A method for improving soil carbon sequestration capacity of abandoned land on the Loess Plateau

Abstract

The present invention relates to the field of carbon fixation technology, and specifically discloses a method for improving the carbon fixation capacity of abandoned land soil in the Loess Plateau, including the preparation of a carbon fixer and the adjustment of a plant community structure; the carbon fixer is prepared from biochar, straw fragments and a composite bacterial agent according to a dosage ratio of 4-6g:2-3g:6-10mL; the composite bacterial agent is mixed with Brevibacillus nitrificans vv6, Nitrobacter vermiformis XY-01, spontaneous nitrogen-fixing bacteria MBC5 and Bradyrhizobium Qian2 according to a volume ratio of 1:1:2-3:2-4; the plant community structure adjustment includes reseeding rural potato and grass plants to reduce the number of dominant species of Asteraceae plants. The present invention can significantly improve the carbon fixation capacity of abandoned land soil in the Loess Plateau by applying a carbon fixer and optimizing the composition of the plant community, which has important practical significance for the construction of a carbon fixation and sink-enhancing vegetation restoration ecosystem, and helps ecologically fragile areas achieve the "dual carbon" goal.

Description

Technical Field

[0001] The present invention relates to the field of carbon sequestration technology, and in particular to a method for improving the carbon sequestration capacity of soil in abandoned land on the Loess Plateau. Background Art

[0002] The Loess Plateau is located in an ecologically fragile zone and a climate change sensitive area. It is one of the main battlefields for ecological protection and high-quality development in the Yellow River Basin. The vegetation coverage of the Loess Plateau has increased from 31.6% in 1999 to 62.8% in 2018. Soil erosion has been effectively controlled, the ecological environment quality has been significantly improved, and the regional carbon sink function has been significantly enhanced. The area of ​​abandoned farmland on the Loess Plateau is 5.7×10 6 hm 2 , accounting for 10.4% of the total grassland area in the region; the organic carbon sink potential of the surface soil of abandoned land can reach 8.3t / hm 2 , playing an important role in the carbon budget of the Loess Plateau and even in my country. However, the slow rate of soil carbon fixation in abandoned land has seriously restricted the effective performance of the carbon sink function of the ecosystem. The reason is the dependence of soil carbon fixation on functional microorganisms and plant functional groups. For example, biochar combined with bacterial fertilizer can increase the soil carbon pool of abandoned land by 10.62% within 30 days. In addition, the dominant plant functional group species in the late succession of the early stage of abandonment can increase the soil carbon fixation rate by 200%. Given the importance of abandoned land in maintaining the carbon sink function of the Loess Plateau, improving the soil carbon fixation capacity of abandoned land is of great significance for reducing the regional atmospheric carbon dioxide concentration, mitigating the greenhouse effect and its negative ecological impacts.

[0003] Ansai District, which belongs to Yan'an City, Shaanxi Province, is located in the hinterland of the Loess Plateau. It has a fragile ecological environment, severe soil erosion, and extremely low soil carbon content. At present, the ecological restoration in Ansai District mainly focuses on the abandonment of low-yield farmland, that is, repairing degraded land through the natural succession of vegetation after abandonment. However, long-term abandonment has a slow effect on repairing soil structure, improving soil nutrient levels, and improving soil microbial flora. In addition, there is great uncertainty in the succession of ground plant communities, resulting in the soil carbon sequestration effect of abandoned land is not obvious, and even the soil carbon storage has a downward trend 30 years after abandonment. Therefore, it is particularly important to improve the carbon sequestration and sink capacity of abandoned land soil through artificial intervention. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for improving the carbon fixation capacity of abandoned land soil on the Loess Plateau, by applying carbon fixation agents to the soil and adjusting the plant community structure to improve the carbon fixation capacity of the soil.

[0005] The present invention provides a method for improving the carbon fixation capacity of abandoned land soil on the Loess Plateau, applying a carbon fixation agent to the soil and adjusting the plant community structure;

[0006] The carbon fixer is prepared from biochar, straw shreds and composite bacterial agent in a dosage ratio of 4-6 g: 2-3 g: 6-10 mL;

[0007] The composite bacterial agent is prepared by mixing Brevibacillus nitrificans vv6, Nitrobacter veseri XY-01, autogenous nitrogen-fixing bacteria MBC5 and Bradyrhizobium Qian2 in a volume ratio of 1:1:2-3:2-4.

[0008] The adjustment of the plant community structure specifically includes reseeding leguminous plants and gramineous plants and reducing the number of dominant species of Asteraceae plants.

[0009] Furthermore, the preparation process of the nitrifying Bacillus brevis vv6 inoculant is as follows: the strain vv6 is inoculated onto an LB solid culture medium for activation, purified by 3-4 plate streaking transfers, the purified strain is inoculated into an LB liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 4 days to obtain the nitrifying Bacillus brevis vv6 inoculant.

[0010] Furthermore, the preparation process of the Nitrobacter wiese XY-01 bacterial agent is as follows: the strain XY-01 is inoculated onto HA solid culture medium for activation, purified by 3-4 plate streaking transfers, the purified strain is inoculated into HA liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 3 days to obtain the Nitrobacter wiese XY-01 bacterial agent.

[0011] Furthermore, the preparation process of the self-generating nitrogen-fixing bacteria MBC5 agent is as follows: the strain MBC5 is inoculated on a GD solid culture medium for activation, purified by transferring on a solid plate 3-4 times, the purified strain is inoculated into a GD liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 3 days to obtain the self-generating nitrogen-fixing bacteria MBC5 agent.

[0012] Furthermore, the preparation process of the Bradyrhizobium Qian2 agent is as follows: the strain Qian2 is inoculated onto a YMA solid culture medium for activation, purified by transfer on a solid plate 3-4 times, the purified strain is inoculated into a YMA liquid culture medium at an inoculation rate of 1.5%, and cultured at 28°C for 5 days to obtain the Bradyrhizobium Qian2 agent.

[0013] Furthermore, the application amount of the carbon fixer is 5-10kg / mu.

[0014] The adjustment of the plant community structure specifically includes replanting potatoes and gramineous plants and reducing the number of dominant species of Asteraceae plants.

[0015] Furthermore, the leguminous plants include Lespedeza multiflora, Astragalus melilotifolia and Vicia fructus.

[0016] Furthermore, the grass plants include ophiopogon wilt, Cleistogenes squarrosa and Elymus dactylis.

[0017] Furthermore, the dominant species of Asteraceae plants are mainly Bidens pilosa, Artemisia ferulae and Artemisia capillaris.

[0018] Furthermore, the leguminous plants and the gramineous plants are mixed sown;

[0019] The sowing rates of Lespedeza multiflora, Astragalus melilotifolia, Vicia fructus, Herba Lycopodii, Cleistogenes squarrosa and Elymus dactylis are 0.835kg / mu, 0.415kg / mu, 0.415kg / mu, 0.25kg / mu, 0.25kg / mu and 0.335kg / mu respectively.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention applies a carbon fixer made of biochar, straw shreds and composite bacterial agents to the soil. On the one hand, the microbial nitrogen-fixing flora is reconstructed to increase soil carbon fixation while promoting soil nitrogen fixation and nitrification; and the improvement of soil microbial flora can improve the growth environment of plant roots and accelerate root development, thereby achieving the purpose of increasing underground soil carbon accumulation. On the other hand, porous biochar can absorb a large amount of carbon components, increase soil carbon storage capacity and increase carbon pool stability.

[0022] 2. As a pioneer species on the Loess Plateau, Asteraceae plants have evolved unique physiological and morphological characteristics in the process of adapting to drought and barrenness, such as scaly, strip-shaped, columnar or needle-shaped leaves that are conducive to water conservation. However, this also leads to low photosynthetic carbon fixation efficiency per unit leaf area of ​​Asteraceae plants, and their tall plants and developed root systems capture a large amount of light, heat, water and soil resources, affecting the photosynthetic carbon fixation of other short plants. The present invention reduces the niche width of dominant species of Asteraceae plants by reseeding leguminous and gramineous plants with higher carbon fixation efficiency, optimizes resource allocation, increases the amount of photosynthetic carbon fixation of plants, and thus promotes soil carbon accumulation;

[0023] 3. Allelopathic substances (such as terpenes, phenols, organic acid compounds, etc.) released by Asteraceae plants can inhibit the germination of seeds and the growth of seedlings of other herbaceous plants, and are prone to form a single community and reduce the stability of the ecosystem; the present invention can increase the aboveground vegetation coverage, plant diversity and species richness by reducing the number of dominant species of Asteraceae plants, reduce the risk of carbon loss caused by soil erosion, and play a role in conserving soil, water, fertilizer and carbon.

[0024] 4. The chrysanthemum family plants are usually inferior to the grass family and legume family in terms of feeding value. The potato family and grass family plants sown in the present invention have strong adaptability and high survival rate, which can increase the yield of forage grass with better palatability and improve the economic benefits of abandoned land;

[0025] 5. The method provided by the present invention can achieve the linkage effect of "plant photosynthetic carbon fixation - microorganisms promoting carbon with nitrogen - biochar carbon adsorption" by applying carbon fixers and adjusting the plant community structure, increase the combined above-ground and underground carbon fixation effects of abandoned land on the Loess Plateau, and synergistically improve the soil's carbon fixation capacity, carbon pool reserves and carbon pool stability. It is natural and environmentally friendly, highly operational, easy to implement and promote, and can quickly, effectively and continuously improve the soil's carbon fixation capacity. It is applicable to abandoned land on the Loess Plateau and other types of grassland. DETAILED DESCRIPTION

[0026] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0027] Example 1

[0028] This embodiment provides a method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau.

[0029] 1. Experimental Materials

[0030] 1. Source of Materials

[0031] The biochar used in the present invention is commercially available biochar;

[0032] The straw shreds used in the present invention are obtained by crushing commercially available straw;

[0033] The nitrobacter brevis vv6 was purchased from Guangdong Provincial Microbiological Culture Collection Center with a collection number of GDMCC NO: 60296; the nitrobacter XY-01 was purchased from the General Microbiological Center of China National Microbiological Culture Collection Committee with a collection number of CGMCC No. 10171; the self-generating nitrogen-fixing bacteria MBC5 was purchased from the General Microbiological Center of China National Microbiological Culture Collection Committee with a collection number of CGMCC No. 10821; the bradyrhizobium Qian2 was purchased from Guangdong Provincial Microbiological Culture Collection Center with a collection number of GDMCC NO: 61612.

[0034] 2. Culture medium preparation

[0035] Nitrobacillus brevis vv6 activation medium (LB liquid medium): 10 g of tryptone, 5 g of yeast extract, 10 g of sodium chloride, and 1000 mL of distilled water; LB solid medium requires an additional 18 g of agar;

[0036] Nitrobacter wilkeri XY-01 activation medium (HA liquid medium): 2.55 g sodium dihydrogen phosphate, 0.27 g potassium dihydrogen phosphate, 1.5 g sodium nitrite, 0.03 g magnesium sulfate, 0.01 g calcium chloride, 0.3 g sodium chloride, 0.03 g ferrous sulfate, 1000 mL distilled water; HA solid medium requires an additional 18 g agar.

[0037] Activated medium for spontaneous nitrogen-fixing bacteria MBC5 (GD liquid medium): 0.2 g potassium dihydrogen phosphate, 0.2 g magnesium sulfate, 0.2 g sodium chloride, 5 g calcium carbonate, 10 g mannitol, 0.1 g calcium sulfate, 1000 mL distilled water; GD solid medium requires an additional 20 g agar.

[0038] Bradyrhizobium Qian2 activated medium (YMA liquid medium): 0.5g potassium hydrogen phosphate, 0.2g sodium chloride, 0.2g magnesium sulfate heptahydrate, 0.1g calcium sulfate, 1g calcium carbonate, 0.001g vitamin B1, 0.001g vitamin B2, 100mL yeast juice, 10g mannitol, and distilled water to 1000mL; YMA solid medium requires an additional 18g agar.

[0039] 2. Preparation of soil carbon fixer

[0040] 1. Preparation of composite bacterial agent

[0041] (1) Preparation of Brevibacillus nitrificans vv6 bacterial agent

[0042] The strain vv6 was inoculated on LB solid culture medium for activation, and purified by 3-4 plate streaking transfers. The purified strain was inoculated into LB liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 4 days to obtain the nitrobacillus brevis vv6 inoculum.

[0043] (2) Preparation of Nitrobacter wilkeri XY-01 bacterial agent

[0044] The strain XY-01 was inoculated on HA solid culture medium for activation, and purified by 3-4 plate streaking transfers. The purified strain was inoculated into HA liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 3 days to obtain the Nitrobacter wilkeri XY-01 bacterial agent.

[0045] (3) Preparation of the autogenous nitrogen-fixing bacteria MBC5

[0046] The strain MBC5 was inoculated on GD solid culture medium for activation, and purified by transferring on solid plates 3-4 times. The purified strain was inoculated into GD liquid culture medium at an inoculation rate of 1.5%, and cultured at 28°C for 3 days to obtain the self-generating nitrogen-fixing bacteria MBC5 agent.

[0047] (4) Preparation of Bradyrhizobium Qian2 inoculant

[0048] The strain Qian2 was inoculated on YMA solid culture medium for activation, and purified by transferring on solid plates 3-4 times. The purified strain was inoculated into YMA liquid culture medium at an inoculation rate of 1.5%, and cultured at 28°C for 5 days to obtain Bradyrhizobium Qian2 agent.

[0049] The above-prepared Brevibacillus nitrifyingus vv6 agent, Nitrobacter vickers XY-01 agent, autogenous nitrogen-fixing bacteria MBC5 agent and Bradyrhizobium Qian2 agent were mixed in a volume ratio of 1:1:2:3 to obtain a composite agent; then the biochar, straw chips and the composite agent were evenly mixed in a dosage ratio of 5g:3g:10mL to obtain a soil carbon fixer.

[0050] 3. Experiment on improving soil carbon sequestration capacity in abandoned land on the Loess Plateau

[0051] 1. Overview of the pilot area

[0052] The experimental area is located in the Wuliwan Basin of Ansai District, Yan'an City, Shaanxi Province (36°51′~36°53′N, 109°20′~109°22′E), with an altitude of 1010~1400m, which is a typical loess hilly gully area. The area has a mid-temperate continental semi-arid monsoon climate, with an average temperature of 8.8℃, an annual average evapotranspiration of 1490mm, and an annual average rainfall of 505mm. Most of the rainfall is concentrated in July to September, accounting for about 70% of the annual rainfall. The average annual frost-free period is about 157d. The soil in the basin is mainly loess soil developed from aeolian loess parent material. The soil is loose, has poor erosion resistance, and suffers from serious soil and water loss. At present, there are 184.18hm2 of abandoned land in the Wuliwan Basin. 2 , which is the main land use type in the basin. Before the farmland was abandoned, it was mainly planted in rotation with corn (Zea mays) and millet (Setaria italica), with two crops per year; the farmland management was extensive, no fertilizer was applied, and irrigation mainly relied on rainfall. After the crops were harvested, all the above-ground parts were removed, and two tillages were carried out during the growing season, with a depth of 20cm. There was no human interference during the abandonment period, and the vegetation was naturally established and grew.

[0053] 2. Experimental Design

[0054] In 2001, the present invention selected a farmland abandoned in 1999 in the Wuliwan River Basin as a test site, with an area of ​​about 20m×20m. 12 plots were randomly established in the test site, each with an area of ​​4m×5m, and a distance of about 5m from each other. The plots were designed with randomized blocks, with group A being treated with carbon fixers, group B being treated with plant community structure adjustment, group AB being treated with the interaction of the two, and CK being the control group without any treatment; each treatment was repeated 3 times. Among them, the plots in group A (A1, A2, and A3) applied carbon fixers at a standard of 10kg / mu every year, and no other treatments were performed; the plots in group B (B1, B2, and B3) adjusted the plant community composition every 5 years, and no other treatments were performed; the plots in group AB (AB1, AB2, and AB3) applied carbon fixers at a standard of 10kg / mu every year, and adjusted the plant community composition every 5 years. All experiments started in 2002. Vegetation surveys are conducted in all plots every five years, and soil samples are collected to analyze changes in the carbon sequestration capacity of abandoned land.

[0055] 3. Vegetation survey methods

[0056] Vegetation survey was carried out in July, the peak season of vegetation growth. Five 1m×1m plots were set up in the four corners and the center of each plot for vegetation survey. The species names of all plants, the number of all plant species, the total number of each plant, and the coverage of each plant in each plot were recorded. The coverage was estimated by visual estimation. All survey work was completed by two investigators to reduce human errors, and all survey data were compiled into a book for subsequent analysis.

[0057] 4. Soil sample collection and carbon fixation capacity determination

[0058] In each plot, 10 sampling points were selected using the "S" type sampling method. After removing the surface litter and humus layer, a soil drill with an inner diameter of 5 cm was used to collect 0-10 cm surface soil samples. The 10 samples in the same plot were evenly mixed, sieved through a 2 mm sieve, put into a ziplock bag, and placed in a portable refrigerator for transport back to the laboratory. The soil samples were divided into two parts, one part was naturally air-dried, and the other part was stored at 4 ° C for subsequent analysis of soil carbon sequestration capacity. In addition, 3 soil profiles were randomly selected in each plot, using a volume of 100 cm 3 The circular knife was used to collect 0-10 cm original soil samples on the surface for determining soil bulk density.

[0059] Soil organic carbon stock (SOCs) and soil active organic carbon components and recalcitrant organic carbon components were selected to characterize the carbon sequestration capacity of soil. Among them, soil active organic carbon components include microbial biomass carbon (MBC), permanganate oxidative organic carbon (POXC) and particulate organic carbon (POC), which represent the physical, chemical and biological components of soil active organic carbon respectively; in addition, recalcitrant organic carbon components are represented by soil inert organic carbon (Recalcitrant organic carbon, ROC). The determination and calculation methods of the above indicators are described as follows.

[0060] The content of soil organic carbon (SOC) was determined by the potassium dichromate-concentrated sulfuric acid external calorimetric method. The soil bulk density was determined by the drying method, that is, the soil sample in the ring was placed at 105°C and dried to constant weight, and the weight of the dried soil per unit ring volume was weighed and calculated as the soil bulk density. The soil organic carbon stock was calculated according to the following formula:

[0061] SOC S =SOC×D×BD×K

[0062] In the formula, SOCs is the soil organic carbon storage (kg / m 2 ); SOC is soil organic carbon content (g / kg); D is soil thickness (cm); BD is soil bulk density (g / cm 3 ); K is a constant of 0.01.

[0063] The soil microbial biomass carbon (MBC) content was determined by chloroform fumigation extraction method. Weigh 20g of two soil samples stored at 4℃ and place them in a petri dish, one for chloroform fumigation and the other without fumigation. Put the fumigated soil in a desiccator with 5 beakers at the bottom, add 30mL of chloroform to each of the two beakers, add 30mL of distilled water to the other two beakers, and add 30mL of 0.5mol / L sodium hydroxide solution to the last beaker to absorb the CO2 released by the soil. Put the unfumigated soil sample in a desiccator with 3 beakers at the bottom, add 30mL of distilled water to each of the two beakers, and add 30mL of 0.5mol / L sodium hydroxide solution to the other one. After the desiccator is evacuated, place it in a 25℃ incubator for dark culture for 24h. After the incubation, 12.5 g of fumigated and unfumigated soil samples were weighed and placed in a 100 mL conical flask, 50 mL of 0.5 mol / L potassium sulfate solution was added, and then placed on a 25 ° C shaker for 30 min (200 rpm / min). After filtration, the carbon content in the solution was determined using a Shimadzu TOC instrument. The MBC content is the difference in carbon content between the fumigated and unfumigated soil samples.

[0064] The content of easily oxidizable organic carbon (POXC) in soil was determined by potassium permanganate oxidation colorimetry. Weigh 6-10g of air-dried soil sample (to ensure that the carbon content of each sample is within the range of 15-30mg) and place it in a 50mL centrifuge tube, and make a blank control (no soil sample). Add 25mL of 333mmol / L potassium permanganate solution, mix well and place it on a shaker at 25℃ for 1h (250rpm / min). After the end, centrifuge the centrifuge tube in a centrifuge at 4800rpm / min for 5 minutes, dilute the supernatant 1000 / 3 times with ultrapure water, and measure the absorbance of the dilution at 565nm with a spectrophotometer. 1mmol / L potassium permanganate consumes 9mg of carbon during the oxidation process. The amount of potassium permanganate consumed is calculated based on the difference in absorbance between the blank control and the sample solution, and then the POXC content is calculated.

[0065] The content of soil particulate organic carbon (POC) was determined by sodium hexametaphosphate extraction method. Weigh 20g of air-dried soil sample and place it in a 250mL conical flask, add 60mL of 5g / L sodium hexametaphosphate solution, shake it by hand for 10-15min, and then place it on a shaker for 18h (18℃, 90rpm / min). The dispersion was passed through a 53μm sieve and washed with ultrapure water until the water under the sieve was clear. The part above the sieve was particulate organic matter, which was placed at 80℃ for 24h for drying, weighed and calculated the percentage of particulate organic matter in the soil. The dried particulate organic matter was ground and passed through a 0.149mm sieve. A certain weight of particulate organic matter was taken and its carbon content was determined by the potassium dichromate-concentrated sulfuric acid external caloric method, and the POC content was calculated by multiplying it by the percentage of soil occupied.

[0066] The content of soil inert organic carbon (ROC) was determined by hydrochloric acid digestion. Weigh 2 g of air-dried soil sample that passed through a 1 mm sieve and place it in a 100 mL digestion tube, add 5 mL of 6 mol / L hydrochloric acid solution and digest it at 125 ° C for 16 hours. The digested soil sample was transferred to a 50 mL centrifuge tube, 30 mL of distilled water was added, shaken vigorously, and centrifuged in a centrifuge at 4000 rpm / min for 3 minutes. Pour out the supernatant, add 30 mL of distilled water again, and repeat the above steps 5 times until the hydrochloric acid is thoroughly washed out. After the washed soil sample is dried at 55 ° C, the ROC content is determined by the potassium dichromate-concentrated sulfuric acid external caloric method.

[0067] 5. Changes in plant community composition and soil carbon sequestration capacity in the control group (CK)

[0068] According to the above-mentioned vegetation survey method and soil index determination method, the plant community groups (Tables 1 and 2) and soil carbon sequestration capacity of the abandoned land in the control group changed between 2002 and 2022 (as shown in Table 3).

[0069] Table 1 Changes in plant community composition of abandoned land in the control group from 2002 to 2007

[0070]

[0071]

[0072]

[0073] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0074] Table 2 Changes in plant community composition of abandoned land in the control group from 2012 to 2022

[0075]

[0076]

[0077] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0078] Table 3 Changes in soil carbon sequestration capacity of abandoned land in the control group from 2002 to 2022

[0079]

[0080] Note: Data are mean ± standard error. Different lowercase letters in the same column indicate significant differences among different years (P<0.05).

[0081] The results shown in Tables 1 and 2 show that from 2002 to 2022, a total of 56 plant species were counted in the control group, belonging to 22 families, including 6 species of Gramineae, 4 species of Leguminosae, and 18 species of Asteraceae. On average, the density of Gramineae, Leguminosae, and Asteraceae plants was 11.80 plants / m 2 , 0.83 plants / m 2 and 21.38 strains / m 2 The coverage was 17.65%, 1.94% and 35.01% respectively. The density and coverage of Gramineae and Leguminosae increased during the trial period, but the increase of Gramineae was not obvious; although the increase of Leguminosae was huge, its overall density and coverage were not high.

[0082] The contribution of three Gramineae plants, namely, Aglaonema serrata, Elymus dahliae and Cleistogenes scabra, to the density and coverage of abandoned land plant communities increased year by year, from 0.48% (density contribution) and 1.11% (coverage contribution, the same below) in 2002 to 23.60% and 31.14% in 2022, respectively. Similarly, the contribution of three Leguminosae plants, namely, Vicia fruticosa, Astragalus melaleuca and Lespedeza multiflora, to the density and coverage of abandoned land plant communities also showed an increasing trend year by year, from 0% and 0% in 2002 to 2.89% and 5.47% in 2022, respectively. In addition, the contribution of three Asteraceae plants, namely, Bidens pilosa, Artemisia capillaris and Artemisia ferox, to the density and coverage of abandoned land plant communities were 22.02%-29.32% and 29.16%-47.66%, respectively, but there was no obvious interannual trend.

[0083] As shown in Table 3, from 2002 to 2022, the soil organic carbon reserves, microbial biomass carbon, easily oxidized organic carbon and particulate organic carbon contents increased year by year (P<0.05), with average increases of 29.55%, 75.90%, 253.33% and 57.82%, respectively; however, the soil inert organic carbon content did not change significantly, with an average increase of 13.80% during the experimental period. The above results generally indicate that the soil carbon sequestration capacity of the control group increased slowly.

[0084] 6. Experiment on improving soil carbon sequestration capacity of abandoned land

[0085] Starting from 2002, carbon fixers were applied on the soil surface of AB1, AB2 and AB3 plots at a rate of 10 kg / mu each year, and the plant community structure was adjusted in 2002, 2007, 2012, 2017 and 2022, respectively.

[0086] The specific implementation process of plant community structure adjustment is as follows:

[0087] (1) Reseeding of Leguminosae and Gramineae

[0088] This experiment selected the legumes Lespedeza multiflora, Astragalus melilotiformis, and Vicia oleracea as mixed with the Poaceae species Herba Lycopersicum, Cleistogenes scabra, and Elymus salsa. The sowing rate of each grass species in the mixed sowing combination is calculated by multiplying the mixed sowing ratio of the grass species in the mixed sowing combination by its single sowing rate. Among them, the single sowing rates of Lespedeza multiflora, Astragalus melilotiformis, Vicia oleracea, Herba Lycopersicum, Cleistogenes scabra, and Elymus salsa are 5.0kg / mu, 2.5kg / mu, 2.5kg / mu, 1.5kg / mu, 1.5kg / mu, and 2.0kg / mu, respectively. The legume-grass mixed sowing ratio (legume and Poaceae mixed sowing) is 1:1, and the total sowing rate is 2.5kg / mu. Therefore, when mixed sowing of beans and grass, the sowing rates of Lespedeza multiflora, Astragalus mellitus, Vicia fructus, Glechoma longituba, Cleistogenes squarrosa and Elymus ovata are 0.835kg / mu, 0.415kg / mu, 0.415kg / mu, 0.25kg / mu, 0.25kg / mu and 0.335kg / mu respectively.

[0089] The above six grass seeds were fully mixed and soaked in 45℃ warm water for 24h. After soaking, they were sown in rows. Each plot was sown 12 rows with a row spacing of 30cm and a sowing depth of 2cm. They were sown in 2002, 2007, 2012, 2017 and early April 2022. No fertilizer, irrigation or mowing was applied after sowing. Vegetation surveys were carried out at the end of July of the same year when vegetation was growing vigorously, and soil samples were collected to analyze soil carbon sequestration capacity.

[0090] The above-mentioned spatholobiaceae and cleistochete were purchased from Jiangsu Xinrui Seed Co., Ltd., the lycopodiella species, pea seeds and Lespedeza multiflora seeds were purchased from Jiangsu Gang Rinpoche Seed Co., Ltd., and the Astragalus melilotifolia seeds were provided by the Grassland Research Institute of the Academy of Agricultural and Animal Husbandry Sciences of Inner Mongolia Autonomous Region. All grass seeds had a germination rate of 73% to 89%, a water content of 3% to 12%, a purity of 80% to 90%, and a variety purity of 90% to 95%.

[0091] (2) Removal of dominant species of Asteraceae

[0092] To ensure the removal effect, the removal of dominant species of Asteraceae was completed one year before the reseeding of Leguminosae and Poaceae plants, that is, at the end of July in 2001, 2006, 2011, 2016 and 2021, respectively, all the Bidens pilosa, Artemisia annua and Artemisia capillaris in the experimental plot were removed by roots.

[0093] At the same time, for the experimental plots A1, A2 and A3, carbon fixation agents were applied at a rate of 10 kg / mu each year from 2002 to 2022, and the composition of the plant communities was not artificially changed; vegetation surveys were carried out at the end of July in 2002, 2007, 2012, 2017 and 2022, and soil samples were collected to analyze the soil carbon fixation capacity.

[0094] In addition, for the experimental plots B1, B2 and B3, the plant community structure was adjusted in early April in 2002, 2007, 2012, 2017 and 2022, respectively. The specific operations were as described above, but no carbon fixer was applied; vegetation surveys were carried out at the end of July in 2002, 2007, 2012, 2017 and 2022, respectively, and soil samples were collected to analyze the soil carbon fixation capacity.

[0095] 4. Experimental Results Analysis

[0096] 1. Effects of applying carbon fixers on soil carbon sequestration capacity of abandoned land on the Loess Plateau

[0097] After applying carbon fixation agents only, the composition of the aboveground plant community in abandoned land in 2002, 2007, 2012, 2017 and 2022 (Tables 4 and 5) and the carbon fixation capacity of the soil changed (as shown in Table 6).

[0098] Table 4 Changes in plant community composition in abandoned land treated with carbon fixation agents from 2002 to 2007

[0099]

[0100]

[0101]

[0102] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0103] Table 5 Changes in plant community composition of abandoned land treated with carbon fixation agents from 2012 to 2022

[0104]

[0105]

[0106]

[0107] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0108] As can be seen from Tables 4 and 5, from 2002 to 2022, a total of 62 plant species were counted in the plots where only carbon fixation agents were applied, belonging to 24 families; among them, there were 6 species of Gramineae, 5 species of Leguminosae, and 20 species of Asteraceae. On average, the density of Gramineae, Leguminosae, and Asteraceae plants was 12.23 plants / m 2 , 1.26 plants / m 2 and 22.23 strains / m 2, and the coverage was 20.17%, 2.20% and 33.08% respectively. Similar to the control group, the density and coverage of Gramineae and Leguminosae increased during the experiment, but the increase of Gramineae was not obvious; although the increase of Leguminosae was huge, its overall density and coverage were still not high. In general, the application of carbon fixers increased the species richness of the plant community in abandoned land, increased the density of Gramineae, Leguminosae and Compositae, increased the coverage of Gramineae and Leguminosae, but reduced the coverage of Compositae.

[0109] Specifically, after the application of carbon fixers, the contribution of three Poaceae plants, namely, Capillaris, Elymus dactylis and Cleistogenes serrata, to the density and coverage of abandoned land plant communities increased year by year, from 3.61% (density contribution) and 4.28% (coverage contribution, the same below) in 2002 to 23.84% and 31.87% in 2022, respectively; similarly, the contribution of three Leguminosae plants, namely, Vicia fragrans, Astragalus mellitus and Lespedeza multiflora, to the density and coverage of abandoned land plant communities also showed an increasing trend year by year, from 1.22% and 1.35% in 2002 to 4.39% and 4.24% in 2022, respectively. In addition, the contributions of three Asteraceae plants, Bidens pilosa, Artemisia capillaris and Artemisia argyi, to the density and coverage of abandoned land plant communities were 15.01%-36.33% and 17.56%-34.28%, respectively, and there was no obvious interannual change trend.

[0110] Compared with the control group, the application of carbon fixers increased the density of Gramineae, Leguminosae and Asteraceae by an average of 3.73%, 74.42% and 4.37%, respectively; and the density of the above three Gramineae, three Leguminosae and three Asteraceae was higher, with an average increase of 212.86%, 91.64% and 5.11% respectively compared with the control group. In addition, the application of carbon fixers increased the coverage of Gramineae and Leguminosae by an average of 17.31% and 104.31% respectively compared with the control group, but the coverage of Asteraceae decreased by 4.95% compared with the control group; similarly, after the application of carbon fixers, the coverage of the above three Gramineae and three Leguminosae increased by an average of 192.03% and 221.01% respectively compared with the control group, but the coverage of the three Asteraceae decreased by an average of 19.30% compared with the control group.

[0111] Table 6 Changes in soil carbon sequestration capacity of abandoned land treated with carbon sequestration agents from 2002 to 2022

[0112]

[0113] Note: Data are mean ± standard error. Different lowercase letters in the same column indicate significant differences among different years (P<0.05).

[0114] The results shown in Table 6 show that from 2002 to 2022, the soil organic carbon storage, microbial biomass carbon, easily oxidized organic carbon and particulate organic carbon content of the plot where only carbon fixers were applied increased year by year (P<0.05), with an average increase of 58.33%, 105.24%, 177.27% and 30.32%, respectively; the content of soil inert organic carbon did not change significantly, with an average increase of 21.64% during the experiment. In addition, compared with the control group, the application of carbon fixers increased the above five soil carbon fixation capacity indicators by 86.74%, 25.31%, 28.57%, 21.30% and 13.12% respectively, indicating that the application of carbon fixers alone can improve the carbon fixation capacity of abandoned land soil to a certain extent.

[0115] 2. Effects of adjusting plant community structure on soil carbon sequestration capacity of abandoned land on the Loess Plateau

[0116] After adjusting only the species composition of the plant community, the changes in the composition of the aboveground plant community and the carbon sequestration capacity of the soil in abandoned land in 2002, 2007, 2012, 2017 and 2022 are shown in Tables 7 and 8, respectively.

[0117] Table 7 Changes in plant community composition of abandoned land where only plant community structure was adjusted from 2002 to 2007

[0118]

[0119]

[0120]

[0121] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0122] Table 8 Changes in plant community composition of abandoned land with only plant community structure adjustment from 2012 to 2022

[0123]

[0124]

[0125] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0126] From Tables 7 and 8, we can see that from 2002 to 2022, a total of 55 species of plants belonging to 21 families were counted in the plots where only the plant community structure was adjusted; among them, there were 9 species of Gramineae, 6 species of Leguminosae, and 15 species of Asteraceae. On average, the density of Gramineae, Leguminosae, and Asteraceae plants was 16.47 plants / m 2 , 9.69 plants / m 2and 14.65 plants / m 2 , and the coverage was 35.84%, 20.83% and 17.69% respectively. Due to the regular adjustment of plant community composition, the density and coverage of Gramineae, Leguminosae and Asteraceae plants did not change much over time, but compared with the control group, the adjustment of plant community structure significantly improved the species evenness of the abandoned land plant community, increased the density and coverage of Gramineae and Leguminosae plants, and reduced the density and coverage of Asteraceae plants.

[0127] Specifically, after adjusting the plant community structure, the three Poaceae plants, namely, Capillaris, Elymus dactylis and Cleistogenes squarrosa, contributed 26.90%-28.90% and 35.17%-42.58% to the density and coverage of the abandoned land plant community, respectively; the three Leguminosae plants, namely, Vicia fructus, Astragalus mellitus and Lespedeza multiflora, contributed 16.03%-18.50% and 20.94%-28.02% to the density and coverage of the abandoned land plant community, respectively; the three Asteraceae plants, namely, Bidens pilosa, Artemisia capillaris and Artemisia scoparia, contributed 4.58%-12.06% and 2.89%-11.35% to the density and coverage of the abandoned land plant community, respectively; none of them showed obvious interannual change trends.

[0128] Compared with the control group, adjusting the plant community structure increased the density of Gramineae and Legume by an average of 40.43% and 1665.89%, respectively, and the density of the three Gramineae and Legume species mentioned above was even higher, with an average increase of 1778.85% and 1897.08% respectively compared with the control group. In addition, adjusting the plant community structure increased the coverage of Gramineae and Legume by an average of 125.95% and 2358.63% respectively compared with the control group, while the coverage of the three Gramineae and Legume species mentioned above increased by an average of 1920.01% and 5010.22% respectively compared with the control group. On the contrary, after adjusting the plant community structure, the density and coverage of Asteraceae decreased by an average of 30.38% and 48.89% respectively compared with the control group, especially the density and coverage of the three Asteraceae species decreased by an average of 64.47% and 76.55% respectively compared with the control group.

[0129] Table 9 Changes in soil carbon sequestration capacity of abandoned land with only plant community structure adjustment from 2002 to 2022

[0130]

[0131] Note: Data are mean ± standard error. Different lowercase letters in the same column indicate significant differences among different years (P<0.05).

[0132] As can be seen from Table 9, after adjusting the plant community structure, the average increase in soil organic carbon storage, microbial biomass carbon, easily oxidized organic carbon, particulate organic carbon and inert organic carbon content from 2002 to 2022 was 20.69%, 115.31%, 211.11%, 108.97% and 9.52%, respectively; although the various indicators characterizing the soil carbon sequestration capacity generally showed an increasing trend over time, the differences in soil organic carbon storage and inert organic carbon content between different years did not reach a significant level. In addition, adjusting the plant community structure increased the soil organic carbon storage, microbial biomass carbon, easily oxidized organic carbon and inert organic carbon content by 25.89%, 6.88%, 14.00% and 2.16% respectively compared with the control group, but the soil particulate organic carbon content decreased by 28.44% compared with the control group; the above results show that only adjusting the plant community structure can also improve the carbon sequestration capacity of abandoned land soil to a certain extent, but its effect is lower than that of applying carbon fixers alone.

[0133] 3. Impact of the present invention on soil carbon sequestration capacity of abandoned land on the Loess Plateau

[0134] After applying carbon fixation agents and adjusting the plant community structure, the changes in the composition of the aboveground plant community and the carbon fixation capacity of the soil in abandoned land in 2002, 2007, 2012, 2017 and 2022 are shown in Tables 10 and 11, respectively.

[0135] Table 10 Changes in plant community composition of abandoned land implementing the present invention from 2002 to 2007

[0136]

[0137]

[0138] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0139] Table 11 Changes in plant community composition of abandoned land implementing the present invention from 2012 to 2022

[0140]

[0141]

[0142] Note: Data are mean ± standard error. “-” means that there is no such plant species in the abandoned land in the corresponding year.

[0143] From Tables 10 and 11, it can be seen that from 2002 to 2022, a total of 59 species of plants belonging to 23 families were counted in the plots implementing the present invention; among them, there were 10 species of Gramineae, 9 species of Leguminosae, and 15 species of Asteraceae. On average, the density of Gramineae, Leguminosae, and Asteraceae plants was 17.10 plants / m 2 , 9.78 plants / m 2 and 13.47 strains / m 2 , and the coverage was 35.40%, 20.66% and 19.16% respectively. After the implementation of the present invention, the density and coverage of Gramineae, Leguminosae and Asteraceae plants were not much different from those of the plots where only the plant community structure was adjusted, but compared with the control group and the plots where only the carbon fixer was applied, the implementation of the present invention significantly improved the species uniformity of the abandoned land plant community, increased the density and coverage of Gramineae and Leguminosae plants, and reduced the density and coverage of Asteraceae plants.

[0144] Specifically, after the implementation of the present invention, the three Gramineae plants, namely, Capillaris, Elymus dactylis and Cleistogenes squarrosa, contributed 24.29%-34.16% and 32.97%-41.85% to the density and coverage of the abandoned land plant community, respectively; the three Leguminosae plants, namely, Vicia oleraceus, Astragalus melilotus and Lespedeza multiflora, contributed 16.00%-18.94% and 14.93%-25.91% to the density and coverage of the abandoned land plant community, respectively; the three Asteraceae plants, namely, Bidens pilosa, Artemisia capillaris and Artemisia scoparia, contributed 3.13%-10.93% and 2.22%-6.22% to the density and coverage of the abandoned land plant community, respectively; none of them showed obvious interannual variation trends.

[0145] Compared with the control group, the implementation of the present invention increases the density of Gramineae and Legumes by an average of 45.70% and 1672.06%, respectively, and the density of the above three Gramineae and Legumes is increased by an average of 1895.93% and 2000.47% respectively compared with the control group; in addition, the implementation of the present invention increases the coverage of Gramineae and Legumes by an average of 122.72% and 2465.90% respectively compared with the control group, and the coverage of the above three Gramineae and Legumes is 1859.14% and 6167.90% higher than the control group. On the contrary, the density and coverage of Asteraceae are reduced by an average of 36.04% and 44.87% respectively compared with the control group, and the density and coverage of the above three Asteraceae are reduced by an even lower amount, which are reduced by an average of 70.46% and 86.07% respectively compared with the control group.

[0146] Table 12 Changes in soil carbon sequestration capacity of abandoned land implementing the present invention from 2002 to 2022

[0147]

[0148]

[0149] Note: Data are mean ± standard error. Different lowercase letters in the same column indicate significant differences among different years (P<0.05).

[0150] As can be seen from Table 12, applying carbon fixers and adjusting the plant community structure can significantly improve the soil carbon fixation capacity of abandoned land. The average increases in soil organic carbon reserves, microbial biomass carbon, easily oxidized organic carbon, particulate organic carbon and inert organic carbon content between 2002 and 2022 were 66.67%, 148.00%, 169.23%, 77.48% and 34.81% (P<0.05), respectively. Compared with the control group, the implementation of the present invention increased the above five indicators characterizing soil carbon fixation capacity by an average of 153.38%, 47.45%, 51.93%, 17.39% and 17.85% respectively compared with the control group. By comparing the results between different treatments, it can be seen that the present invention has the best effect on improving soil carbon fixation capacity.

[0151] 4. Comparison of the effects of different treatments on improving soil carbon sequestration capacity of abandoned land

[0152] Table 13 Comparison of soil carbon sequestration enhancement effects of different treatments compared with the control group from 2002 to 2022

[0153]

[0154]

[0155] Note: Data are mean ± standard error.

[0156] Table 13 shows the increment of soil carbon sequestration capacity of abandoned land in 2002, 2007, 2012, 2017 and 2022 compared with the control group after only applying carbon sequestration agent, only adjusting plant community structure and implementing the present invention. It can be seen that:

[0157] (1) Except for a few exceptional scenarios, applying carbon fixers alone and adjusting plant community structure alone can also improve soil carbon fixation capacity, but the effect is significantly lower than the improvement effect of implementing the present invention; specifically, the improvement effect of the present invention on soil organic carbon storage, microbial biomass carbon content, easily oxidizable organic carbon content and inert organic carbon content is 1.77 times, 1.80 times, 1.79 times and 1.35 times, respectively, of the effect of applying carbon fixers alone, and 5.84 times, 5.39 times, 2.75 times and 6.02 times, respectively, of the effect of adjusting plant community structure alone.

[0158] (2) During the period 2002-2022, the implementation of the present invention can increase soil organic carbon reserves, microbial biomass carbon content, easily oxidizable organic carbon content, particulate organic carbon content and inert organic carbon content by an average of 152.84%, 49.98%, 67.96%, 18.00% and 19.45%, respectively; in particular, the above five indicators can be increased by 126.67%, 13.70%, 82.91%, 3.10% and 10.57%, respectively, in the year of the implementation of the present invention, and the improvement effect shows an overall increasing trend year by year, indicating that the present invention can quickly, effectively and continuously improve the carbon sequestration capacity of abandoned land soil on the Loess Plateau and can be promoted and applied.

[0159] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0160] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau, characterized in that: Apply carbon fixers to the soil and adjust plant community structure; The carbon fixer is prepared from biochar, straw shreds and composite bacterial agent in a dosage ratio of 4-6 g: 2-3 g: 6-10 mL; The composite bacterial agent is prepared by mixing Brevibacillus nitrificans vv6, Nitrobacter veseri XY-01, autogenous nitrogen-fixing bacteria MBC5 and Bradyrhizobium Qian2 in a volume ratio of 1:1:2-3:2-4. The adjustment of the plant community structure specifically includes reseeding leguminous plants and gramineous plants and reducing the number of dominant species of Asteraceae plants.

2. The method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 1, characterized in that: The preparation process of the nitrifying Bacillus vv6 bacterial agent is as follows: the strain vv6 is inoculated on an LB solid culture medium for activation, purified by 3-4 plate streaking transfers, the purified strain is inoculated into an LB liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 4 days to obtain the nitrifying Bacillus vv6 bacterial agent.

3. A method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 2, characterized in that: The preparation process of the Nitrobacter vickers XY-01 bacterial agent is as follows: the strain XY-01 is inoculated on a HA solid culture medium for activation, purified by 3-4 plate streaking transfers, the purified strain is inoculated into a HA liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 3 days to obtain the Nitrobacter vickers XY-01 bacterial agent.

4. A method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 3, characterized in that: The preparation process of the self-generated nitrogen-fixing bacteria MBC5 agent is as follows: the strain MBC5 is inoculated on a GD solid culture medium for activation, purified by transferring on a solid plate 3-4 times, the purified strain is inoculated into a GD liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 3 days to obtain the self-generated nitrogen-fixing bacteria MBC5 agent.

5. A method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 4, characterized in that: The preparation process of the bradyrhizobium Qian2 agent is as follows: the strain Qian2 is inoculated on a YMA solid culture medium for activation, purified by transferring on a solid plate 3-4 times, inoculated into a YMA liquid culture medium at an inoculation rate of 1.5%, and cultured at 28° C. for 5 days to obtain the bradyrhizobium Qian2 agent.

6. The method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 1, characterized in that: The application amount of the carbon fixer is 5-10kg / mu.

7. The method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 1, characterized in that: The leguminous plants include Lespedeza multiflora, Astragalus melilotus and Vicia fructus.

8. The method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 7, characterized in that: The grasses include ophiopogon wilt, Cleistogenes squarrosa and Elymus salsa.

9. The method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 8, characterized in that: The dominant species of Asteraceae plants are mainly Bidens pilosa, Artemisia ferulae and Artemisia capillaris.

10. The method for improving the carbon sequestration capacity of abandoned land in the Loess Plateau according to claim 9, characterized in that: The legumes and gramineous plants are mixed sown; the sowing rates of Lespedeza multiflora, Astragalus melilotus, Vicia fruticosa, Herba Lysimachiae, Cleistogenes squarrosa and Elymus dactylis are 0.835kg / mu, 0.415kg / mu, 0.415kg / mu, 0.25kg / mu, 0.25kg / mu and 0.335kg / mu respectively.

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