Method for rapidly improving carbon sequestration performance of coastal saline-alkali soil by promoting formation of soil aggregates through MICP

Abstract

The invention discloses a coastal saline-alkali soil carbon sequestration performance rapid improvement method for promoting soil aggregate formation through MICP, and belongs to the field of coastal saline-alkali soil improvement and carbon sequestration. According to the method, urease-producing active functional bacteria liquid and cementing liquid are mixed to serve as soil carbon sequestration liquid; adding the soil carbon sequestration liquid into the to-be-treated coastal saline-alkali soil, adding an organic fertilizer, mixing, and keeping an aerobic environment; the urease-producing active functional bacteria decompose and activate urea and a calcium source in the cementing liquid, and calcium carbonate is formed by absorbing CO2 so as to bond saline-alkali soil particles and organic carbon to form a soil aggregate, so that the direct carbon sequestration performance of the soil is improved; meanwhile, formation of soil aggregates leads to evolution of physicochemical properties and dominant functional flora of the coastal saline-alkali soil, autotrophic carbon sequestration microorganisms are enriched, and the indirect carbon sequestration performance of the soil is further improved. According to the method, the number of coast saline-alkali soil aggregates and the carbon sequestration performance can be rapidly improved, carbon emission after organic fertilizer is applied is greatly reduced, and the method has important application value for improving coast saline-alkali soil and improving the carbon sequestration function of the coast saline-alkali soil.

Description

Technical Field

[0001] The present invention belongs to the field of coastal saline-alkali soil improvement and carbon sequestration, and particularly relates to a method for rapidly improving the carbon sequestration performance of coastal saline-alkali land by promoting the formation of soil aggregates by MICP. Background Art

[0002] The area of coastal wetlands accounts for less than 0.2% of the ocean area, but its carbon storage accounts for 50% of the ocean carbon (blue carbon) storage, and it is regarded as the main body of blue carbon. However, the organic matter content of coastal saline-alkali soil is generally less than 0.6%, far lower than that of healthy soil. Research shows that in a high-salt environment, when the sodium adsorption ratio (SAR) > 15, the proportion of water-stable aggregates > 0.25 mm in the soil decreases by 60% - 80%. Soil salinity (electrical conductivity > 8 dS / m) and pH value (8.5 - 9.6) inhibit plant growth, resulting in a vegetation coverage of less than 30%. The high-salt environment reduces the diversity of the soil microbial community, and the abundance of soil carbon-fixing bacteria (such as ammonia-oxidizing bacteria) decreases by 1 - 2 orders of magnitude.

[0003] Due to natural factors such as seawater intrusion, high groundwater level, and strong evaporation, coastal saline-alkali land generally has problems such as high soil salinity, compact structure, lack of organic matter, and low fertility, resulting in difficult vegetation growth, reduced microbial activity, and serious degradation of ecosystem functions. High-concentration sodium ions (Na + ) in saline-alkali soil cause the dispersion of soil colloids by replacing Ca 2+ and Mg 2+ in the soil colloid, leading to a decrease in the stability of soil aggregates. The destruction of aggregates exposes the originally physically protected organic matter to microbial decomposition, accelerating the mineralization of organic carbon into CO2 and reducing the soil carbon sink capacity.

[0004] Traditional saline-alkali soil improvement technologies, such as physical salt washing and application of organic fertilizers, have limitations such as high cost, long cycle, easy secondary pollution or carbon emissions, and are difficult to meet the coordinated needs of large-scale ecological restoration and carbon neutrality goals in coastal areas. Using the microbial-induced calcium carbonate precipitation technology to improve soil means that CO3 2- produced by microbial metabolism reacts with CaO in the cementing solution to form CaCO3, which cements soil particles to form stable aggregates. For the improvement of coastal saline-alkali soil, the increase in soil aggregates can not only improve the carbon sequestration performance of coastal saline-alkali land by promoting the mineral protection of organic matter and slowing down its biodegradation, but also accelerate the loss of Na + in coastal saline-alkali soil. Summary of the Invention

[0005] The purpose of the present invention is to solve the deficiencies of traditional saline-alkali soil improvement technologies and provide a method for rapidly improving the carbon sequestration performance of coastal saline-alkali land by promoting the formation of soil aggregates by MICP.

[0006] The specific technical solution adopted by the present invention is as follows:

[0007] The present invention provides a method for rapidly improving the carbon sequestration performance of coastal saline-alkali soil to promote the formation of soil aggregates. A urease-producing active functional bacteria solution and a cementing solution are mixed to serve as a soil carbon sequestration solution; the soil carbon sequestration solution is added to the coastal saline-alkali soil to be treated, and organic fertilizer is added and mixed to keep the coastal saline-alkali soil to be treated in an aerobic environment; the urease-producing active functional bacteria decompose and activate urea and calcium sources in the cementing solution, and form calcium carbonate by absorbing CO2 to cement saline-alkali soil particles and organic carbon to form soil aggregates, thereby improving the direct soil carbon sequestration performance, and improving the indirect soil carbon sequestration performance by in-situ enriching autotrophic carbon sequestration microorganisms.

[0008] Preferably, the urease-producing active functional bacteria is Bacillus subtilis; the Bacillus subtilis is preserved in the China Center for Type Culture Collection, with the preservation number of CCTCC·WB·2008694, the preservation date of November 15, 2006, and the address of the preservation unit being the China Center for Type Culture Collection, Wuhan University, Bayi Road, Wuchang District, Wuhan City, Hubei Province.

[0009] Preferably, the cementing solution includes urea, calcium chloride and NB nutrient broth; the urea content in the soil carbon sequestration solution is 0.4 - 0.6 mol / L, the calcium chloride content is 0.15 - 0.3 mol / L calcium chloride, and the NB nutrient broth content is 2 - 4 g / L.

[0010] Preferably, the OD 600 of the urease-producing active functional bacteria solution is 0.8 - 1.2.

[0011] Preferably, the addition amount of the urease-producing active functional bacteria solution in the soil carbon sequestration solution is 80 - 120 mL of the bacteria solution added to every 1000 g of saline-alkali soil.

[0012] Preferably, the addition amount of the organic fertilizer in the coastal saline-alkali soil to be treated is 240 - 260 g / kg.

[0013] Preferably, the application amount of the soil carbon sequestration solution is 1 - 3 L per square meter of soil.

[0014] Preferably, the coastal saline-alkali soil to be treated is plowed by a rotary tiller, and the soil carbon sequestration solution is sprayed while plowing; the number of times of plowing and spraying the soil carbon sequestration solution is 2 - 3 times.

[0015] Preferably, during the process of improving the carbon sequestration performance of the coastal saline-alkali soil to be treated, the temperature is controlled at 24 - 26 °C, the soil moisture content is 10% - 15%, and the carbon sequestration period is 10 - 90 days.

[0016] The present invention has the following beneficial effects compared with the prior art:

[0017] The present invention provides a method for rapidly improving the carbon sequestration performance of coastal saline-alkali soil. Through the synergistic effect of Bacillus subtilis and the cementing solution, the carbon sequestration ability of coastal saline-alkali soil can be significantly improved in a short time. The Bacillus subtilis used can tolerate high saline-alkali environments, survive and function efficiently in coastal saline-alkali soil; the cementing solution can rapidly form stable soil aggregates, reduce carbon decomposition and loss, and at the same time improve soil permeability and water retention.

[0018] In the present invention, Bacillus subtilis is used to decompose urea and calcium sources in the cementing solution to produce NH4 + and CO3 2- . CO3 2- and CaO in the cementing solution form CaCO3 minerals under the mediation of NH4 + and H2O. This mineral formation process can cement soil organic and inorganic particles, promote the rapid formation of soil aggregates, and enhance the direct carbon sequestration performance of the soil. In addition, the extracellular polymers secreted by Bacillus subtilis also contribute to the formation of soil aggregates. The increase in soil aggregates can also promote the protection of organic matter by minerals, slow down its biodegradation, promote the change of the physical and chemical properties of coastal saline-alkali soil and the evolution of dominant functional flora, and further enhance the indirect carbon sequestration performance of coastal saline-alkali soil by enriching autotrophic carbon sequestration microorganisms.

[0019] The method provided by the present invention has low cost and no secondary pollution, can achieve rapid and efficient carbon sequestration effects, and provides an effective technical means for the ecological restoration and carbon emission reduction of coastal saline-alkali soil. Specific Embodiments

[0020] The following further elaborates and explains the present invention in combination with specific embodiments. The technical features of each embodiment in the present invention can be combined accordingly without mutual conflict.

[0021] In the following examples, the urease-producing functional bacteria used are all Bacillus subtilis; this Bacillus subtilis is preserved in the China Center for Type Culture Collection, with the preservation number CCTCC·WB·2008694, the preservation date being November 15, 2006, and the address of the preservation unit being the China Center for Type Culture Collection, Wuhan University, Bayi Road, Wuchang District, Wuhan City, Hubei Province.

[0022] In the following examples, the coastal saline-alkali soil used is taken from Tangshan Park, Pinghu City, Jiaxing City, Zhejiang Province, with a pH of 7.90 and a soil electrical conductivity EC of 3.61 mS / cm.

[0023] Example 1

[0024] I. Verification of Urease Production

[0025] Inoculate the Bacillus subtilis bacterial solution (OD 600 = 1.0) onto a sterilized urea NB solid medium supplemented with phenolphthalein, and place it in a constant temperature incubator at 30°C. After culturing for 48 hours, it was found that pink colonies appeared around the colonies, indicating that the bacterium has urease activity.

[0026] The urea NB solid medium supplemented with phenolphthalein consists of: 10 g / L urea and 0.02% (w / w) phenolphthalein on an NB agar plate.

[0027] II. Carbon sequestration culture

[0028] Mix the Bacillus subtilis bacterial solution (OD 600 = 1.0) with the cementing solution to obtain a soil carbon sequestration solution. The soil carbon sequestration solution contains 0.5 mol / L urea, 0.2 mol / L calcium chloride, and 3 g / L NB nutrient broth. The addition amount of the Bacillus subtilis bacterial solution is 100 mL (10%) of the bacterial solution per 1000 g of saline-alkali soil. Add the above soil carbon sequestration solution to the coastal saline-alkali soil to be treated, add 260 g / kg of organic fertilizer, mix evenly, add ultrapure water, and adjust the soil water content to 10% - 15%. Keep the coastal saline-alkali soil to be treated in an aerobic environment, carry out constant temperature carbon sequestration culture at 25°C, stir once every 3 days during the period, and add water by the gravimetric method to maintain the soil moisture content.

[0029] III. Sample collection, separation and determination of carbon content

[0030] Collect samples of carbon sequestration culture for 10 days, 45 days and 90 days respectively.

[0031] Adjust the sieved and air-dried soil sample to a water holding capacity (WHC) of 10%, and pre-culture it at 25°C for 14 days to activate microorganisms and stabilize the mineralization rate. Subsequently, put 100 g of the sample soil into a 150 mL anaerobic bottle, and cover the bottle with tin foil with small holes. Measure the CO2 level by using a gas chromatograph (CA; Agilent 7890a) equipped with a flame ionization detector (FID). The soil CO2 emission rate R (mg Ckg -1 soil h -1 ) is calculated using the following equation:

[0032]

[0033] where C t is the concentration of CO2 in the bottle at a specific sampling time (ppm), C0 is the initial concentration of ambient CO2 before gas sampling (ppm); V is the volume of the culture bottle (m 3 ); T is the standard temperature (273.15 K); M is the molecular weight of C (12 g / mol); m is the dry weight of the soil sample (kg); Tr is the temperature at gas sampling (298.15 K); t is the duration of gas sampling (3 hours), and 22.4 (L / mol) is the molar volume of gas at 1 atm and 273.15 K.

[0034] The cumulative emissions of CO2 are calculated using the following formula:

[0035]

[0036] where C m represents the cumulative emissions of CO2 (mg C kg -1 soil); i is the number of sampling times, and R i +R i-1 is the sum of the soil CO2 emission rates R for two adjacent samplings; t i -t i-1 is the time interval (h) between two adjacent samplings.

[0037] The wet-sieving method was used to separate soil aggregates of different particle sizes in each group of samples: 100 g of soil samples passing through 2 mm were placed on the top layer of a set of sieves composed of 0.25 mm and 0.053 mm aperture sieves. After soaking with distilled water for 5 min at room temperature, it was oscillated for 2 min at a speed of 30 times / min and an up-and-down amplitude of 3 cm. The aggregates were dried and weighed, and the mean weight diameter (MWD) was used to characterize the aggregate stability.

[0038]

[0039] In the formula, w i represents the percentage of the dry weight of soil aggregates in the total dry weight within this size range, n represents the number of sieves, and x i represents the average diameter of the aggregates collected on each size sieve.

[0040] Separation and content determination of soil organic matter components: 5 g of soil samples passing through 2 mm were placed in a 50 mL centrifuge tube, and 25 mL of a solution with a density of 1.85 g / cm 3Sodium iodide (NaI) solution was added to make the sample fully mixed with the solution. Under the conditions of 25 °C and 170 rpm, the suspension was shaken for 30 min using a shaker. After standing for 20 min, the suspension was centrifuged at 3000 r / min for 30 min. Immediately after centrifugation, it was filtered by suction through a microporous membrane with a pore size of 0.45 μm, and the residue on the membrane was collected. After washing with deionized water, the light fraction (LF) was obtained. Then, 15 mL of sodium hexametaphosphate (HMP) solution with a concentration of 5 g / L was added, and it was shaken in the shaker for 18 h. After the sample was completely dispersed, it was passed through sieves with apertures of 0.25 and 0.053 mm respectively to obtain coarse particulate organic matter + sand (cPOM + sand: > 0.25 mm), fine particulate organic matter + sand (fPOM + sand: 0.053 - 0.25 mm), and mineral-associated organic matter (MAOM: < 0.053 mm). Each component was dried at 60 °C, weighed, ground to < 0.149 mm, and the soil organic carbon concentration of each component was measured by the potassium dichromate oxidation - spectrophotometer method. The organic carbon content of the light fraction (LF), the content of coarse particulate organic carbon (cPOC), the content of fine particulate organic carbon (fPOC), the content of mineral-associated organic carbon (MAOC), and the content of dissolved organic carbon (DOC) were obtained respectively. The measured results are shown in Table 1.

[0041] Table 1 Comparison of sample results of Example 1 on different days

[0042]

[0043] Comparative Example 1

[0044] Compared with Example 1, in this comparative example, only a cementing solution including 0.5 mol / L urea, 0.2 mol / L calcium chloride, and 3 g / L NB nutrient broth was added to the coastal saline-alkali soil to be treated. After mixing evenly, ultrapure water was added to adjust the soil water content to 10 - 15%. The coastal saline-alkali soil to be treated was kept in an aerobic environment and subjected to constant-temperature carbon sequestration culture at 25 °C. During this period, it was stirred once every 3 days, and water was added by the gravimetric method to maintain the soil water content. Samples of carbon sequestration culture for 10 days, 45 days, and 90 days were collected respectively. The processes of sample collection, separation, and carbon content determination were the same as those in Example 1. The measured results are shown in Table 2.

[0045] Table 2 Comparison of sample results of Comparative Example 1 on different days

[0046]

[0047] Comparative Example 2

[0048] Compared with Example 1, this comparative example only adds 260g / kg of organic fertilizer to the coastal saline-alkali soil to be treated. After mixing evenly, add ultrapure water to adjust the soil moisture content to 10-15%. Keep the coastal saline-alkali soil to be treated in an aerobic environment, and carry out constant temperature carbon fixation culture at 25°C. Stir once every 3 days during the period, and add water by weight method to maintain the soil moisture content. Collect samples of carbon fixation culture for 10 days, 45 days and 90 days respectively. The process of sample collection, separation and determination of carbon content is the same as that of Example 1. The measured results are shown in Table 3.

[0049] Table 3 Comparison of sample results on different days in comparative example 2

[0050]

[0051]

[0052] The above examples were statistically analyzed for the changes in the content of CO2 and organic carbon of each component from 10, 45, and 90 days. The results of adding organic fertilizer, binder and bacterial solution together in Example 1 reduced the emission of CO2 compared with that in Comparative Example 1 and Comparative Example 2, and the amount of CO2 emission reduced increased with the increase of days. In each group of samples treated with carbon fixation for 90 days, the results of Example 1 treated with organic fertilizer, binder and bacterial solution together reduced the emission of CO2 by 2.7244 μg C kg compared with the results of Comparative Example 1. -1 The soil CO2 emission was reduced by 6.0181 μg C kg compared with the treatment result of comparative example 2. -1 SoilCO2 emissions. For the changes in organic carbon content of each component such as aggregates, the results of adding organic fertilizer, binder and bacterial solution together in Example 1 increased the organic carbon content compared with Comparative Examples 1 and 2, among which the increase was most obvious in aggregates >0.25 mm. In each group of samples treated with carbon fixation for 45 days, compared with Comparative Examples 1 and 2, the results of Example 1 in which organic fertilizer, binder and bacterial solution were added together showed that the average organic carbon value of aggregates >0.25 mm increased by 6.46 g / kg and 5.61 g / kg, respectively, and the MAOC content increased by 4.3793 g / kg and 3.2738 g / kg. It shows that binder and bacterial solution promote the formation of large aggregates and promote carbon physical protection. The combined use of bacterial solution (microbial metabolism) and binder not only reduces carbon loss (CO2 emission), but also increases carbon fixation through the dual mechanisms of aggregate formation and mineral binding.

[0053] Example 2

[0054] In this example, the pH and soil electrical conductivity EC of soil samples during the experiments of Example 1, Comparative Example 1 and Comparative Example 2 were measured. After taking the soil samples, water was added according to the ratio of soil (air-dried) to water of 1:5, and after mixing evenly, it was allowed to stand. A pH meter (FE28, Five Easy Plus) and a conductivity meter (DDS-307, Leici) were used to measure pH and EC respectively.

[0055] Over time, the pH value of the treatment with the combined addition of organic fertilizer, cementing liquid and bacterial liquid in Example 1 decreased from the initial 8.83 to 7.93 on the 90th day, with a decrease of 10.19%. However, the pH values of the soil under the other two groups of treatments did not change significantly and basically remained at the initial level. This indicates that by using the method provided by the present invention, calcium carbonate precipitates generated by microbial metabolism neutralize alkaline ions (such as OH - ), and at the same time calcium ions (Ca 2+ ) displace sodium ions (Na + ), reducing the alkalization effect of sodium and synergistically regulating the acid-base balance of coastal saline-alkali soil.

[0056] Over time, the soil EC of the treatment with the combined addition of organic fertilizer, cementing liquid and bacterial liquid in Example 1 decreased from 3.21 mS·cm on the first day -1 to 2.79 mS·cm -1 , with a decrease of 13.08%. The reduction value of EC in the group with only organic fertilizer added in Comparative Example 2 was less than that of the soil in Example 1 with the combined addition of organic fertilizer, cementing liquid and bacterial liquid. It shows that the addition of organic fertilizer can reduce the EC of coastal saline-alkali soil to a certain extent, but its effect is limited. The addition of Bacillus subtilis can further reduce the ion concentration in the soil solution, and the two have a synergistic effect.

[0057] Example 3

[0058] In this example, the microbial community structure analysis of the soil samples after the experiments of Example 1, Comparative Example 1 and Comparative Example 2 was carried out.

[0059] In Example 1, the treatment with the combined addition of organic fertilizer, cementing liquid and bacterial liquid through the physical wrapping effect of calcium carbonate precipitation and Ca 2+The chemical complexation effect reduces the contact between organic carbon and decomposing microorganisms, effectively reducing the cumulative CO2 release (26.12% and 43.85% less than Comparative Example 1 and Comparative Example 2, respectively). At the same time, Bacillus subtilis promotes the formation of mineral-organic complexes, inhibits the gene expression of cellulolytic enzymes (such as GH74 and GH94), and slows down the mineralization process of organic carbon, thereby enhancing the long-term stability of organic carbon. High-throughput sequencing and metagenomic analysis show that the addition of organic fertilizer, cementing liquid, and bacterial liquid in Example 1 can enrich chemolithoautotrophic bacteria (such as Sulfurivermis and Muriiphilus). The metabolic advantage of the autotrophic bacterial community indirectly enhances the accumulation of organic carbon by reducing the competitive consumption of easily decomposable carbon.

[0060] In addition, the addition of organic fertilizer, cementing liquid, and bacterial liquid in Example 1 activates the genes related to the Calvin cycle, and their relative abundances increase by 39.37% and 29.11% compared with Comparative Example 1 and Comparative Example 2, respectively, indicating that the enhancement of autotrophic carbon fixation ability is an important driving force for the improvement of carbon fixation efficiency.

[0061] In Example 1, urease-producing functional bacteria (Bacillus subtilis) and a cementing liquid were added. Bacillus subtilis can decompose urea in the cementing liquid to produce ammonia and carbon dioxide; carbon dioxide is converted into carbonate ions in an alkaline environment; Bacillus subtilis absorbs calcium ions onto their cell surfaces. When calcium ions meet carbonate ions, a large amount of calcium carbonate crystals will form and deposit on the bacterial surface. This process is called MICP. According to the results, after MICP treatment in Example 1, carbon degradation pathways such as glycolysis and the citric acid cycle are inhibited, reducing the oxidative decomposition of organic carbon. Therefore, MICP treatment can reduce organic carbon mineralization and improve carbon sequestration efficiency.

[0062] In summary, the present invention mainly uses a Bacillus subtilis and a cementing liquid to promote carbon sequestration in coastal saline-alkali soils. In this method, urease-producing functional bacteria decompose and activate urea and calcium sources in the cementing liquid, absorb CO2 to form calcium carbonate, cement saline-alkali soil particles and organic carbon to form soil aggregates, and improve the direct carbon sequestration performance of the soil; at the same time, the formation of soil aggregates leads to the evolution of the physical and chemical properties and dominant functional bacterial communities of coastal saline-alkali soils, enriches autotrophic carbon-fixing microorganisms, and further improves the indirect carbon sequestration performance of the soil. The method provided by the present invention has a positive effect on both soil treatment and improvement and the carbon neutrality goal.

[0063] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical fields can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for rapidly improving the carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation through MICP, characterized in that: The urease-producing functional bacteria liquid and the cementing liquid are mixed to be used as soil carbon fixation liquid; the soil carbon fixation liquid is added to the coastal saline-alkali soil to be treated, and organic fertilizer is added and mixed to keep the coastal saline-alkali soil to be treated in an aerobic environment; the urease-producing functional bacteria decompose and activate the urea and calcium source in the cementing liquid, absorb CO2 to form calcium carbonate to cement the saline-alkali soil particles and organic carbon to form soil aggregates, thereby improving the direct carbon fixation performance of the soil, and improving the indirect carbon fixation performance of the soil by in-situ enrichment of autotrophic carbon fixation microorganisms.

2. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 1, characterized in that: The functional bacteria producing urease activity is Bacillus subtilis; the Bacillus subtilis is preserved in the China Center for Type Culture Collection with a preservation number of CCTCC·WB·2008694 and a preservation date of November 15, 2006. The address of the preservation unit is China Center for Type Culture Collection of Wuhan University, Bayi Road, Wuchang District, Wuhan City, Hubei Province.

3. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: The cementing liquid includes urea, calcium chloride and NB nutrient broth; the urea content in the soil carbon fixation liquid is 0.4-0.6 mol / L, the calcium chloride content is 0.15-0.3 mol / L calcium chloride, and the NB nutrient broth content is 2-4 g / L.

4. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: The OD of the urease-producing functional bacterial solution is 600 It is 0.8~1.

2.

5. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: The amount of the urease-producing functional bacteria solution added to the soil carbon fixation solution is 80 to 120 mL of the bacteria solution per 1000 g of saline-alkali soil.

6. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: The amount of organic fertilizer added to the coastal saline-alkali soil to be treated is 240-260 g / kg.

7. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: The application amount of the soil carbon fixation liquid is 1 to 3 L per square meter of soil.

8. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: The coastal saline-alkali soil to be treated is plowed by a rotary tiller, and the soil carbon fixation liquid is sprayed while plowing; the number of plowing and spraying the soil carbon fixation liquid is 2 to 3 times.

9. The method for rapidly improving carbon fixation performance of coastal saline-alkali land by promoting soil aggregate formation by MICP according to claim 2, characterized in that: During the process of improving the carbon fixation performance of the coastal saline-alkali soil to be treated, the temperature is controlled at 24-26° C., the soil moisture content is 10%-15%, and the carbon fixation period is 10-90 days.

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