactic acid bacteria, 0.1-2 parts of nitrifying bacteria, 0.1-2 parts of phosphate-solubilizing bacteria, 0.1-2 parts of nitrogen-fixing bacteria, and 1-3 parts of arbuscular mycorrhizal fungi; In the inorganic mineral complex, 10.1-20 parts of feldspar, 5-10 parts of apatite, and 5-10 parts of montmorillonite; In the slow-release fertilizer, 15-25 parts of biochar, 5-10 parts of humic acid, and 5-10 parts of phosphate, and the phosphate is calcium dihydrogen phosphate and calcium hydrogen phosphate; In the soil conditioner, 2-5 parts of biocolloid and 5-10 parts of natural plant fibers; The plant symbiotic inoculant is 0.1-2 parts of rhizobia and 0.1-2 parts of endophytes.

3. The composite biostimulant for enhancing tropical rainforest soil carbon according to claim 2, characterized in that, The biochar is prepared by carbonizing rice husks or bamboo and has a specific surface area > 300 m 2 / g; The phosphate is less than 300 mesh, and the addition ratio of calcium dihydrogen phosphate to calcium hydrogen phosphate in the phosphate is 1:1; The addition ratio of rice straw to palm fibers in the natural plant fibers is 1:0.7-1.

4. A preparation method of a composite biostimulant for enhancing soil carbon in tropical rainforests according to any one of claims 1-3, characterized in that, It includes the following steps: Inoculate the lactic acid bacteria strain into the sterilized MRS medium and carry out anaerobic fermentation culture at 37°C for 48 hours; culture the nitrifying bacteria in the nitrifying bacteria medium and carry out constant temperature culture at 30°C for 72 hours; culture the phosphate-solubilizing bacteria in the Pikovskaya medium and carry out constant temperature culture at 37°C for 48 hours; inoculate the nitrogen-fixing bacteria into the semi-solid nitrogen inorganic medium and culture at 28-30°C for 72 hours; culture the arbuscular mycorrhizal fungi in the environment of plant root symbiosis, use sterile sandy soil as the substrate, and the culture period is 6-8 weeks; Select the lactic acid bacteria, nitrifying bacteria, phosphate-solubilizing bacteria, nitrogen-fixing bacteria and arbuscular mycorrhizal fungi in parts by weight and mix them to obtain a microbial agent; Add konjac glucomannan, sodium alginate and the mixed solution of the microbial agent to the PBS buffer solution, and then dropwise add the CaCl2 solution and mechanically stir under the condition of 20-30 r / min; the addition amount of konjac glucomannan is 1 part by weight; the addition amount of sodium alginate is 1-2 parts by weight; Crush feldspar, apatite and montmorillonite respectively, roast the feldspar, and carry out acid leaching on apatite and montmorillonite; mix the treated feldspar, apatite and montmorillonite evenly according to the ratio to obtain an inorganic mineral complex; Carbonize rice husks and / or bamboo in an inert environment at 500 - 600 °C for 2 - 3 hours. After cooling to room temperature, crush it to a specific surface area > 300 m 2 / g to obtain biochar; mix the biochar, phosphate, and humic acid to obtain a slow-release fertilizer; Add the microbial agent, inorganic mineral complex, slow-release fertilizer, soil conditioner and plant symbiotic inoculant in proportion, and use a mechanical stirring or drum mixing device to mix them evenly to obtain a composite biostimulant.

5. The preparation method of the composite biostimulant for enhancing soil carbon in tropical rainforests according to claim 4, characterized in that, The nitrifying bacteria medium is prepared by the following method: 1.0 g of ammonium sulfate, 5.0 g of calcium carbonate, 1.0 g of potassium dihydrogen phosphate, 0.5 g of magnesium sulfate, 0.5 g of sodium chloride and 1000 mL of water are mixed, and the pH is adjusted to 7.5 - 8.0 with hydrochloric acid or sodium hydroxide.

6. The preparation method of the composite biostimulant for enhancing tropical rainforest soil carbon according to claim 4, characterized in that, The feldspar is crushed to 100 - 200 mesh and calcined at 800 °C for 2 hours; the apatite is crushed to less than 200 mesh and then soaked in 5% phosphoric acid solution for 30 min and dried; the montmorillonite is crushed to 100 - 300 mesh, dried at 70 °C for 24 hours, and soaked in 1% hydrochloric acid solution for 2 h.

7. The preparation method of the composite biostimulant for enhancing soil carbon in tropical rainforests according to claim 4, wherein The soil conditioner is prepared by the following method: Select brown algae as the raw material, perform cold extraction with water at 10 - 15 °C, the extraction time is 3 hours, and after filtration and concentration, a biological colloid is obtained; select rice straw and palm fiber and mix them in proportion, cook at 100 °C for 1 hour, and crush to a fiber length of 0.5 - 1.0 cm to obtain the soil conditioner.

8. The preparation method of the composite biostimulant for enhancing tropical rainforest soil carbon according to claim 4, characterized in that, The symbiotic inoculant is cultured by the following method: Select rhizobia and perform fermentation culture in a rhizobia medium at a temperature of 28 - 30 °C for 72 h; select endophytes and perform co-culture in a medium containing plant roots at a culture temperature of 25 - 28 °C for 4 - 6 weeks; Mix the rhizobia and / or endophytes in proportion to obtain the symbiotic inoculant.

9. The preparation method of the composite biostimulant for enhancing tropical rainforest soil carbon according to claim 8, characterized in that, The rhizobia medium includes: 10 g of D-mannitol, 0.5 g of yeast extract, 2 g of soybean hydrolyzate, 0.5 g of chitosan oligosaccharide, 1 g of malic acid, 0.5 g of potassium dihydrogen phosphate, 0.2 g of magnesium sulfate heptahydrate, 0.05 g of ferrous sulfate heptahydrate, 0.1 g of calcium chloride, 15 - 20 g of agar and 5 mL of rice straw extract; Dissolve each component in the rhizobia medium in distilled water and heat until the agar is completely dissolved, adjust the pH of the medium to 6.8 - 7.0 with 0.1 M HCl or NaOH; heat to 121 °C and maintain for 15 - 20 min, and then cool to room temperature to obtain the rhizobia medium.

10. Use of a composite biostimulant for enhancing carbon sequestration capacity of tropical rainforest soil according to any one of claims 1 - 8 in enhancing the carbon sequestration capacity of tropical rainforest soil.