Method for promoting carbon emission reduction and carbon fixation in wetland soil by utilizing biochar combined ferrihydrite

Abstract

The invention discloses a method for promoting carbon emission reduction and carbon fixation in wetland soil by using biochar and ferrihydrite, which comprises the following steps: mixing biochar, ferrihydrite and wetland soil to complete the treatment of the wetland soil. According to the method, the biochar and the ferrihydrite are added into the wetland soil, the combined soil improvement effect of the biochar and the ferrihydrite can be utilized, emission of methane and carbon dioxide is inhibited, the overall emission reduction effect of greenhouse gas is good, conversion of organic matter in the stable direction is promoted, and the carbon fixing amount and the carbon fixing effect are improved; and the double-carbon target can be realized. Meanwhile, the method for promoting carbon emission reduction and carbon immobilization in the wetland soil by utilizing the charcoal combined ferrihydrite has the advantages of simple process, convenience in operation, low cost, environmental friendliness and the like, and is convenient for industrial application, high in use value and good in application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and relates to a method for carbon emission reduction and carbon fixation in wetland soil, specifically to a method for promoting carbon emission reduction and carbon fixation in wetland soil by using biochar combined with ferrihydrite. Background Art

[0002] Wetland soil is an important source of greenhouse gases, including not only methane but also carbon dioxide. Therefore, effectively reducing the emissions of greenhouse gases in wetland soil is of great significance for achieving the goal of carbon neutrality.

[0003] Biochar is the high-temperature pyrolysis product of waste biomass in an oxygen-limited environment, which has an inhibitory effect on greenhouse gas emissions and has great potential in alleviating global climate change. However, many existing studies focus on the promoting effect of biochar application on reducing methane emissions, while ignoring that biochar itself, as a carbon material, can increase the organic carbon easily utilized by microorganisms in the soil, and it has a significant stimulating effect on carbon dioxide emissions. Therefore, it is difficult to effectively reduce the overall emissions of greenhouse gases. At the same time, when biochar is applied alone, it is also difficult to effectively convert the unstable organic carbon easily utilized by microorganisms in the soil into organic carbon with a stable structure, and there are still defects such as low carbon fixation amount and poor carbon fixation effect. Considering from a long-term perspective, the un-fixed organic carbon is still easily utilized and metabolized by microorganisms and converted into greenhouse gases and discharged, which further increases the emissions of greenhouse gases and is not conducive to alleviating the severe greenhouse effect currently faced globally. Therefore, obtaining a method that can simultaneously promote carbon emission reduction and carbon fixation is of great significance for effectively alleviating the greenhouse effect. 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 promoting carbon emission reduction and carbon fixation in wetland soil by using biochar combined with ferrihydrite, which has the advantages of simple process, convenient operation, low cost, and environmental friendliness.

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

[0006] A method for promoting carbon emission reduction and carbon fixation in wetland soil by using biochar combined with ferrihydrite, comprising the following steps:

[0007] S1. Mix biochar, ferrihydrite with wetland soil to complete the treatment of wetland soil.

[0008] In the above method, further improved, in step S1, the mass ratio of the biochar to the wetland soil is 0.5% - 2%.

[0009] In the above method, further improved, in step S1, the mass ratio of the biochar to the wetland soil is 0.8% - 1.5%.

[0010] In the above method, further improved, in step S1, the wetland soil is paddy soil; the biochar is prepared by pyrolyzing biomass materials.

[0011] In the above method, further improved, in step S1, the preparation method of the biochar includes the following steps: under a nitrogen protection atmosphere, at a heating rate of 5°C / min - 10°C / min, heat the biomass material to 400 - 800°C for oxygen-limited high-temperature pyrolysis for 0.5 - 2 h, crush and pass through a 100 - 200 mesh sieve, wash, and dry to obtain biochar; the biomass material is rice straw.

[0012] In the above method, further improved, in step S1, the addition amount of ferrihydrite is 0.1 mmol of ferrihydrite added per gram of wetland soil based on dry weight.

[0013] In the above method, further improved, in step S1, the preparation method of the ferrihydrite includes the following steps: mix the iron salt with water to obtain an iron salt solution; adjust the pH value of the iron salt solution to 7.0 - 7.2, centrifuge, wash, and freeze-dry to obtain ferrihydrite; the concentration of the iron salt in the iron salt solution is 0.2 mol / L - 0.4 mol / L; the iron salt is Fe(NO3)3·9H2O; the rotation speed of the centrifuge is 4000 r / min - 8000 r / min; the number of washing times is 3 - 5 times.

[0014] In the above method, further improved, in step S1, after mixing the biochar, ferrihydrite and wetland soil to obtain a wetland soil mixture, the following treatment is also included:

[0015] S2. Cultivate the wetland soil mixture.

[0016] In the above method, further improved, in step S2, the cultivation is carried out under anaerobic conditions; the cultivation temperature is 25°C - 35°C; the cultivation time is 12 days - 90 days.

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

[0018] (1)In view of the defects in the existing biochar-based methods for carbon emission reduction and carbon sequestration in soil, such as poor greenhouse gas emission reduction effect, small carbon sequestration amount, and poor carbon sequestration effect, the present invention creatively proposes a method for promoting carbon emission reduction and carbon sequestration in wetland soil by using biochar in combination with ferrihydrite. By adding biochar and ferrihydrite to wetland soil, it is possible to simultaneously reduce the emissions of methane and carbon dioxide, with a good overall greenhouse gas emission reduction effect. Moreover, it can promote the transformation of organic matter in a stable direction, which is conducive to increasing the carbon sequestration amount and carbon sequestration effect, and can achieve the "dual carbon" goal. Specifically, on the one hand, under the combined action of biochar and ferrihydrite, the redox conditions of wetland soil can be effectively regulated, and the process of dissimilatory iron reduction in the anaerobic environment can be promoted. This process can compete for electrons with the methanogenesis process, enabling the electrons that originally flowed to methanogens to be utilized by dissimilatory iron-reducing bacteria. As a result, methane emissions can be reduced, and at the same time, the abundance of dissimilatory iron-reducing bacteria can be significantly increased. Furthermore, the relative abundance of methanogens in wetland soil can be inhibited, reducing the abundance of methanogens, which is beneficial for reducing methane emissions, achieving greenhouse gas emission reduction, and significantly alleviating the greenhouse effect. On the other hand, under the combined action of biochar and ferrihydrite, the dissolved organic matter in wetland soil can be promoted to transform in a stable direction. In particular, under the promotion of biochar, the combination of ferrihydrite and the organic matter in wetland soil can be accelerated to form more stable iron-bound organic carbon, thereby protecting the organic carbon in the soil from being metabolized and utilized by microorganisms. As a result, the carbon sequestration amount in wetland soil can be increased, the carbon sequestration effect can be improved, and at the same time, the emissions of methane and carbon dioxide can be further reduced, achieving greenhouse gas emission reduction as a whole. At the same time, the method for promoting carbon emission reduction and carbon sequestration in wetland soil by using biochar in combination with ferrihydrite of the present invention also has the advantages of simple process, convenient operation, low cost, and environmental friendliness, facilitating industrial application, having high use value, and good application prospects.

[0019] (2) In the present invention, by optimizing the mass ratio of biochar to wetland soil to be 0.5% - 2%, especially when the mass ratio of biochar to wetland soil is 0.8% - 1.5%, the emission reduction of greenhouse gases can be maximally achieved. The reasons are as follows: On the one hand, the preparation of biochar requires pyrolysis under high-temperature conditions, and its production process itself consumes a certain amount of electrical energy and emits by-products such as biogas and bio-oil. Therefore, by optimizing the dosage of biochar, the impact of the biochar preparation process on the environment can be reduced to a certain extent, including reducing the emission of greenhouse gases during the preparation process. On the other hand, biochar can reduce the emission of greenhouse gas methane by affecting the soil microbial community. However, biochar itself is a material with a high carbon content. Adding biochar can increase the organic carbon concentration in the soil, promote the metabolism of organic carbon by some microorganisms in the soil, and then stimulate the generation of carbon dioxide. Therefore, if a large amount of biochar is added, it is not conducive to controlling the total emission of greenhouse gases. At the same time, in the present invention, by optimizing the addition amount of ferrihydrite to be 0.1 mmol of ferrihydrite added per gram of wetland soil based on dry weight, while increasing the iron element content in the soil, the destructive impact on the soil material composition can be minimized, so that the emissions of methane and carbon dioxide can be significantly reduced simultaneously on the premise of improving the soil quality, which is conducive to achieving the overall emission reduction of greenhouse gases.

[0020] (3) In the present invention, the biochar used is made from biomass materials, and these biomass materials include rice straw. By converting the biomass materials into biochar materials, the organic carbon in the biomass materials can be converted into carbon materials with stable structures, which is an effective way of carbon fixation. Moreover, biochar, as a material with a high carbon content, adding it back to the paddy field can also improve the soil properties, reduce greenhouse gas emissions, enhance the soil carbon sequestration capacity, increase the yield and income of crops such as rice, and at the same time help solve the problem of agricultural waste disposal, realize the recycling of biomass materials, and improve the resource utilization rate of agricultural waste. Description of the Drawings

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

[0022] Figure 1 It is a dynamic change diagram of the accumulation concentration of divalent iron in paddy soil under different treatment conditions in Example 1 and Comparative Example 1 of the present invention.

[0023] Figure 2 It is a comparison diagram of the cumulative amounts of CH4 and CO2 in paddy soil under different treatment conditions in Example 1 and Comparative Example 1 of the present invention.

[0024] Figure 3This is the dynamic change graph of the concentration of dissolved organic matter in paddy soil under different treatment conditions in Example 1 of the present invention and Comparative Example 1.

[0025] Figure 4 This is the control graph of the relative contribution rate to the total fluorescence under different treatment conditions in Example 1 of the present invention and Comparative Example 1.

[0026] Figure 5 This is the change graph of the microbial community at the phylum level in paddy soil under different treatment conditions in Example 1 of the present invention and Comparative Example 1.

[0027] Figure 6 This is the change graph of the relative abundance at the genus level of the archaeal community in paddy soil under different treatment conditions in Example 1 of the present invention and Comparative Example 1. Detailed implementation mode

[0028] 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 examples are all commercially available.

[0029] Example 1:

[0030] A method for promoting carbon emission reduction and carbon fixation in wetland soil by using biochar combined with ferrihydrite, specifically, the paddy soil is treated with biochar and ferrihydrite in combination, including the following steps:

[0031] S1. According to the mass ratio of biochar to wetland soil (dry weight) being 0, 0.5%, 1%, 2%, and the addition amount of ferrihydrite being 0.1 mmol of ferrihydrite added per gram of wetland soil (dry weight), mix biochar, ferrihydrite with paddy soil (soil for growing rice). Specifically, in a 120 mL serum bottle, add 20 mL of deionized water for sterilization treatment. Add different proportions of biochar to the paddy soil, add ferrihydrite, and after mixing, add it to the serum bottle to obtain a wetland soil mixture. In this step, the mass ratio of biochar to wetland soil (dry weight) is 0, 0.5%, 1%, 2%, numbered as Soil+Fh, Soil+Fh+0.5% BC, Soil+Fh+1% BC, Soil+Fh+2% BC in sequence.

[0032] S2. Cultivate the wetland soil mixture, specifically: cover it with a sterilized butyl rubber stopper, compact the aluminum lid for sealing, replace the gas in the top space of the serum bottle with N2 to ensure that the serum bottle reaches an anaerobic state at normal pressure, and place the serum bottle in an incubator and let it stand for cultivation at 30°C for 60 days to complete the treatment of the wetland soil.

[0033] In Example 1, the biochar used was prepared by the following method, which includes the following steps: Under a nitrogen protection atmosphere, the rice straw was heated to 600 °C at a heating rate of 5 °C / min for oxygen-limited high-temperature pyrolysis treatment for 1 h, crushed, passed through a 100-mesh sieve, washed, and dried to obtain biochar.

[0034] In Example 1, the ferrihydrite used was prepared by the following method, which includes the following steps: 20.2 g of Fe(NO3)3·9H2O was mixed with 250 mL of water, and the pH value of the mixed solution was adjusted to 7.2 with a 1 M sodium hydroxide solution. It was centrifuged at 8000 r / min, the solid phase was collected, washed 4 times with water, and freeze-dried to obtain ferrihydrite.

[0035] Comparative Example 1:

[0036] A method for promoting carbon emission reduction and carbon fixation in wetland soil using biochar is basically the same as Example 1, except that in Comparative Example 1, only biochar was used to treat paddy soil, including the following steps:

[0037] S1. According to the mass ratio of biochar to wetland soil (dry weight) of 0, 0.5%, 1%, and 2%, the biochar prepared in Example 1 was mixed with paddy soil (soil for growing rice). Specifically, in a 120 mL serum bottle, 20 mL of deionized water was added for sterilization treatment. Different proportions of biochar were added to the paddy soil, and after mixing, it was added to the serum bottle to obtain a wetland soil mixture. In this step, the mass ratio of biochar to wetland soil (dry weight) was 0, 0.5%, 1%, and 2%, numbered as Control, Soil+0.5%BC, Soil+1% BC, and Soil+2% BC in sequence.

[0038] S2. The wetland soil mixture was cultured. Specifically: The sterilized butyl rubber stopper was covered, the aluminum lid was compacted and sealed, and the gas in the top space of the serum bottle was replaced with N2 to ensure that the serum bottle reached an anaerobic state at normal pressure. The serum bottle was placed in an incubator and statically cultured at 30 °C for 60 days to complete the treatment of the wetland soil.

[0039] The Fe(II) concentration at each sampling point was measured on the 0th, 1st, 6th, 12th, 20th, 35th, and 60th days of the culture, and the results are as Figure 1 shown.

[0040] Figure 1 This is the dynamic change diagram of the accumulation concentration of divalent iron in paddy soil under different treatment conditions in Example 1 and Comparative Example 1 of the present invention. From Figure 1It can be seen that, compared with Comparative Example 1, in Example 1 of the present invention, after adding biochar and ferrihydrite and culturing for 6 days, the concentration of Fe(II) in the soil increased significantly. In particular, after culturing for 60 days, the concentration of Fe(II) in the soil in each treatment of the experimental group increased to 71.84±0.85 mmol / g dry soil (Soil+Fh+0.5% BC), 76.06±1.90 mmol / g dry soil (Soil+Fh+1% BC) and 76.56±2.21 mmol / g dry soil (Soil+Fh+2% BC) respectively. This shows that the addition of ferrihydrite can increase the total iron content in the soil, and then provide more iron that can be utilized by dissimilatory iron-reducing bacteria, and strengthen the process of dissimilatory iron reduction. In this process, ferrihydrite can compete with the methanogenesis process for electrons, so that the electrons originally flowing to methanogens are utilized by dissimilatory iron-reducing bacteria, thereby reducing methane emissions and promoting the reduction of greenhouse gases. By comparison, in the present invention, by adding biochar and ferrihydrite to paddy soil at the same time, the process of microbial dissimilatory iron reduction can be accelerated, and the accumulation concentration of Fe(II) in the soil can be significantly increased. This shows that the present invention can effectively regulate the redox conditions of wetland soil by using the combined action of biochar and ferrihydrite, and promote the dissimilatory iron reduction process under anaerobic conditions. This process can compete with the methanogenesis process for electrons, so that the electrons originally flowing to methanogens are utilized by dissimilatory iron-reducing bacteria, reducing methane emissions. At the same time, the abundance of dissimilatory iron-reducing bacteria can be significantly increased, and then the relative abundance of methanogens in wetland soil can be inhibited, reducing the abundance of methanogens, which is beneficial to reducing methane emissions, achieving the reduction of greenhouse gases, and significantly alleviating the greenhouse effect.

[0041] At the 12th day and 60th day of culturing, the cumulative amounts of CH4 and CO2 were detected, and the results are as Figure 2 shown.

[0042] Figure 2 It is a control chart of the cumulative amounts of CH4 and CO2 in paddy soil under different treatment conditions in Example 1 of the present invention and Comparative Example 1. Figure 2 In it, -Fh indicates that ferrihydrite is not added, and +Fh indicates that ferrihydrite is added. From Figure 2It can be seen that in Comparative Example 1, after 60 days of anaerobic cultivation, in the paddy soils added with different proportions of biochar, the cumulative CH4 amount was between 2.83±0.09 and 3.11±0.22 mmol / L, and the inhibition efficiencies for the cumulative CH4 amount were 1.20% (0.5% BC), 9.10% (1% BC), and 6.11% (2% BC), respectively. However, the added biochar could promote the accumulation of carbon dioxide. After 60 days of anaerobic cultivation in Comparative Example 1, the total carbon dioxide emissions (2% BC) increased by 21.90%. In contrast, in Example 1, after 60 days of anaerobic cultivation, the cumulative CH4 amount in the rice soil treated with biochar and ferrihydrite was between 1.98±0.12 mmol / L and 2.35±0.11 mmol / L, and the inhibition rate of CH4 reached 24.69% - 32.28%. Similarly, after adding biochar and ferrihydrite, in the rice soil treated with biochar and ferrihydrite, the accumulation of carbon dioxide could be effectively inhibited, and the inhibition rate of the cumulative CO2 amount reached 34.24% - 43.06%. Thus, it can be seen that in the present invention, the combined application of biochar and ferrihydrite can significantly inhibit the generation of greenhouse gases. In particular, when the mass ratio of biochar to wetland soil (dry weight) is 2%, corresponding to “Soil+Fh+2% BC”, the inhibition effect on greenhouse gases is the most significant, and it can reduce the accumulation amounts of both methane and carbon dioxide at the same time. The above results show that in the present invention, under the combined action of biochar and ferrihydrite, the transformation of dissolved organic pollutants in wetland soil can be promoted towards a stable direction. In particular, under the promotion of biochar, the combination of ferrihydrite and the organic matter in wetland soil can be accelerated to form more stable iron-bound organic carbon, thereby increasing the carbon fixation amount in wetland soil and improving the carbon fixation effect.

[0043] On the 0th, 1st, 6th, 12th, 20th, 35th, and 60th days of cultivation, the concentrations of dissolved organic matter at each sampling point were detected, and the results are as Figure 3 shown.

[0044] Figure 3 This is the dynamic change diagram of the concentration of dissolved organic matter in the rice soil under different treatment conditions in Example 1 and Comparative Example 1 of the present invention. From Figure 3It can be seen that from day 0 to day 6, in the blank group, the concentration of dissolved organic matter (DOM) first increased sharply to 494.50±20.89 μg C / g dry soil, then showed a downward trend in the following 14 days, and finally entered a 40-day stable stage (about 306.33±11.69 μg C / g dry soil). The treatments with different biochar application ratios showed a similar trend to the blank group, and the peak DOM concentrations on day 6 all decreased, being 442.83±14.70 (0.5% BC), 457.30±26.81 (1% BC), and 449.33±19.38 (2% BC) μg C / g dry soil respectively. In addition, in the group with only ferrihydrite added (Soil+Fh), the concentration of DOM reached the highest point of 359.73±17.46 μg C / g dry soil on day 12, which was about 27.25% lower than that of the blank group. In the experimental groups with biochar and ferrihydrite added jointly (Example 1), the peak DOM concentrations were 358.03±10.39 μg C / g dry soil (Soil+Fh+0.5% BC), 339±53.96 μg C / g dry soil (Soil+Fh+1% BC), and 308.00±1.15 μg C / g dry soil (Soil+Fh+2% BC) respectively. It can be seen that compared with the control group (Comparative Example 1), in the groups with biochar and ferrihydrite applied jointly, the peak DOM concentration was significantly reduced, and its change process was also more stable. This is because the addition of ferrihydrite can quickly combine with the organic matter in the soil to form stable iron-carbon coupling in the early stage of cultivation, reducing the content of dissolved organic matter, and further reducing the total amount of dissolved organic matter that can be metabolized and utilized by microorganisms, promoting the stability of soil carbon and inhibiting the emission of greenhouse gases. At the same time, by optimizing the dosage of biochar, the generation of iron-carbon coupling was further promoted, and the generation of iron-bound organic carbon was strengthened. Therefore, the application of biochar combined with ferrihydrite effectively protected soil organic carbon and promoted soil carbon fixation and carbon emission reduction.

[0045] Parallel factor (PARAFAC) analysis was further performed on the three-dimensional fluorescence spectroscopy data. According to the split-half analysis method, the components of DOM were divided into five parts, and the selected five components were compared with previous studies. Component 1 was considered to be humic-like substances produced by microbial metabolic activities, that is, low-molecular-weight aliphatic substances. Component 2 was humic-like substances, mainly low-aromaticity and low-molecular-weight substances, while Component 3 was terrestrial humic substances with high aromaticity and high molecular weight. In addition, Components 4 and 5 had the characteristics of tyrosine-like and tryptophan-like components and were easily utilized by microorganisms. The maximum fluorescence intensity (Fmax) of each component was normalized by the DOM concentration, and then the relative abundance was calculated by dividing its Fmax by the sum of the Fmax of all components.

[0046] Figure 4This is a control chart of the relative contribution rates of total fluorescence in Example 1 and Comparative Example 1 of the present invention under different treatment conditions. Figure 4 Among them, the corresponding samples are before anaerobic cultivation (day 0) and after anaerobic cultivation (day 60). It can be Figure 4 seen that the relative contents of these five fluorescence components (Component 1 - Component 5) are different in different samples and change with the cultivation time. On day 0, the contents of humus-like substances (Component 1, Component 2, and Component 3) in the experimental group (Example 1) were lower than those in the blank group and the control group (Comparative Example 1). Compared with the dissolved organic matter components on day 0, the humus-like substances in the treatment without added ferrihydrite increased by 24.93% - 31.93% after cultivation. The relative abundances of Component 4 and Component 5 in the "Soil + 0.5% BC", "Soil + 1% BC", and "Soil + 2% BC" treatments were respectively 1.59%, 1.96%, and 3.37% lower than those in the blank group on day 60. In addition, the experimental group with added ferrihydrite increased the percentage of humic-like substances by 26.09% - 33.03%, while the treatments with only different proportions of biochar added metabolized less dissolved organic matter and only increased the humic-like substances by 16.70% - 18.05%. Thus, it can be seen that in an anaerobic environment, microorganisms will preferentially metabolize unstable organic carbon and transform it into more stable organic carbon. The dissimilatory iron reduction process will accelerate the metabolism of unstable organic carbon by microorganisms and convert it into stable humic-like substances. Ferrihydrite will preferentially form an iron-carbon coupling with stable organic carbon and exist in soil carbon in the form of adsorption and coprecipitation, promoting the fixation of soil organic carbon and serving as a "temporary carbon sink" for organic carbon. The addition of biochar accelerates this coupling process. Generally speaking, the combination of biochar and ferrihydrite can promote the transformation of organic carbon in paddy soil towards a stable direction and achieve carbon fixation.

[0047] On the 1st day and the 60th day of cultivation, samples were taken to analyze the microbial community composition in the samples to determine the microorganisms that may promote the iron reduction process and methane production during the improvement process of biochar and ferrihydrite. According to 16S rRNA gene sequencing, a total of 71 phyla and 1143 genera were classified, and the results are as Figure 5 、 Figure 6 shown.

[0048] Figure 5 This is a graph showing the changes in the microbial community at the phylum level in paddy soil under different treatment conditions in Example 1 and Comparative Example 1 of the present invention. Figure 5 Among them, the color intensity in each unit represents the abundance of each phylum in different treatments. The samples of different treatments all have Firmicutes, Proteobacteria, Actinobacteria, and Planctomycetota as the dominant phyla. It can be Figure 5It can be seen that after 60 days of anaerobic culture, the relative abundances of Bacteroidota and Desulfobacterota increased significantly, while the proportions of Proteobacteria, Actinobacteria, Planctomycetota, and Acidobacteriota all decreased (p < 0.05). In addition, compared with the treatment without ferrihydrite addition, after adding ferrihydrite, the relative abundance of Desulfobacterota in the anaerobic environment increased from 1.06% ± 0.08% to 1.44% ± 0.11%. This indicates that the combination of biochar and ferrihydrite stimulated the growth of dissimilatory iron-reducing bacteria, thereby accelerating the dissimilatory iron reduction process in the anaerobic environment, promoting the competition between dissimilatory iron-reducing bacteria and methanogens for electron acceptors, and thus reducing greenhouse gas emissions.

[0049] Figure 6 This is a graph showing the changes in the relative abundances of the archaeal community at the genus level in rice paddy soil under different treatment conditions in Example 1 and Comparative Example 1 of the present invention. From Figure 6It can be seen that on the 1st day and the 60th day, there are obvious differences in the dominant bacterial genera in the archaeal community composition. Methanobacterium is the dominant bacterial genus in all groups, followed by Methanocella, norank in Bathyarchaeia, Methanosarcina, and Rice Cluster I (the top 5 among all archaeal genera). The relative abundance of norank in Bathyarchaeia decreased significantly from 20.77% ± 8.04% to 13.12% ± 4.36%. However, the relative abundances of Methanosarcina and Methanosaeta increased significantly from 9.39% ± 2.99% and 6.82% ± 2.07% on the 0th day (p < 0.05) to 13.35% ± 2.85% and 9.57% ± 2.33% after 60 days of cultivation. Compared with the four groups without added ferrihydrite, the addition of ferrihydrite significantly increased the proportions of Rice Cluster I and Methanosaeta, from 9.29% ± 0.67% and 7.57% ± 1.10% to 12.13% ± 2.45% and 11.57% ± 0.87% respectively, while decreasing the relative abundances of norank in Nitrososphaeraceae and Methanosarcina, from 16.34% ± 3.31% to 9.90% ± 2.38% (p < 0.05), and from 15.41% ± 1.48% to 11.28% ± 2.34%. Norank in Nitrososphaeraceae and Methanosarcina have been proven to have a significant positive correlation with methane production. It can be seen that the addition of ferrihydrite significantly inhibits the relative abundance of methanogens, thereby contributing to the reduction of methane emissions in the soil environment, making a significant contribution to promoting soil carbon emission reduction, carbon fixation, and alleviating global climate change.

[0050] From the above results, it can be seen that in the method of the present invention, the combined application of biochar and ferrihydrite can significantly reduce the emissions of greenhouse gases in paddy soil (34.24% - 43.06% CO2 and 24.69% - 32.28% CH4), can promote greenhouse gas emission reduction, and can promote the fixation of organic carbon. At the same time, the method of the present invention for promoting carbon emission reduction and carbon fixation in wetland soil by combining biochar and ferrihydrite also has the advantages of simple process, convenient operation, low cost, environmental friendliness, etc., is convenient for industrial application, has high use value, and good application prospects.

[0051] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, 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 equivalent embodiments 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 promoting carbon emission reduction and carbon fixation in wetland soil by using biochar combined with ferrihydrite, characterized in that, It includes the following steps: S1. Mix biochar, ferrihydrite and wetland soil to complete the treatment of wetland soil.

2. The method according to claim 1, wherein In step S1, the mass ratio of the biochar to the wetland soil is 0.5% to 2%.

3. The method according to claim 2, wherein In step S1, the mass ratio of the biochar to the wetland soil is 0.8% to 1.5%.

4. The method according to claim 3, characterized in that In step S1, the wetland soil is paddy soil; the biochar is prepared by pyrolyzing biomass materials.

5. The method according to claim 4, characterized in that, In step S1, the preparation method of the biochar includes the following steps: Under a nitrogen protection atmosphere, at a heating rate of 5°C / min to 10°C / min, heat the biomass material to 400 to 800°C for oxygen-limited high-temperature pyrolysis treatment for 0.5 to 2 h, crush and sieve through a 100- to 200-mesh sieve, wash, and dry to obtain biochar; the biomass material is rice straw.

6. The method according to any one of claims 1 to 5, characterized in that In step S1, the addition amount of ferrihydrite is 0.1 mmol of ferrihydrite added per gram of wetland soil in terms of dry weight.

7. The method according to claim 5, characterized in that In step S1, the preparation method of the ferrihydrite includes the following steps: Mix the iron salt with water to obtain an iron salt solution; adjust the pH value of the iron salt solution to 7.0 to 7.2, centrifuge, wash, and freeze-dry to obtain ferrihydrite; the concentration of the iron salt in the iron salt solution is 0.2 mol / L to 0.4 mol / L; the iron salt is Fe(NO3)3·9H2O; the rotation speed of the centrifuge is 4000 r / min to 8000 r / min; the number of washing times is 3 to 5 times.

8. The method according to any one of claims 1 to 5, characterized in that In step S1, after mixing the biochar, ferrihydrite and wetland soil to obtain a wetland soil mixture, the following treatment is also included: S2. Cultivate the wetland soil mixture.

9. The method according to claim 8, characterized in that, In step S2, the cultivation is carried out under anaerobic conditions; the cultivation temperature is 25°C to 35°C; the cultivation time is 12 days to 90 days.

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