Acid polluted soil carbon emission reduction method based on coupled ecological system

Abstract

The invention discloses an acid contaminated soil carbon emission reduction method based on a coupled ecological system, which comprises the following steps: adding rice straw biochar into acid contaminated soil, planting plants which are perennial ryegrass, and after the plants are cultivated to a mature period, strengthening the photosynthesis capability of the plants and the carbon sequestration capability of the soil at the same time, so as to improve the carbon sequestration capability of the acid contaminated soil. The negative increase of the CO2 emission cumulant and the remediation of the acidic polluted soil are realized. According to the method, the emission cumulant of CO2 in the acid polluted soil is greatly reduced, the total absorption amount of CO2 reaches up to 193.41 g / m < 2 >-304.41 g / m < 2 >, and the method has the advantages that raw materials are low in cost and easy to obtain, operation is easy, the operation cost is low, secondary pollution is avoided, and the method is suitable for large-scale use and has wide application prospects in the field of carbon emission reduction of the acid polluted soil (such as heavy metal pollution).

Description

Technical Field

[0001] The present invention belongs to the technical field of soil carbon emission reduction, and particularly relates to a method for reducing carbon emissions from acidic polluted soil based on a coupled ecological system. Background Art

[0002] With the acceleration of the industrialization process, acid rain has become one of the main environmental problems faced by people's lives. Long-term leaching of acid rain will lead to soil acidification, nutrient loss, instability of soil aggregate structure, inhibition of normal growth activities of plants and microorganisms, and at the same time change the state of soil organic carbon, affecting the global carbon cycle, resulting in an increase in the concentration of CO 2 in the atmosphere. In addition, due to the increase in human activities, heavy metals are retained in the soil for a long time and widely. Soil acidification and heavy metal pollution often occur simultaneously. Heavy metal pollution affects the physical and chemical properties of the soil, inhibits plant productivity, soil enzyme activity and the normal metabolic activities of soil microorganisms, and then affects the transformation and accumulation of soil organic carbon, ultimately causing serious damage to the soil carbon pool. Therefore, the reduction of heavy metal acidic polluted soil is particularly important, which will be beneficial to environmental protection and public health and alleviate climate warming.

[0003] The strength of plant photosynthesis and soil carbon sequestration ability are the most important key factors determining carbon emission reduction. In the prior art, inorganic / organic materials are usually used in a chemical way to neutralize soil acidity and increase the organic matter in the soil system to achieve carbon sequestration in acidic soil, or specific plants are planted to absorb CO 2 in the atmosphere. Biochar refers to a class of highly aromatic porous carbonaceous materials generated by the thermochemical reaction of waste biomass under anaerobic or anoxic conditions. Biochar can exist in the soil environment for a long time compared with the original biomass, and delay the emission of soil greenhouse gases by improving the soil structure and microbial community. However, when biochar is applied alone for soil carbon emission reduction, biochar cannot absorb CO 2 , and the carbon sequestration and emission reduction effect is very limited. Moreover, when the application level is too high, it is easy to cause secondary pollution. When specific plants are planted alone for soil carbon emission reduction, the low pH value of the soil and the presence of pollutants will seriously affect the nutrient absorption, photosynthesis efficiency and growth and development activities of plants, and the sustainability is not strong. Therefore, how to overcome the above problems and obtain a method for reducing carbon emissions from acidic polluted soil based on a coupled ecological system, so as to simultaneously enhance plant photosynthesis and soil carbon sequestration ability, is of great significance for achieving stable, sustainable and efficient carbon reduction goals for acidic polluted soil. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for reducing carbon emissions from acidic polluted soil based on a coupled ecological system.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A method for carbon emission reduction in acidic polluted soil based on a coupled ecological system, comprising the following steps: adding rice straw biochar to acidic polluted soil, planting plants, and when the plants are cultivated to the mature stage, realizing negative growth of the cumulative CO 2 emission and the remediation of acidic polluted soil by simultaneously strengthening the photosynthesis ability of the plants and the carbon sequestration ability of the soil; the plant is perennial ryegrass.

[0007] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the mass ratio of the rice straw biochar to the acidic polluted soil is 0.001-0.01:1.

[0008] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the mass ratio of the rice straw biochar to the acidic polluted soil is 0.005-0.01:1.

[0009] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the rice straw biochar is prepared by the following method: pyrolyzing rice straw under oxygen-limited conditions to obtain rice straw biochar; the temperature of the pyrolysis is 450°C-500°C, the time of the pyrolysis is 2h-3h, and the heating rate during the pyrolysis process is 5°C / min-10°C / min.

[0010] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the following treatment is also included before using the rice straw: harvesting at the stage when the rice is mature but not completely dry to ensure its nutritional value and structural integrity, removing the leaves and leaf sheaths, washing the rice straw, drying it to a moisture content of 10%-15%, pulverizing it, and sieving it; the temperature of the drying is 70°C, and the sieving is through a 100-mesh sieve.

[0011] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the pH value of the acidic polluted soil is 4-5, the acidic polluted soil contains heavy metals, the concentration of heavy metals in the acidic polluted soil is 5mg / kg-10mg / kg, and the heavy metals include cadmium.

[0012] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the perennial ryegrass is planted with ryegrass seeds, and the seeding rate of the ryegrass seeds is 2g-3g of ryegrass seeds per kilogram of acidic polluted soil.

[0013] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, before using the ryegrass seeds, the following treatments are further included: screening, disinfecting, and soaking the ryegrass seeds; the specific process of the screening is: selecting ryegrass seeds with similar sizes and plump grains, placing them in a sodium chloride solution, screening, and removing the floating seeds and impurities; the mass fraction of the sodium chloride solution is 10%; the specific process of the disinfection is: soaking the screened ryegrass seeds in an aqueous hydrogen peroxide solution for 15 minutes, washing, and drying; the soaking is carried out under stirring conditions, and the mass fraction of the aqueous hydrogen peroxide solution is 3%; the specific process of the seed soaking is: first soaking the disinfected ryegrass seeds in water at 40°C to 50°C for 10 minutes to 15 minutes, and then soaking them in water at 15°C to 20°C for 12 hours.

[0014] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the cultivation time is 45 days to 60 days; during the entire cultivation stage, water is regularly applied, and the watering frequency is 1 time / day to 2 times / day, so as to keep the soil moisture reaching 60% to 70% of the maximum water holding capacity of the field; from the 0th to the 14th day of cultivation, the soil is loosened every week, and then the modified Hoagland's nutrient solution is irrigated.

[0015] After adding the rice straw biochar to the acidic polluted soil, the following treatments are further included: standing for 10 days to 15 days to ensure the homogenization between the rice straw biochar and the soil, then irrigating the nutrient solution, turning the soil to enhance the air permeability and water permeability of the soil, and starting to plant when the soil surface is dry; the nutrient solution is the diluted modified Hoagland's nutrient solution, and the preparation process of the diluted modified Hoagland's nutrient solution is: mixing the modified Hoagland's nutrient solution and water, and the volume ratio of the modified Hoagland's nutrient solution to water is 1:200.

[0016] For the above-mentioned method for carbon emission reduction in acidic polluted soil, preferably, the number of microbial species in the soil in the coupled ecological system is 788 to 870, and the bacterial community structure mainly consists of Chloroflexi, Actinobacteria, Proteobacteria, and Acidobacteria.

[0017] Compared with the prior art, the advantages of the present invention are as follows:

[0018] (1) Aiming at the problems of accelerated decomposition of organic carbon, changed soil enzyme activity, restricted plant growth, and difficulty in achieving efficient carbon emission reduction in acidic polluted soil, the present invention creatively proposes a method for carbon emission reduction in acidic polluted soil with a coupled ecological system. By constructing a coupled ecological system of rice straw biochar - acidic polluted soil - ryegrass - microorganism, the photosynthesis of plants and the carbon sequestration ability of the soil are enhanced synchronously. While the plant absorbs CO 2Meanwhile, it inhibits the mineralization process of soil organic carbon in acidic soil, thereby maximizing the emission reduction efficiency, achieving the goal of efficient, stable and sustainable carbon reduction in acidic polluted soil, and ultimately realizing negative growth of carbon emissions. Specifically, on the one hand, the method of the present invention increases the contents of chlorophyll a, chlorophyll b and carotenoids in ryegrass leaves, protects the reaction site of photosynthesis, and thus improves the activity of the light reaction of photosynthesis; promotes the consumption of the end photosynthetic products (sucrose and starch) of the Calvin cycle in leaves, and thus improves the efficiency of the Calvin cycle of photosynthesis; and at the same time alleviates the oxidative stress of plants under acidic pollution, and finally promotes plants to absorb CO 2 in the atmosphere; on the other hand, the method of the present invention regulates the activities of soil carbon cycle-related enzymes (soil invertase and soil β-glucosidase); reduces the overall carbon metabolism ability of the soil microbial community; and changes the microbial community structure and the composition of dominant bacterial groups in the soil, so that the abundance of specific bacterial species (such as norank_f__JG30-KF-AS9) that can inhibit soil carbon mineralization is greatly increased; and regulates the ecological functions of the soil environment, down-regulates the expression of the biological function of cellulose decomposition in the soil while up-regulating the expression of the fermentation function and the ecological function of oxygen-producing photosynthetic microorganisms, and finally enhances the carbon sequestration ability of the soil and realizes the negative growth of CO 2 . The method of the present invention greatly reduces the cumulative emission amount of CO 2 in acidic polluted soil, and its total absorption amount of CO 2 is as high as 193.41 g / m 2 ~304.41 g / m 2 . It has the advantages of low-cost and easily available raw materials, simple operation, low operating cost, no secondary pollution and being suitable for large-scale use, etc., and has broad application prospects in the field of carbon emission reduction in acidic polluted soil (such as heavy metal pollution).

[0019] (2) The rice straw biochar prepared by pyrolysis under the preferred medium-temperature and low-oxygen conditions in the present invention has a higher surface area, porosity, and carbon content, as well as a lower mineralization rate, which is more conducive to the colonization of rhizosphere soil microorganisms, the growth and development of plants, and soil carbon sequestration. Specifically, on the one hand, as a silicon-rich plant, the biochar obtained by pyrolyzing rice straw has a richer silicon content compared to other straw biochars. The silicon-hemicellulose matrix formed during the pyrolysis of this biochar can complex and precipitate with Cd. The released silicon can be deposited in the endodermis and epidermal cell walls of plants and downregulate the genes involved in Cd accumulation, thereby reducing the toxicity of Cd to plants. Therefore, it has stronger pollution remediation ability. In addition, the formation of a dense silicon-encapsulated carbon structure due to the pyrolysis of carbon and silicon at medium temperatures can protect the aromatic carbon components in the biochar from physical and chemical oxidation, thereby generating a greater carbon sequestration potential. On the other hand, the mineral nutrients contained in the rice straw biochar can increase the content of essential nutrient elements for plants, improve the water and fertilizer retention capacity and porosity of the soil, reduce soil nutrient loss, and enhance the stress resistance of plants, thus promoting the growth and development of plants.

[0020] (3) The preferred perennial ryegrass in the present invention has the advantages of low price, well-developed roots, rapid growth, the ability to adapt to various soil types, strong regeneration ability, and heavy metal absorption and accumulation ability. Under acidic pollution conditions, perennial ryegrass has the best photosynthetic productivity and also has a certain soil remediation ability. The method of the present invention can further improve the plant growth and development performance, promote the carbon sink function, improve the resource utilization efficiency, and extend the utilization cycle by finely cultivating perennial ryegrass seeds, including means such as seed selection, disinfection, seed soaking, soil loosening, and nutrient solution flooding, as well as mixing and applying rice straw biochar.

[0021] (4) The method of the present invention, by optimizing the mass ratio of rice straw biochar to acidic polluted soil to be 0.001 - 0.01∶1, regulates the plant physiological function indexes, soil physical and chemical properties, and soil microbial carbon metabolism ability in the system, which is more conducive to reducing the emission of CO 2 from acidic polluted soil and reducing the total amount and toxicity of pollutants. Description of the Drawings

[0022] Figure 1 SEM image of the rice straw biochar (RB) in Example 1 of the present invention.

[0023] Figure 2 Element distribution map of the rice straw biochar (RB) in Example 1 of the present invention.

[0024] Figure 3 FI-TR diagram of the rice straw biochar (RB) in Example 1 of the present invention.

[0025] Figure 4It is the ultra - microstructural diagram of ryegrass chloroplasts and thylakoids under different treatment methods in Example 1 of the present invention.

[0026] Figure 5 It is the content diagram of hydrogen peroxide and malondialdehyde in ryegrass leaf tissue under different treatment methods in Example 1 of the present invention.

[0027] Figure 6 It is the soil enzyme activity diagram related to the carbon cycle in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0028] Figure 7 It is the overall carbon metabolic capacity diagram of the microbial community in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0029] Figure 8 It is the LEfSe multi - level species difference discrimination diagram of the microbial community structure in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0030] Figure 9 It is the ecological function prediction diagram related to the carbon cycle in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0031] Figure 10 It is the dynamic change trend diagram of the CO 2 flux rate in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0032] Figure 11 It is the total emission diagram of CO 2 in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0033] Figure 12 It is the content change diagram of bio - available Cd in acidic contaminated soil under different treatment methods in Example 1 of the present invention.

[0034] Figure 13 It is the flow chart of the coupled ecological system constructed in the present invention. Specific Embodiments

[0035] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0036] Example 1:

[0037] An acidic contaminated soil carbon emission reduction method based on a coupled ecological system of the present invention includes the following steps:

[0038] S1. Soil pretreatment and poisoning treatment

[0039] The random sampling method was used to sample and measure the pH value of the sampled soil in the field. Moderately acidic soil with a pH value of 4 - 5 was collected, air-dried in a cool and well-ventilated place indoors, and after removing plant residues, it was ground and passed through a 10-mesh sieve (2.0 mm) to obtain the treated acidic soil. Then, the Cd(NO 3 ) 2 solution was slowly added to the treated acidic soil (soil:water = 3:1), and it was placed in a dark room to equilibrate for 60 days. During this period, the soil was stirred at a frequency of 2 - 3 days / time to ensure the homogenization of the soil and the pollutant cadmium. After the equilibration period expired, the treated soil was taken out, air-dried, ground, and passed through a 10-mesh sieve to obtain cadmium-containing acidic polluted soil, which was stored in an opaque sealed glass jar for standby. After testing, the total cadmium concentration in the cadmium-containing acidic polluted soil was 8.10 mg / kg, and its pH value was 4.46.

[0040] S2. Preparation of carbon-based materials

[0041] The period when the rice was mature but not completely dry was selected for harvesting to ensure its nutritional value and structural integrity. After removing the leaves and leaf sheaths, the obtained rice straw was washed, placed in a 70°C vacuum drying oven and dried until the moisture content was 10% - 15%, then crushed and passed through a 100-mesh sieve (0.15 mm) to obtain straw powder, which was stored in a sealed container for standby. After weighing the straw powder, it was placed in a crucible, and the mouth of the crucible was tightly covered with tin foil to ensure good sealing. After covering, under an oxygen-limited condition, it was pyrolyzed in a muffle furnace at a heating rate of 5°C / min to 450°C for 2 h, cooled to room temperature, quickly ground and passed through a 100-mesh sieve to obtain rice straw biochar, denoted as RB, which was stored in an opaque sealed glass jar for standby. Among them, the yield of rice straw biochar was 42.43%.

[0042] S3. Soil cultivation

[0043] Mix the cadmium - contaminated acidic soil obtained in step S1 with the rice straw biochar obtained in step S2 according to the mass ratios of rice straw biochar to cadmium - contaminated acidic soil of 0.001:1, 0.005:1, and 0.01:1 respectively, that is, stir with a mechanical stirrer in a solid - solid mixing manner for 1 h, and let it stand in a dark environment for 10 days to ensure homogenization between the materials and the soil; then, slowly add deionized water to saturate the soil moisture, gently stir the soil slowly until the moisture is uniform, and then let it stand in a dark environment for 48 h. After that, flood the diluted modified Hoagland's nutrient solution into the soil to ensure that the nutrient solution is evenly distributed in the soil, and turn the soil again to enhance the air permeability and water permeability of the soil. Wait until the soil surface is dry. Among them, mix the modified Hoagland's nutrient solution and water according to the volume ratio of the modified Hoagland's nutrient solution to water of 1:200 to obtain the diluted modified Hoagland's nutrient solution. Among them, when the mass ratio of rice straw biochar to cadmium - contaminated acidic soil is 0.001:1, it is denoted as the RB - 1 group; when the mass ratio of rice straw biochar to cadmium - contaminated acidic soil is 0.005:1, it is denoted as the RB - 2 group; when the mass ratio of rice straw biochar to cadmium - contaminated acidic soil is 0.01:1, it is denoted as the RB - 3 group.

[0044] S4. Plant selection and planting

[0045] S4 - 1. Select ryegrass seeds with similar sizes and plump grains, place them in a NaCl solution with a mass percentage of 10%, and sieve out the floating seeds and sundries; place the screened ryegrass seeds in a hydrogen peroxide aqueous solution (H 2 O 2 solution) with a mass percentage of 3% and soak for 15 min. Stir every 5 min during the soaking period to ensure that all seeds can contact the H 2 O 2 solution. After the soaking is over, thoroughly rinse the seeds with deionized water 3 times, and place them in a dark, cool and ventilated place to dry naturally to obtain disinfected ryegrass seeds; place the disinfected ryegrass seeds in warm water at 40 °C - 50 °C for 10 min - 15 min, and then transfer them to deionized water at 15 °C - 20 °C and soak for 12 h. Use a sieve to sieve out the seeds and drain the excess water to obtain treated ryegrass seeds.

[0046] S4-2. Directly sow the treated ryegrass seeds obtained in step S4-1 into the mixed soil (RB-1 group, RB-2 group, RB-3 group) in step S3. The seeding rate of ryegrass seeds is 3 g of seeds / kg of dry soil (this dry soil refers to the cadmium-containing acidic contaminated soil in step S1). The seeds do not adhere to each other. After covering the seeds with a soil layer of 1 cm to 2 cm in thickness, water until the soil surface is moist, and grow and cultivate for 60 days to achieve the remediation of cadmium-containing acidic contaminated soil. In the early growth stage, that is, from the 0th to the 14th day after sowing, loosen the soil and irrigate with Holland's nutrient solution once every week. Specifically: first, water an appropriate amount to moisten the soil, loosen the surrounding soil in a rotating manner, and pour the diluted Holland's nutrient solution after loosening the soil, and ensure uniform coverage of the root area of the plants; during the entire growth period, water regularly at a frequency of once every 2 days to ensure that the soil moisture reaches 60% of the field capacity.

[0047] S5. Determination of plant photosynthesis and soil carbon sequestration capacity

[0048] Use a biological transmission electron microscope (TEM) to observe the ultrastructure of leaf chloroplasts and thylakoids; measure the contents of chlorophyll a, chlorophyll b, and carotenoids in plants to analyze the activity of the light reaction of photosynthesis; measure the contents of sucrose, starch, and soluble proteins to analyze the activity of the dark reaction of photosynthesis; measure the content of reactive oxygen species and the activity of antioxidant enzymes to analyze the impact of oxidative damage on photosynthesis; measure the activities of soil sucrase and β-glucosidase to analyze the activities of soil carbon cycle-related enzymes; use a Biolog-ECO microplate to analyze the overall soil carbon metabolism status; use 16S rRNA high-throughput sequencing technology to analyze the structural differences of soil microbial communities, and use the FAPROTAX ecological function prediction technology to analyze the soil microbial-related carbon metabolism ecological functions.

[0049] Control group 1 (CK): Do not apply rice straw biochar (RB), and other conditions are the same.

[0050] Control group 2 (WB): Use corn straw biochar to replace rice straw biochar, and the mass ratio of corn straw biochar to cadmium-containing acidic contaminated soil is 0.01:1, and other conditions are the same.

[0051] Control group 3 (OP): Use Solanum nigrum to replace ryegrass, that is, plant Solanum nigrum seeds, and other conditions are the same.

[0052] Control group 4 (OCK): Do not apply any biochar, and use Solanum nigrum to replace ryegrass, and other conditions are the same.

[0053] Among them, the corn straw biochar used in the second control group is prepared by the following steps: Weigh the corn straw powder and place it in a crucible, pyrolyze it at 450 °C for 2 h in a muffle furnace under oxygen-limited conditions, and the heating rate during pyrolysis is 5 °C / min to obtain corn straw biochar, denoted as WB.

[0054] (I) Characterization of rice straw biochar

[0055] The surface morphology and element distribution of the obtained materials were characterized by scanning electron microscopy combined with energy dispersive spectrometer (SEM-EDS), and the surface functional groups of the materials were characterized by Fourier transform infrared spectrometer (FT-IR).

[0056] Figure 1 This is the SEM image of the rice straw biochar (RB) in Example 1 of the present invention. Figure 2 This is the element distribution map of the rice straw biochar (RB) in Example 1 of the present invention. Figure 3 This is the FT-IR image of the rice straw biochar (RB) in Example 1 of the present invention. From Figure 1 It can be seen that the pore structure of RB is relatively dense and regular, and there is a small amount of flocculent substances attached to the surface. From Figure 2 It can be seen that the main constituent elements of RB not only include C, O, N, S, Si, but also include trace metal elements essential for life such as Ca, K, Mg, Na, Fe, etc. From Figure 3 It can be seen that the presence of a large number of substituted aromatic hydrocarbons in RB is the source of the high stability of RB and ensures the strong carbon sequestration ability of RB; at the same time, 2829 - 2990 cm -1 is the absorption band of saturated alkanes, indicating the presence of aliphatic carbon compounds in RB, which is of great significance for the growth and development of plants and microorganisms; in addition, the extensive presence of -OH, -CHO and -COOH is observed on the surface of RB, which can not only serve as the binding sites of heavy metal ions to selectively adsorb Cd to reduce its migration and toxicity, but also enhance the soil carbon sequestration efficiency by promoting the formation of mineral-bound organic carbon, isolating pollutants, affecting plant growth and development, and inhibiting the activity of specific microbial populations.

[0057] (II) Changes in the photosynthetic capacity of ryegrass

[0058] When ryegrass grows to 60 days old, fresh leaf tissues are taken and the ultrastructures of leaf chloroplasts and thylakoids are observed with a biological transmission electron microscope (TEM), as shown in Figure 4 shown. The contents of chlorophyll a, chlorophyll b and carotenoids in plants are measured to analyze the activity of the light reaction of photosynthesis, as shown in Table 1. The contents of sucrose, starch and soluble proteins are measured to analyze the activity of the dark reaction of photosynthesis, as shown in Table 2. The contents of reactive oxygen species and the activities of antioxidant enzymes are measured to analyze the influence of oxidative damage on photosynthesis, as shown in Figure 5 shown.

[0059] Table 1 Data of photosynthetic pigment content in ryegrass leaves under different treatment methods

[0060]

[0061] Table 2 Data of photosynthetic product content in ryegrass leaves under different treatment methods

[0062]

[0063] Photosynthetic pigments play a key role in light energy absorption, generation of excited-state electrons, transfer stability of the electron transport chain, photoprotection, and photoacclimation regulation. According to Table 1, compared with the CK group, the contents of chlorophyll a, chlorophyll b, carotenoid, and total chlorophyll in the leaves of ryegrass in the RB-1 group, RB-2 group, and RB-3 group were significantly increased, and the increase ranges were 12.60% - 21.68%, 47.13% - 113.33%, 1.80% - 15.84%, and 14.11% - 23.34% respectively. In addition, the WB group increased the content of photosynthetic pigments, and the effect was not much different from that of the RB-3 group.

[0064] The stability of the chloroplast and thylakoid structures determines the correct arrangement and function of photosynthetic pigments and related enzymes, thereby affecting the absorption, transfer, and conversion of light energy by the leaves. Figure 4 This is the ultrastructure diagram of chloroplasts and thylakoids of ryegrass under different treatment methods in Example 1 of the present invention. Figure 4 In, RB represents the RB-3 group. Figure 4 In, CW: cell wall, Chl: chloroplast, T: thylakoid, SG: starch grain, DG: granule disorder, RCM: chloroplast membrane rupture, Os: osmiophilic granule, G: grana, T: thylakoid, M: mitochondrion. From Figure 4 It can be seen that after applying rice straw biochar, obvious changes occurred in the chloroplast and thylakoid structures of ryegrass leaves. Specifically, the chloroplasts in the CK group shrank, the starch grains occupied a relatively large part of the chloroplast volume, the granule arrangement was disordered, some thylakoids were swollen, and the chloroplast membranes of some chloroplasts were broken; while compared with the CK group, the RB-3 group had more chloroplasts, more thylakoids, and a more regular arrangement.

[0065] CO 2Carboxylation and reduction occur in the Calvin cycle, resulting in the production of glyceraldehyde-3-phosphate. Then, glyceraldehyde is transported to the cytoplasm as a precursor and converted into sucrose or starch, which is stored in the chloroplast. Therefore, sucrose and starch, as the key end products of photosynthetic carbon fixation, play a crucial role in the efficiency of the dark reaction of photosynthesis. As can be seen from Table 2, compared with the CK group, the utilization of leaf starch and sucrose in the RB-1 group, RB-2 group, and RB-3 group increased, which may indicate an enhancement of carbon assimilation ability. In addition, compared with the CK group, there was no significant difference in the soluble protein content in the WB group, while the starch and sucrose contents decreased significantly, but the degree of this decrease was much less than that in the RB-3 group.

[0066] Pollution stress can trigger the excessive accumulation of reactive oxygen species (ROS) in plant tissues, leading to an imbalance in the redox state of the chloroplast stroma, severe lipid peroxidation of the chloroplast and thylakoid membranes, inhibition of the transport of photosynthetic electrons in the photosystem, and downregulation of the CO 2 fixation genes. Figure 5 This is a graph showing the contents of hydrogen peroxide and malondialdehyde in the leaf tissues of ryegrass under different treatment methods in Example 1 of the present invention. From Figure 5 it can be seen that compared with the CK group, after applying rice straw biochar, the content of hydrogen peroxide (H 2 O 2 ) in the leaves of ryegrass in the RB-1 group, RB-2 group, and RB-3 group decreased by 22.33% - 122.37%, and the content of malondialdehyde (MDA) decreased by 31.35% - 96.08%. The contents of both decreased significantly, indicating a reduction in the accumulation of reactive oxygen species and alleviation of oxidative damage in ryegrass. In addition, compared with the CK group, the WB group could significantly alleviate the oxidative stress of ryegrass.

[0067] The above results comprehensively show that by increasing the content of photosynthetic pigments, protecting the structure of the photosynthetic site, reducing the accumulation of photosynthetic end products, and alleviating cellular oxidative damage, after applying rice straw biochar, the photosynthetic ability of ryegrass in the RB-1 group, RB-2 group, and RB-3 group was improved either directly or indirectly; at the same time, the dry weight of ryegrass increased significantly by 44.84% - 197.37%, which also reflected the enhancement of the photosynthetic ability of ryegrass. In addition, applying corn straw biochar (WB group), although it increased the content of plant photosynthetic pigments, promoted the consumption of photosynthetic end products, and alleviated oxidative damage, and could enhance the photosynthesis efficiency to a certain extent, its promotion effect on the Calvin cycle was significantly inferior to that of the RB-3 group.

[0068] (III) Changes in the carbon sequestration ability of acidic polluted soil

[0069] The activities of soil sucrase and β-glucosidase were measured to analyze the activities of soil carbon cycle-related enzymes, as shown in Figure 6 the figure. The overall carbon metabolism status of the soil was analyzed using a Biolog-ECO microplate, as shown inFigure 7 As shown, the 16S rRNA high-throughput sequencing technology was used to analyze the richness, diversity and structural differences of soil microbial communities, and the FAPROTAX ecological function prediction technology was used to analyze the ecological functions related to carbon metabolism of soil microorganisms, as shown in Figure 8 and Figure 9 shown.

[0070] Soil sucrase can enzymatically hydrolyze sucrose into glucose and fructose in the soil and is also considered a reflection of the soil nutrient value. Soil β-glucosidase is an important part of the cellulase hydrolysis enzyme system. It can hydrolyze the glycosidic bond between aryl or hydroxyl and sugar to form glucose and is one of the indicators for evaluating the organic carbon mineralization ability in the soil. Figure 6 This is the soil enzyme activity diagram related to the carbon cycle in acidic polluted soil under different treatment methods in Example 1 of the present invention. From Figure 6 it can be seen that compared with the CK group, after applying rice straw biochar, the activity of soil β-glucosidase showed a gradually decreasing trend (35.46% - 60.05%), while the activity of soil sucrase showed a gradually increasing trend (24.07% - 64.35%). This indicates that the addition of rice straw biochar can stimulate the decomposition of active carbon, providing nutrients for microorganisms and plants, but hinders the conversion of the recalcitrant carbon pool to active carbon. In addition, compared with the CK group, the activities of soil sucrase and β-glucosidase in the WB group were significantly increased.

[0071] The organic carbon metabolic ability is one of the key factors regulating soil carbon emissions. A relatively high organic carbon metabolic ability means that soil microorganisms can decompose organic carbon compounds into CO 2 more quickly, thus increasing the soil carbon mineralization rate. Figure 7 This is the overall carbon metabolic ability diagram of the microbial community in acidic polluted soil under different treatment methods in Example 1 of the present invention. From Figure 7 it can be seen that compared with the CK group, after applying rice straw biochar, the average well color development rate (AWCD) of each well in the RB-1 group, RB-2 group, and RB-3 group of microplates decreased significantly by 59.91% - 91.37% (p < 0.05). This means that rice straw biochar significantly inhibited the overall ability of the microbial community in the rhizosphere soil of ryegrass to metabolize and mineralize carbon source substrates. In addition, compared with the CK group, the AWCD value in the WB group increased significantly, indicating that corn straw biochar would strengthen the overall metabolism and mineralization ability of soil organic carbon, which would instead increase the emission of soil CO 2 emissions.

[0072] Figure 8 This is the LEfSe multi-level species difference discrimination diagram of the microbial community structure in acidic polluted soil under different treatment methods in Example 1 of the present invention. Figure 8 In it, RB represents the RB-3 group. Figure 8Among them, different - colored nodes represent microbial taxa that are significantly enriched in the corresponding groups and have a significant impact on the differences between groups (LDA > 3.0). After detection, after applying RB, the number of microbial species in the soil decreased from 980 to 866, indicating the impact of RB on the soil microbial community structure. From Figure 8 It can be seen that the dominant bacteria in the rhizosphere soil of the CK and RB - 3 groups both come from Chloroflexi, Acidobacteria, Proteobacteria, and Actinobacteria. It is believed that Chloroflexi can fix environmental CO through the 3 - hydroxypropionate double - cycle and Calvin - cycle pathways 2 . Actinomycetes can promote the decomposition of soil organic carbon sources such as chitin and cellulose to produce CO 2 . Acidobacteria are also considered very beneficial for the production of CO 2 because most of them carry genes encoding acetate oxidation. Proteobacteria include many nitrogen - fixing bacteria, which can effectively improve the nitrogen - fixing ability of the repaired soil. In this example, compared with the CK group without applying rice straw biochar, the relative abundances of Chloroflexi and Proteobacteria in the RB - 3 group increased by 20.31% and 16.64% respectively, while the abundances of Actinobacteria and Acidobacteria decreased by 24.88% and 16.18% respectively, indicating a decrease in the soil carbon emission potential in the RB - 3 group. Among them, the abundance of norank_f__JG30 - KF - AS9 from Chloroflexi increased significantly by 39.84% (p < 0.05). As the genus with the largest proportion, it is considered that it can reduce the soil carbon mineralization rate by inhibiting the activity of organic matter - degrading enzymes. In addition, Nocardioidaceae enriched in the RB - 3 group (LDA = 3.21, p < 0.05) has metal resistance and tolerance, enabling them to maintain high metabolic activity in heavy - metal - contaminated soil, and at the same time can produce siderophores to enhance plant nutrition and defend against plant - pathogenic fungi, as well as auxins to stimulate plant growth.

[0073] Figure 9 This is the predicted map of ecological functions related to carbon cycling in acidic contaminated soil under different treatment methods in Example 1 of the present invention. Figure 9 Among them, RB represents the RB - 3 group. Based on the predicted analysis results of bacterial ecological functions by FAPROTAX, the ecological functions related to carbon cycling are relatively prominent in soil ecological functions, and the total relative abundance has no significant change. Cellulolysis represents the process of hydrolyzing cellulose in the soil into monosaccharides, and these sugars are easily mineralized by microorganisms to form CO 2 . From Figure 9 it can be seen that compared with the CK group, after adding rice straw biochar, the relative abundance of the cellulolysis function in the RB - 3 group decreased significantly by 30.35% (p < 0.05), thereby reducing the loss of the soil carbon pool and the rate of CO 2 production. In addition, soil CO2 Its generation is negatively correlated with the expression of the fermentation function; chloroplast represents the ecological function of oxygen-producing photosynthetic microorganisms, which can utilize CO 2 as a carbon source, form a symbiotic relationship with plants, provide nitrogen fixation for plants, and promote plant growth; compared with the CK group, the fermentation and chloroplast functions in the RB group were significantly enriched (p<0.05).

[0074] The relevant indicators of photosynthesis and soil carbon sequestration capacity of the OP group and the OCK group were tested, and the results are shown in Table 3.

[0075] Table 3 Data of relevant indicators of photosynthesis and soil carbon sequestration capacity of the OP group and the OCK group

[0076] Treatment group OCK group OP group Total chlorophyll (mg / g) 3.1021 2.4150 Starch (mg / g DW) 183.5795 210.4414 Sucrose (mg / g FW) 1.7434 1.9045 <![CDATA[H 2 O 2 (μmol / g fresh weight)]]> 0.2147 0.3684 Soil invertase (mg glucose / g soil / d) 0.3226 0.5732 Soil β-glucosidase (μg PNP / g soil / h) 14.6430 22.5971 AWCD value 0.4677 0.6015

[0077] As can be seen from Table 3, compared with the OCK group, the total chlorophyll content in the leaves of Solanum nigrum in the OP group decreased, the utilization of starch and sucrose decreased, the degree of oxidative damage increased, the activities of soil sucrase and β-glucosidase both increased significantly, and the AWCD value increased, that is, the photosynthetic and soil carbon sequestration capacities of plants both decreased. In addition, from the cumulative CO 2 emission, it can be seen that the total CO 2 absorption in the OP group was 200.91 g / m 2 , which was significantly different from that of RB-3, indicating that when Solanum nigrum was selected as the plant, the carbon emission reduction effect of acidic polluted soil was not ideal.

[0078] The above results comprehensively show that after applying corn straw biochar, the activities of soil sucrase and β-glucosidase both increased significantly, which would promote the transformation of the recalcitrant carbon pool to active carbon; at the same time, corn straw biochar would strengthen the overall metabolism and mineralization ability of soil organic carbon, which would instead increase the soil CO 2 emission. When Solanum nigrum was used as the planted plant, the photosynthetic and soil carbon sequestration capacities of plants both decreased. Different from the WB group and the OP group, the method of the present invention can regulate and optimize the activities of key enzymes participating in the carbon cycle in acidic polluted soil, moderately inhibit the overall carbon metabolism rate of the soil microbial community, and guide the microbiome to evolve in the direction conducive to the formation of difficult-to-decompose soil organic carbon by constructing a rice straw biochar-acidic polluted soil-ryegrass-microorganism coupled ecological system, further enhancing the soil carbon sequestration ability.

[0079] (IV) Changes in CO 2 emission from acidic polluted soil

[0080] A self-made dynamic chamber was used to detect the CO 2Concentration: The dynamic chamber is made of transparent plexiglass, with a hollow bottom, a sealed top, and pipelines externally connected to the intake and outlet of a pumped CO2 photodetector at the sides and top respectively to form a gas passage. A water seal groove is placed under the chamber to ensure airtightness. The detection time is fixed at 9:00 - 11:00 in the morning, and the CO 2 concentration in the system is measured at 0, 30, and 60 minutes after sealing. The CO 2 concentration in the system is monitored on the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 10th, 12th, 14th, 16th, 18th, 20th, 22nd, 26th, 30th, 35th, 40th, 45th, 50th, and 60th days respectively.

[0081] Calculation of CO 2 flux and cumulative amount in the system:

[0082]

[0083] In formula (1), F is the flux rate of CO 2 (mg·m -2 ·h -1 ); ρ represents the density of CO 2 under standard conditions (kg·m -3 ); V is the volume of the static chamber (m 3 ); A is the bottom area of the chamber (m 2 ); P is the atmospheric pressure in the system; P 0 is the standard atmospheric pressure; dC / dt is the slope of the change in CO 2 content with time (ppm), obtained by linearly fitting the CO 2 concentration and sampling time. When the regression fitting coefficient is R 2 > 0.9, it is considered valid; T is the average temperature of the static chamber during gas sampling (°C).

[0084]

[0085] In formula (2), E is the cumulative emission amount of CO 2 (mg·m -2 ); t is the sampling time.

[0086] Figure 10 This is the dynamic change trend diagram of the CO 2 flux rate in acidic contaminated soil under different treatment methods in Example 1 of the present invention. Figure 11 This is the total emission diagram of CO 2 in acidic contaminated soil under different treatment methods in Example 1 of the present invention. It can be seen from Figure 10 that during the period of 1 - 10 days, the CO 2 emitted in the acidic contaminated soil system is more than the CO 2should be high. Starting from the 10th day, the absorption of CO in the acidic polluted soil system is greater than the emission, and the minimum peak of the CO flux appears on the 30th day. Specifically, during the seed germination and seedling emergence periods (the 1st - 10th days), the CO emission fluxes of the CK group are lower than those of the experimental groups applying rice straw biochar (RB - 1 group, RB - 2 group, RB - 3 group); starting from the 10th day, the CO emissions of the CK group are significantly higher than those of the experimental groups applying rice straw biochar (RB - 1 group, RB - 2 group, RB - 3 group), and the change in the RB - 3 group is the most obvious. As can be seen from 2 The absorption of CO 2 in the acidic polluted soil system is greater than the emission starting from the 10th day, and the minimum peak of the CO 2 flux appears on the 30th day. Specifically, during the seed germination and seedling emergence periods (the 1st - 10th days), the CO 2 emission fluxes of the CK group are lower than those of the experimental groups applying rice straw biochar (RB - 1 group, RB - 2 group, RB - 3 group); starting from the 10th day, the CO Figure 11 emissions of the CK group are significantly higher than those of the experimental groups applying rice straw biochar (RB - 1 group, RB - 2 group, RB - 3 group), and the change in the RB - 3 group is the most obvious. As can be seen from 2 it can be seen that compared with the CK group, the total CO 2 emissions in the systems of the RB - 1 group, RB - 2 group and RB - 3 group are significantly reduced by 37.00% - 115.64% (p < 0.05), and negative growth of CO 2 emission is achieved during the entire restoration period. In addition, the total CO 2 absorption in the acidic polluted soil system of the WB group is only 258.64 g / m

[0087] For the method of the present invention, when the mass ratio of rice straw biochar to acidic polluted soil is 0.001 - 0.01∶1, the purpose of carbon emission reduction in acidic polluted soil can be achieved; further, when the mass ratio of rice straw biochar to acidic polluted soil is optimized to 0.005 - 0.01∶1, a better carbon emission reduction effect in acidic polluted soil can be achieved, especially when the mass ratio of rice straw biochar to acidic polluted soil is 0.01∶1, the carbon emission reduction effect is the best.

[0088] (V) Degree of alleviation of Cd pollution in acidic soil

[0089] The bioavailability of Cd in soil reflects its influence degree on plant absorption, environmental toxicity, soil microbial activity and ecological risk. Figure 12 This is the content change diagram of bio - available Cd in acidic polluted soil under different treatment methods in Example 1 of the present invention. As can be seen from Figure 12 it, compared with the original soil (original acidic polluted soil), the content of bio - available Cd in the soil with RB added is reduced by 31.61% - 45.80% (p < 0.05).

[0090] In summary, the method of the present invention can simultaneously enhance plant photosynthesis and soil carbon sequestration ability by constructing a coupled rice straw biochar - acidic polluted soil - ryegrass - microorganism ecological system (as Figure 13 shown), thereby reducing CO2 emission, and to a certain extent, reduces the toxicity risk of heavy metals in acidic polluted soil.

[0091] As mentioned above, it is only the preferred embodiment of the present invention, and it does not impose any formal restrictions on the present invention. Although the present invention has been disclosed above with the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for reducing carbon emissions from acidic contaminated soil based on a coupled ecosystem, characterized in that: The following steps are involved: Rice straw biochar is added to acidic contaminated soil, and plants are planted. When the plants are cultivated to maturity, the negative growth of the cumulative amount of CO2 emissions and the restoration of the acidic contaminated soil are achieved by simultaneously satisfying the enhancement of the plant's photosynthesis capacity and the soil's carbon fixation capacity; the plant is perennial ryegrass.

2. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecosystem according to claim 1, characterized in that: The mass ratio of the rice straw biochar to the acidic contaminated soil is 0.001-0.01:

1.

3. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecosystem according to claim 2, characterized in that: The mass ratio of the rice straw biochar to the acidic contaminated soil is 0.005-0.01:

1.

4. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecosystem according to claim 3, characterized in that: The rice straw biochar is prepared by the following method: under oxygen-limited conditions, rice straw is pyrolyzed to obtain rice straw biochar; the pyrolysis temperature is 450°C to 500°C, the pyrolysis time is 2h to 3h, and the heating rate during the pyrolysis process is 5°C / min to 10°C / min.

5. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecosystem according to claim 4, characterized in that: The rice straw is further processed as follows before use: harvesting the rice when it is mature but not completely dried to ensure its nutritional value and structural integrity, removing leaves and sheaths, washing the rice straw, drying it to a moisture content of 10% to 15%, crushing it, and sieving it; the drying temperature is 70° C., and the sieving is through a 100-mesh sieve.

6. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecological system according to any one of claims 1 to 5, characterized in that: The pH value of the acidic contaminated soil is 4-5, the acidic contaminated soil contains heavy metals, the concentration of the heavy metals in the acidic contaminated soil is 5mg / kg-10mg / kg, and the heavy metals include cadmium.

7. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecological system according to any one of claims 1 to 5, characterized in that: The perennial ryegrass is planted using ryegrass seeds, and the sowing amount of the ryegrass seeds is 2g to 3g per kilogram of acidic polluted soil.

8. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecosystem according to claim 7, characterized in that: The ryegrass seeds also include the following treatments before use: screening, disinfecting and soaking the ryegrass seeds; the specific process of the screening is: selecting ryegrass seeds with similar sizes and full grains and placing them in a sodium chloride solution, screening them, and removing floating seeds and impurities; the mass fraction of the sodium chloride solution is 10%; the specific process of the disinfection is: soaking the screened ryegrass seeds in a hydrogen peroxide aqueous solution for 15 minutes, washing them, and drying them; the soaking is carried out under stirring conditions, and the mass fraction of the hydrogen peroxide aqueous solution is 3%; the specific process of the soaking is: soaking the disinfected ryegrass seeds in water at 40°C to 50°C for 10 minutes to 15 minutes, and then soaking them in water at 15°C to 20°C for 12 hours.

9. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecological system according to any one of claims 1 to 5, characterized in that: The cultivation time is 45 to 60 days; during the entire cultivation stage, watering is performed regularly, and the watering frequency is 1 to 2 days, so as to keep the soil moisture at 60% to 70% of the maximum field water holding capacity; from the 0th to 14th day of the cultivation, the soil is loosened every other week and then watered with improved Holland's nutrient solution; The method further comprises the following treatments after the rice straw biochar is added to the acidic contaminated soil: standing for 10 to 15 days to ensure homogenization between the rice straw biochar and the soil, watering with nutrient solution, turning the soil to enhance the air permeability and water permeability of the soil, and starting planting when the soil surface is dry; the nutrient solution is a diluted modified Holland's nutrient solution, and the preparation process of the diluted modified Holland's nutrient solution is: mixing the modified Holland's nutrient solution and water, and the volume ratio of the modified Holland's nutrient solution to water is 1:

200.

10. The method for reducing carbon emissions from acidic contaminated soil based on a coupled ecological system according to any one of claims 1 to 5, characterized in that: The number of soil microbial species in the coupled ecological system is 788-870, and the bacterial community structure is mainly composed of Chloroflexi, Actinobacteria, Proteobacteria and Acidobacteria.

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