Multi-layer mesh bag for restoring soil molybdenum pollution based on arbuscular mycorrhizal fungi and manufacturing method and application thereof

Abstract

The invention relates to a multi-layer mesh bag for restoring soil molybdenum pollution based on arbuscular mycorrhizal fungi and a manufacturing method and application thereof.The multi-layer mesh bag is of an integrated structure with the top open and the bottom closed, and the mesh bag is sequentially filled with a water retention nutrition layer material, a heavy metal passivation layer material and a core strain layer material from outside to inside; the material of the water-retaining nutrition layer is formed by mixing reed straw, vermiculite and decomposed sheep manure according to the mass ratio of 3: 2: 2; the heavy metal passivation layer material is formed by mixing attapulgite, ground phosphate rock and potassium humate according to the mass ratio of 3: 2: 1; the material of the core strain layer is a mixed system of an arbuscular mycorrhizal inoculant-turfy soil mixture and a polyvinyl alcohol water melt bag filled with seeds. By optimizing the mesh bag layered structure and screening the efficient symbiotic system, rapid improvement and vegetation reconstruction of molybdenum tailing soil are achieved, and the problems that in an existing molybdenum tailing remediation technology, the microorganism planting rate is low, the plant survival rate is poor, and the remediation efficiency is low are solved.

Description

Technical Field

[0001] This invention belongs to the field of soil heavy metal pollution remediation technology, specifically relating to a multi-layer mesh bag for remediating soil molybdenum pollution based on arbuscular mycorrhizal fungi, its manufacturing method, and its application. Background Technology

[0003] Currently, the main technologies for remediating molybdenum tailings soil include physical leaching, chemical passivation, and bioremediation. Physical leaching consumes a large amount of water and is prone to secondary pollution. While chemical passivation can reduce molybdenum availability in the short term, it has poor long-term stability and can damage the original soil structure. In contrast, bioremediation has become a research hotspot due to its environmental friendliness and low cost, with microbial-plant co-remediation technology being widely used. However, in existing microbial-plant co-remediation technologies, commonly used amendments are mostly based on single organic materials such as straw and livestock manure. Although these can improve fertility to some extent, they have drawbacks such as slow nutrient release, potential introduction of heavy metals or antibiotics, and insufficient adaptability to high-molybdenum environments, and their improvement effect cannot fully meet the requirements. Furthermore, in the construction of microbial-plant synergistic remediation systems, research has focused on the combination of growth-promoting bacteria, decomposing microorganisms, and plants, while the application of highly efficient symbiotic remediation combinations of arbuscular mycorrhizal fungi and molybdenum-tolerant plants is still in the exploratory stage. Technical details such as microbial colonization enhancement and synergistic nutrient supply in molybdenum tailings soil still need to be improved.

[0004] Regarding plant selection, some herbaceous plants currently used in molybdenum tailings remediation have limited capacity for molybdenum enrichment and translocation, and their symbiotic compatibility with remediation-functional microorganisms needs improvement. Furthermore, existing remediation technologies often involve simple mixing of amendments, microorganisms, and plants, resulting in low microbial colonization rates, unbalanced nutrient supply, and low plant survival rates. This leads to long remediation cycles and makes it difficult to meet the needs of large-scale remediation. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a multi-layered mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi, along with its manufacturing method and application. By optimizing the layered structure of the mesh bag and screening for highly efficient symbiotic systems, it achieves rapid improvement and vegetation reconstruction of molybdenum tailings soil, thereby solving problems such as low microbial colonization rate, poor plant survival rate, and low remediation efficiency in existing molybdenum tailings remediation technologies.

[0006] The present invention is specifically achieved through the following technical solution: According to the present invention, a multi-layer mesh bag for remediating soil molybdenum pollution based on arbuscular mycorrhizal fungi is proposed. The mesh bag is an integrated structure with an open top and a sealed bottom. The mesh bag is filled with water-retaining nutrient layer material, heavy metal passivation layer material and core fungal layer material from the outside to the inside. The water-retaining nutrient layer material is composed of reed straw, vermiculite, and well-rotted sheep manure in a mass ratio of 3:2:2. The reed straw is rich in cellulose and hemicellulose, which can slowly degrade in the soil, continuously providing a carbon source. Vermiculite has a layered structure and a water retention rate of 4-6 times its own weight, effectively intercepting rainwater or irrigation water and alleviating the problem of poor water retention in molybdenum tailings soil. The well-rotted sheep manure contains ≥40% organic matter, ≥5% total nitrogen, phosphorus, and potassium, and is rich in trace elements, which can slowly release nutrients through microbial degradation. Simultaneously, as the outer structure of the mesh bag, the water-retaining nutrient layer buffers the impact of the external environment on the internal system, preventing seed germination and seedling growth from being affected by extreme temperatures. The heavy metal passivation layer material is composed of attapulgite, phosphate rock powder, and potassium humate mixed in a mass ratio of 3:2:1; the specific surface area of ​​the attapulgite is ≥300 m². 2 / g, has a strong adsorption capacity and can fix molybdenum ions through physical adsorption; phosphate ions in phosphate rock powder can form molybdenum phosphate precipitate with molybdenum ions, which significantly reduces the content of soluble molybdenum in the soil; potassium humate has a humic acid content of ≥55%, which can promote the formation of soil aggregate structure and improve the soil's fertilizer retention capacity. Its carboxyl, hydroxyl and other functional groups can form complexes with molybdenum ions, which can help reduce the availability of heavy metals, while providing a favorable microenvironment for the subsequent germination of microorganisms; The core inoculum layer material is a mixture of dried arbuscular mycorrhizal fungi inoculum and peat moss, combined with seed-filled polyvinyl alcohol (PVA) water-soluble bags. The seed-filled PVA water-soluble bags are placed in the center of the arbuscular mycorrhizal fungi inoculum-peat moss mixture. The preparation method of the core inoculum layer material includes: first, preparing the arbuscular mycorrhizal fungi inoculum-peat moss mixture by mixing the fungi and peat moss at a mass ratio of 1:5; second, individually packaging the seeds by placing 10-15 seeds into a seed-specific PVA water-soluble bag; and finally, mixing the seed-filled PVA water-soluble bag into the fungi inoculum-peat moss mixture to form the core inoculum layer. This core inoculum layer is in a dry state, which ensures the activity of the fungal spores and the quality of seed preservation, extending the storage time in the mesh bag.

[0007] Free molybdenum ions in molybdenum-contaminated soil are biotoxic and inhibit the hyphal germination and growth of arbuscular mycorrhizal fungi. This invention utilizes a multi-layered mesh bag for remediating molybdenum-contaminated soil using arbuscular mycorrhizal fungi. During use, the outer water-retaining and nutrient-rich layer first adsorbs some of the free molybdenum ions in the soil, while the middle heavy metal passivation layer effectively immobilizes the molybdenum ions that penetrate the outer layer, preventing high-concentration molybdenum ions from directly contacting the core fungal layer located in the inner layer, thereby ensuring the activity and colonization ability of the arbuscular mycorrhizal fungi.

[0008] The aforementioned multi-layered mesh bags for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi are woven from biodegradable flax fibers. As a natural plant fiber, flax fibers gradually decompose into loose organic debris during degradation, breaking up soil compaction, increasing soil porosity, and improving soil aeration and water permeability, which is beneficial for plant root respiration and extension. Flax fibers themselves contain elements such as carbon, hydrogen, and oxygen, which are decomposed into organic matter by soil microorganisms during degradation. This not only enhances the soil's ability to retain fertilizer and water but also provides a small amount of nutrients for soil microorganisms and plant growth. The fiber degradation process provides a nutrient source for beneficial microorganisms in the soil, promoting microbial reproduction, making the soil microbial community more active, and thus improving the soil's microbial activity and nutrient conversion capacity.

[0009] The aforementioned multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi comprises reed straw with a particle size of 1-2 cm, vermiculite with a particle size of 2-5 cm, and attapulgite soil with a specific surface area ≥300 m². 2 / g, potassium humate with humic acid content ≥55%; arbuscular mycorrhizal fungi agent and peat moss are mixed evenly at a mass ratio of 1:5, wherein the arbuscular mycorrhizal fungi agent is *Tectus mosierifolia*, with a spore content ≥50 / g; the *Tectus mosierifolia* ( Funneliformis mosseae It exhibits strong tolerance to molybdenum stress and good symbiotic relationship with various herbaceous plants. The peat soil has an organic matter content of ≥70% and a pH value of 5.5-6.5, providing a suitable microenvironment for the growth of arbuscular mycorrhizal fungi and promoting their spore germination and mycelial growth. Each polyvinyl alcohol water-soluble bag contains 10-15 seeds. The seed-specific polyvinyl alcohol water-soluble bag is made of water-soluble polyvinyl alcohol film with a thickness of 0.03-0.05mm. It can completely dissolve in water at ≥10℃ for 3-5 minutes without leaving any harmful substances. The film can be stably stored for more than 12 months under dry storage conditions (relative humidity ≤40%). It can automatically dissolve and release seeds upon contact with water, eliminating the need for seedling cultivation and transplanting, and allowing for direct planting.

[0010] The aforementioned multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi uses symbiotic plant seeds. These symbiotic plants must meet the following characteristics: (a) they have a strong capacity for molybdenum enrichment and translocation, efficiently absorbing molybdenum from the soil and transferring it to the aboveground parts; (b) they have a high degree of symbiotic compatibility with arbuscular mycorrhizal fungi, forming a stable symbiotic system to enhance stress resistance; (c) they have strong stress tolerance, growing normally in molybdenum tailings soils with low nutrients and high molybdenum stress; and (d) they have a short growth cycle and rapid biomass accumulation, facilitating the removal of heavy metals and resource recycling through harvesting.

[0011] Preferably, the seeds are selected from herbaceous leguminous plants. Herbaceous leguminous plants generally have well-developed fibrous root systems, which can quickly adapt to the loose structure of molybdenum tailings soil and expand the range of nutrient and heavy metal absorption. Their root systems can form an efficient symbiotic system with arbuscular mycorrhizal fungi, and enhance nutrient absorption and heavy metal passivation capabilities through the fungal hyphal network. The root nodules of some varieties can also fix atmospheric nitrogen and improve soil nitrogen nutrition. At the same time, herbaceous leguminous plants have short growth cycles, strong reproductive capabilities, and rapid biomass accumulation, making it easy to quickly remove the enriched molybdenum through harvesting, thus possessing both ecological restoration and soil fertility enhancement value.

[0012] More preferably, the seeds are selected from alfalfa ( Medicago sativa Alfalfa seeds possess the following characteristics: (a) outstanding molybdenum enrichment capacity, enabling efficient absorption and translocation of molybdenum; (b) good symbiosis with *Glomus mosyensis*, with root mycorrhizal infection rate reaching over 85% after 4 weeks of inoculation, and the fresh weight of plant roots increasing by over 60% after symbiosis, significantly enhancing stress resistance; (c) strong stress tolerance, able to grow normally under pH 4.5-8.5 and drought stress conditions, with a germination rate ≥90% in molybdenum tailings soil; (d) a perennial herbaceous plant, which can be harvested continuously for 3-5 years after a single planting, with 2-3 harvests per year, eliminating the need for repeated planting and reducing long-term remediation costs; (e) a growth cycle of 90-100 days per crop, with a plant height of 60-80cm, and a large aboveground biomass, facilitating the continuous removal of molybdenum ions from the soil through multiple harvests, resulting in stable and long-lasting remediation efficiency.

[0013] Furthermore, besides alfalfa, other herbaceous legumes suitable for molybdenum pollution remediation include: (1) White clover ( Trifolium repens It is a perennial creeping herbaceous plant with good molybdenum accumulation capacity and strong molybdenum stress resistance. After planting, it can quickly cover the ground surface, suppress dust and reduce soil erosion. Moreover, one planting can be used continuously for 3-5 years without frequent replanting, thus balancing the restoration effect and cost control. (2) Arrowhead peas ( Vicia sativa It is an annual herbaceous plant with the advantages of a short growth cycle, which can quickly complete a remediation cycle. The planting density and frequency can be flexibly adjusted according to the soil molybdenum pollution concentration, making it highly targeted for remediation. It has excellent molybdenum transfer ability, high seed germination rate, drought and barren soil tolerance, and wide adaptability, making it suitable for large-scale rapid sowing and remediation. It also has a well-developed root system and strong nitrogen fixation ability. After green manure application, it can significantly increase soil organic matter, improve soil physical and chemical properties, and simultaneously enhance soil fertility. The disadvantage is that it needs to be replanted every year, and long-term application will increase planting and labor costs. (3), milkvetch ( Astragalus sinicusThis is an annual herbaceous plant. Its core advantage is its strong adaptability to acidic molybdenum tailings soil, enabling it to thrive in acidic polluted soils where perennial plants struggle to survive. Its root exudates can reduce soil molybdenum availability and decrease molybdenum migration to deeper soil layers, resulting in good molybdenum accumulation capacity. It also exhibits outstanding nitrogen-fixing ability, rapidly increasing soil nitrogen content and laying the foundation for subsequent vegetation reconstruction. Its seeds are widely available and easy to sow, allowing it to be mixed with other remediation plants to form a composite remediation system, enhancing overall remediation stability. However, it also requires annual sowing, leading to relatively high labor and seed costs for long-term remediation.

[0014] The following is a comparison of the preferred seed categories and their plant characteristics: Table 1. Comparison of preferred seed categories and their plant characteristics In one embodiment, the mesh bag has a diameter of 20cm, a height of 15cm, and a mesh opening diameter of 0.5-1cm, which ensures water penetration and root extension while preventing the mixing of materials from different layers.

[0015] In one embodiment, the thickness of the water-retaining nutrient layer is 3 cm, the thickness of the heavy metal passivation layer is 3 cm, and the diameter of the core bacterial layer is 8 cm.

[0016] This invention also provides a method for manufacturing the aforementioned multi-layer mesh bag for remediating molybdenum contamination in soil based on arbuscular mycorrhizal fungi. Taking a mesh bag with a diameter of 20 cm and a height of 15 cm as an example, the method specifically includes: Step (1): Making the mesh bag skeleton: Use flax fiber to weave a cylindrical mesh bag with a diameter of 20cm and a height of 15cm. The mesh size of the mesh bag is 0.5-1cm. The bottom of the mesh bag is sewn with a round flax cloth to prevent material leakage and ensure that the mesh bag is an integrated structure with an open top and a sealed bottom. Step (2): Layered filling material: An integrated concentric three-layer ring structure plastic mold is used to assist in positioning and filling. The integrated concentric three-layer ring structure plastic mold includes an outer cylindrical ring (radial width 3cm), a middle cylindrical ring (radial width 3cm) and a central cylindrical ring (diameter 8cm). The central cylindrical ring is a hollow structure. The overall outer diameter of the integrated concentric three-layer ring structure plastic mold is 20cm, which is precisely matched with the inner diameter of the mesh bag. The specific filling process is as follows: The integrated concentric three-layer ring structure plastic mold is placed inside the mesh bag, with the outer cylindrical ring fitting tightly against the inner wall of the mesh bag, and the bottom of the mold fitting tightly against the bottom of the mesh bag; the cavity between the outer and middle cylindrical rings serves as the filling space for the water-retaining nutrient layer, the cavity between the middle and central cylindrical rings serves as the filling space for the heavy metal passivation layer, and the inner cavity of the central cylindrical ring serves as the filling space for the core bacterial layer; the water-retaining nutrient layer material is poured into the cavity between the outer and middle cylindrical rings. Use a pressure plate to gently compact the material until the water-retaining nutrient layer is flush with the top of the outer cylindrical ring. Pour the heavy metal passivation layer material into the cavity between the middle and central cylindrical rings, and gently compact it until it is flush with the top of the middle cylindrical ring. Pour the dry core microbial layer material into the cavity inside the central cylindrical ring, and gently spread it so that it is flush with the top of the central cylindrical ring. No compaction is required. Finally, slowly and vertically remove the integrated concentric three-layer ring structure plastic mold from the top of the mesh bag to complete the layered filling. Step (3): Dry storage: Place the prepared mesh bag in a dry and ventilated environment for storage. The storage conditions are: temperature 15-25℃, relative humidity ≤40%, avoid direct sunlight. Under these conditions, it can be stored stably for 10-12 months and can be taken out as needed.

[0017] Furthermore, the integrated concentric three-layer ring structure plastic mold includes an outer cylindrical ring component, a middle cylindrical ring component, and a central cylindrical ring component. The central cylindrical ring component is a hollow structure. The outer cylindrical ring component, the middle cylindrical ring component, and the central cylindrical ring component are connected into an integrated structure by a connecting plate. The connecting plate is arranged radially along the outer cylindrical ring component, with one end connected to the outer wall of the central cylindrical ring component and the other end connected to the inner wall of the outer cylindrical ring component. The connecting plate is also connected to the middle cylindrical ring component, so that the outer cylindrical ring component, the middle cylindrical ring component, the central cylindrical ring component, and the connecting plate form an integrated mold structure.

[0018] This invention also provides an application of a multi-layer mesh bag based on arbuscular mycorrhizal fungi for the remediation of molybdenum contaminated soil in molybdenum tailings soil pollution. Taking a mesh bag with a diameter of 20 cm as an example, the application method specifically includes the following steps: (1) Site pretreatment: Clean up large gravel and impurities in the molybdenum tailings area to be repaired, plow the tailings sand to 20-30cm, level the land and mark the planting points with a row spacing of 30cm and a plant spacing of 20cm. (2) Planting in pits: Dig planting pits with a diameter of 22cm and a depth of 15cm at the planting point. The depth and diameter of the planting pits should be matched with the size of the multi-layer mesh bags for remediating molybdenum pollution in the soil, and allow space for backfilling. Place the stored multi-layer mesh bags for remediating molybdenum pollution in the soil directly into the planting pits, ensuring that the top of the mesh bags is flush with the ground surface. Then backfill and compact the surrounding tailings soil to prevent the mesh bags from shaking. (3) Irrigation activation: Water immediately after planting to activate the fungus. The amount of water for each planting point is 500-800 mL. Ensure that the materials in each layer of the net bag are fully moistened. The polyvinyl alcohol water-soluble bag containing seeds in the core fungal layer dissolves when it comes into contact with water, releasing the seeds and activating the germination of arbuscular mycorrhizal fungal spores. Afterward, maintain the soil moisture content at 18-25% and drain water in time during the rainy season to prevent waterlogging. (4) Harvesting and recycling: After the seed plants have grown for 90-100 days, use a harvester to harvest the above-ground parts at a height of 5-8cm from the ground surface. Transport the harvested plants to a professional treatment plant for incineration and recover molybdenum resources from the ash. After harvesting, apply 100g of well-rotted sheep manure per plant to promote regeneration.

[0019] Preferably, in the above application method, the remediation cycle is 2-3 years, and 3-4 crops of aboveground parts of the plants can be harvested each year. The monitoring indicators include: (1) Soil indicators: Collect soil samples from the 0-20cm layer around the net bag every quarter to test the soil molybdenum content, organic matter content, pH value and the proportion of aggregate structure (>0.25mm); (2) Plant indicators: Measure plant height, fresh biomass and aboveground molybdenum content at each harvest; (3) Microbial indicators: Measure the root mycorrhizal infection rate and the density of arbuscular mycorrhizal fungal spores in the soil every six months. When the soil molybdenum content is ≤100mg / kg, the organic matter content is ≥2%, and the proportion of aggregate structure is ≥15%, the remediation is deemed to have met the standards.

[0020] Compared with existing technologies, this invention has significant advantages and beneficial effects. Through the above technical solution, this invention achieves considerable technological advancement and practicality, and has broad application value, possessing at least the following advantages: (1) Significantly improved remediation efficiency and simple operation: This invention achieves an integrated synergistic effect of "water retention and fertilization - molybdenum ion passivation - combined activation of fungal agent and seeds" through the three-layer structure design of the mesh bag. The fungal agent and seeds in the core fungal layer are directly mixed and matched, which can advance the symbiotic start time of arbuscular mycorrhizal fungi and plant roots by about 2-3 weeks, and increase the root mycorrhizal infection rate to more than 85%. The use of seed-specific polyvinyl alcohol water-soluble bags to replace traditional seedling transplanting eliminates the seedling stage and improves planting efficiency. The plant germination rate is increased to more than 90%, the remediation cycle is shortened to 2-3 years, and the soil molybdenum content can be stably reduced to below 100mg / kg after remediation.

[0021] (2) Continuous improvement of soil quality: The water-retaining nutrient layer of the present invention can continuously release nutrients, which significantly increases the soil organic matter content; the synergistic effect of the heavy metal passivation layer and arbuscular mycorrhizal fungi significantly reduces the soluble molybdenum content in the soil; the vermiculite in the water-retaining nutrient layer increases the soil water retention rate from less than 10% to more than 20%, which significantly improves the physical and chemical properties of molybdenum tailings soil.

[0022] (3) Good storage and low cost: The core microbial layer is in a dry state, and combined with the breathable properties of the biodegradable flax fiber mesh bag, it can be stored for 10-12 months under dry conditions, which is convenient for large-scale storage and cross-regional transportation. The materials of each layer are agricultural waste (reed stalks, sheep manure, etc.) or natural minerals, which are widely available and eliminate the seedling stage, further reducing labor costs. After the plants are harvested, molybdenum resources can be recovered, realizing the dual benefits of remediation and resource recovery, and further reducing remediation costs.

[0023] (4) Environmentally friendly and free from secondary pollution: The mesh bag is made of biodegradable flax fiber, which can be completely degraded into organic matter in 6-12 months without secondary pollution; the polyvinyl alcohol film used for seed packaging can be completely dissolved without residue, and all filling materials are natural and environmentally friendly materials. The entire remediation process has no negative impact on the environment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the multi-layer mesh bag for remediating molybdenum pollution in soil based on arbuscular mycorrhizal fungi, as described in this invention.

[0025] Figure 2 This is a schematic diagram of a one-piece concentric three-layer ring structure plastic mold.

[0026] In the diagram, 1-water-retaining nutrient layer, 2-heavy metal passivation layer, 3-core microbial culture layer, 4-outer cylindrical ring component, 5-middle cylindrical ring component, 6-central cylindrical ring component, 7-connecting plate. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all conditions in the following examples were performed under standard conditions or conditions recommended by the manufacturer. Raw materials and reagents whose manufacturers are not specified were all commercially available products. The following examples used *Tetranychus mossae* (a type of fungus). Funneliformis mosseaeProvided by China Agricultural University, it has been deposited in the Germplasm Bank of Arbuscular Mycorrhizal Fungi (BGC) in China, with accession number BGC XJ01, and in the National Microbial Resource Platform with accession number 1511C0001BGCAM0016.

[0029] like Figure 1 As shown, the multi-layered mesh bag for remediating molybdenum contamination in soil based on arbuscular mycorrhizal fungi of the present invention has an integrated structure with an open top and a sealed bottom. The inside of the mesh bag, from the outside to the inside, consists of a water-retaining nutrient layer 1, a heavy metal passivation layer 2, and a core microbial layer 3. The water-retaining nutrient layer material is a mixture of reed straw, vermiculite, and decomposed sheep manure in a mass ratio of 3:2:2. The heavy metal passivation layer material is a mixture of attapulgite, phosphate rock powder, and potassium humate in a mass ratio of 3:2:1. The core microbial layer material is a mixture of a dry arbuscular mycorrhizal fungi agent-peat soil mixture and a polyvinyl alcohol (PVA) water-soluble bag containing plant seeds. The polyvinyl alcohol (PVA) water-soluble bag containing plant seeds is preferably placed in the middle of the arbuscular mycorrhizal fungi agent-peat soil mixture.

[0030] The reed stalks have a particle size of 1-2 cm, the vermiculite has a particle size of 2-5 cm, and the attapulgite has a specific surface area ≥300 m². 2 / g, potassium humate contains ≥55% humic acid; arbuscular mycorrhizal fungicide and peat moss are mixed evenly at a mass ratio of 1:5, the arbuscular mycorrhizal fungicide is *Tetranychus mossae*, with a spore content ≥50 / g, peat moss organic matter content ≥70%, and pH value 5.5-6.5; each polyvinyl alcohol water-soluble bag contains 10-15 plant seeds.

[0031] The plant seeds mentioned are selected from herbaceous leguminous plants, preferably alfalfa seeds, white clover seeds, arrowhead pea seeds, or milkvetch seeds.

[0032] The multi-layer mesh bag for remediating molybdenum contamination in soil based on arbuscular mycorrhizal fungi is preferably a cylindrical three-dimensional structure. In one embodiment, the mesh bag has a diameter of 20 cm, a height of 15 cm, a mesh aperture of 0.5-1 cm, a water-retaining nutrient layer thickness of 3 cm, a heavy metal passivation layer thickness of 3 cm, and a core fungal layer diameter of 8 cm. However, this description is not intended to limit the invention.

[0033] The aforementioned multi-layered mesh bags for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi can be manufactured using the following method: Step 1: Making the mesh bag frame: Use flax fibers to weave a cylindrical mesh bag with a mesh size of 0.5-1cm. Sew a circular flax fabric bottom to seal the bottom of the mesh bag to prevent material leakage and ensure that the mesh bag has an integrated structure with an open top and a sealed bottom. Step 2: Layered Filling Material: A one-piece concentric three-layer ring structure plastic mold is used to assist in positioning and filling each layer of material, such as...Figure 2 As shown, the integrated concentric three-layer ring structure plastic mold includes an outer cylindrical ring part 4, a middle cylindrical ring part 5, and a central cylindrical ring part 6. The heights of the outer cylindrical ring part 4, the middle cylindrical ring part 5, and the central cylindrical ring part 6 are all the same as the height of the mesh bag. The outer cylindrical ring part 4, the middle cylindrical ring part 5, and the central cylindrical ring part 6 are connected into an integrated structure by a connecting plate 7. The connecting plate 7 is arranged radially along the outer cylindrical ring part 4, with one end connected to the outer side wall of the central cylindrical ring part 6 and the other end connected to the inner side wall of the outer cylindrical ring part 4. The connecting plate 7 is also connected to the middle cylindrical ring part 5, so that the outer cylindrical ring part 4, the middle cylindrical ring part 5, the central cylindrical ring part 6, and the connecting plate 7 form an integrated mold structure. The specific filling process for each layer of materials includes: placing the integrated concentric three-layer ring structure plastic mold into the mesh bag, with the outer cylindrical ring fitting tightly against the inner wall of the mesh bag, and the bottom of the mold fitting tightly against the bottom of the mesh bag; the cavity between the outer cylindrical ring and the middle cylindrical ring is the filling space for the water-retaining nutrient layer, the cavity between the middle cylindrical ring and the central cylindrical ring is the filling space for the heavy metal passivation layer, and the inner cavity of the central cylindrical ring is the filling space for the core bacterial layer. Pour water-retaining nutrient layer material into the cavity between the outer cylindrical ring and the middle cylindrical ring, and gently compact it with a pressure plate until the water-retaining nutrient layer material is flush with the top of the outer cylindrical ring; pour heavy metal passivation layer material into the cavity between the middle cylindrical ring and the central cylindrical ring, and similarly gently compact it until the heavy metal passivation layer material is flush with the top of the middle cylindrical ring; pour dry core fungal layer material into the inner cavity of the central cylindrical ring; place the polyvinyl alcohol water-soluble bag containing plant seeds in the middle of the arbuscular mycorrhizal fungi agent-peat soil mixture, and gently spread the arbuscular mycorrhizal fungi agent-peat soil mixture until it is flush with the top of the central cylindrical ring, without compaction; finally, slowly and vertically remove the integrated concentric three-layer ring structure plastic mold from the top of the mesh bag to complete the filling of each layer of material; Step 3: Dry storage: Store the prepared mesh bags in a dry and ventilated environment. The storage conditions are: temperature 15-25℃, relative humidity ≤40%, avoid direct sunlight, and take them out as needed.

[0034] Example 1: Pot Experiment Test soil: Soil was collected from tailings of the Luanchuan molybdenum mine in Luoyang. The basic physicochemical properties of the soil were as follows: molybdenum content 385.2 mg / kg, organic matter content 0.8%, pH value 7.2, water retention rate 9.5%, and aggregate structure ratio 3.2%.

[0035] Experimental setup: The experimental group used a multi-layered mesh bag designed in this invention for remediating molybdenum contamination in soil based on arbuscular mycorrhizal fungi. The bag was 20 cm in diameter and 15 cm in height, with a mesh size of 0.5 cm. The bag was an integrated structure with an open top and a sealed bottom. The bag contained, from the outside in, three layers: a water-retaining nutrient layer, a heavy metal passivation layer, and a core microbial inoculum layer. The control group used a regular flax mesh bag without layers, 20 cm in diameter and 15 cm in height. The regular flax mesh bag was filled with an equal amount of a mixture of the layers: the water-retaining nutrient layer, the heavy metal passivation layer, and the core microbial inoculum layer. A polyvinyl alcohol water-soluble bag containing plant seeds was placed in the middle of the mixture.

[0036] Test seeds: Alfalfa. Alfalfa seeds were placed in seed-specific polyvinyl alcohol water-soluble bags, with 12 alfalfa seeds per bag. The water-soluble bag film was 0.04 mm thick.

[0037] Test fungal agent: *Tetranychus mosierifolius*, spore content 50 spores / g.

[0038] Experimental design: Four treatment groups were set up, with three replicates in each group, as detailed below: Treatment Group 1 (Experimental Group): The multi-layer mesh bag based on arbuscular mycorrhizal fungi designed in this invention was used to remediate molybdenum pollution in soil. The multi-layer mesh bag was placed directly into the pot, with one mesh bag in each pot. The pot diameter was 22cm and the pot height was 18cm. After filling with molybdenum tailings soil, water was poured to activate the process. Treatment Group 2 (Mixed Control Group): Ordinary mesh bags without layered structure were used. The ordinary mesh bags were filled with an equal amount of the water-retaining nutrient layer material, heavy metal passivation layer material and core bacterial layer material described in this invention. A polyvinyl alcohol water-soluble bag containing 12 alfalfa seeds was placed in the middle of the mixture. One mesh bag was placed in each pot. The rest of the operation was the same as in Treatment Group 1. Treatment Group 3 (Plant Control Group): Ordinary mesh bags without layering were used. The ordinary mesh bags were filled with an equal amount of tailings soil. A polyvinyl alcohol water-soluble bag containing 12 alfalfa seeds was placed in the middle of the tailings soil. One mesh bag was placed in each pot. The rest of the operation was the same as in Treatment Group 1. Treatment group 4 (blank control group): Only molybdenum tailings soil was used, without placing mesh bags or seeds.

[0039] Experimental conditions: Greenhouse cultivation, temperature 22-25℃, light intensity 3500 lux, light duration 12h / d, regular watering to maintain soil moisture content 20-25%.

[0040] The following methods were used to determine the plant emergence rate, root mycorrhizal infection rate, soil molybdenum content, soil organic matter content, and soil water retention rate for each treatment group: Measurement method: (1) Plant emergence rate: The number of seedlings was observed and recorded on the 10th day after watering activation. Emergence rate = (actual number of seedlings / total number of seeds sown) × 100%. The emergence rate of the three potted plants in each treatment group was calculated, and the average value was taken as the emergence rate of the treatment group. The emergence rate of each treatment group was calculated according to this method. Refer to "Crop Seed Inspection Procedures Part 4: Sowing Quality Germination Test" (GB / T 3543.4-2025).

[0041] (2) Root mycorrhizal infection rate: After 120 days of culture, the complete root system of the plant was dug up, and the soil attached to the roots was thoroughly rinsed with clean water. Then, the roots were transparentized (if transparentization could not be performed immediately, the root samples should be completely immersed in a 50% ethanol solution to maintain the root tissue structure and prevent root tissue decay and degradation): The washed root samples were transferred to centrifuge tubes, and a sufficient amount of 10% KOH solution was added to ensure that the root samples were completely submerged. Then, the centrifuge tubes were heated in a 90℃ water bath for 60 min to make the root tissue transparent for easy observation. The transparentized root samples were acidified with 1% HCl, and then stained in a 90℃ water bath for 30 min using the ink-acetic acid method to stain the mycelium, vesicles, and arbuscular structures. After staining, the background color was washed away with lactic acid, and the root segments were cut into small segments of about 1 cm and placed on glass slides for preparation. Under a 400x optical microscope, the root segment was observed using a grid-crossing method. The root segment was placed under a micrometer with a grid on the eyepiece, and the presence or absence of mycorrhizal structures at each crosspoint was recorded. The infection rate was calculated as (number of infected crosspoints / total number of crosspoints) × 100%. This method, based on the classic staining procedure established by Phillips and Hayman (1970), has been widely used in ecological, agronomic, and soil microbiology research and has been included in several experimental textbooks, such as *Experimental Guide to Soil Microbiology* (China Agriculture Press) and *Mycorrhizal Symbiosis* (Smith & Read, 2008).

[0042] (3) Soil molybdenum content: After 120 days of cultivation, soil samples from each treatment group were taken, air-dried at room temperature, and impurities such as plant residues and stones were removed. The samples were then ground and passed through a 100-mesh nylon sieve to ensure uniformity. 1 g of the sieved soil sample was weighed and placed in a hard glass tube for complete digestion using a mixed acid digestion system. Concentrated nitric acid was first added to the hard glass tube and heated at 120°C for 2 hours for pre-digestion. Then, perchloric acid was added to the hard glass tube and the temperature was raised to 220°C until white fumes appeared and the solution became clear and transparent, indicating that molybdenum in the organic matter and mineral lattice had been completely released. After cooling, the digestion solution was diluted to 50 mL, filtered to remove insoluble matter, and then quantitatively analyzed using inductively coupled plasma mass spectrometry (ICP-MS). This method was based on the "Soil Testing Part 9: Determination of Available Molybdenum in Soil" (NY / T 1121.9-2023).

[0043] (4) Soil organic matter content: After 120 days of cultivation, soil samples from each treatment group were taken, air-dried at room temperature, and plant debris, stones, and other impurities were removed. The samples were then ground and passed through a 100-mesh nylon sieve to ensure uniformity. 0.3 g (accurate to 0.0001 g) of the sieved soil sample was weighed and placed in a hard glass tube. 5 mL of 0.8 mol / L potassium dichromate was added to the hard glass tube, followed by 7.5 mL of concentrated sulfuric acid, and the mixture was shaken thoroughly. The hard glass tube was placed in an oil bath and heated at 190°C for 5 min. After cooling, the tube wall was rinsed with distilled water and brought to a final volume. 1,000 phenanthroline was added, and the remaining potassium dichromate was titrated with a 0.2 mol / L ferrous sulfate standard solution. A blank test (without soil sample) was performed simultaneously. Based on the volume difference of ferrous sulfate consumed between the blank and the sample, the amount of potassium dichromate reduced by organic carbon was calculated, and the organic carbon content (g / kg) was then deduced. Since the average carbon content of soil organic matter is approximately 58%, the soil organic matter content (%) is obtained by multiplying the organic carbon content by a conversion factor of 1.724. This method is specifically described in "Soil Testing Part 6: Determination of Soil Organic Matter" (NY / T 1121.6-2006).

[0044] (5) Soil water retention rate (field water holding capacity): After 120 days of cultivation, soil samples from each treatment group were taken, air-dried at room temperature, and plant debris, stones, and other impurities were removed. The samples were then ground and passed through a 10-mesh nylon sieve. The sieved soil samples were then evenly packed into a 100 cm³ container. 3The soil sample was compacted in a ring cutter (the weight of which had been pre-weighed and recorded) to approximate the field bulk density. Distilled water was slowly added until the soil sample was completely saturated, with the water level slightly above the soil surface. The sample was then covered and left to stand for 24 hours to allow for full saturation. The ring cutter was then placed on a perforated tray and allowed to drain naturally at room temperature for 2 hours. The outer wall of the ring cutter was quickly wiped dry, and the total mass of the wet soil and ring cutter was measured. The soil sample, along with the ring cutter, was then dried in an oven at 105±2℃ until constant weight. After cooling in a desiccator, the total mass of the dry soil and ring cutter was measured. The wet soil weight and dry soil weight were calculated using the difference method, and the water retention rate was calculated using the formula: Water retention rate = [(Wet soil weight - Dry soil weight) / Dry soil weight] × 100%. This method is based on the "Soil Testing Part 22: Determination of Soil Field Water Holding Capacity—Ring Cutter Method" (NY / T1121.22-2010).

[0045] The results of the index measurements for each treatment group are as follows: Table 2. Results of index measurements for each treatment group in Example 1 Note: The value after "±" is the standard deviation.

[0046] As shown in Table 2, the experimental group of this invention significantly outperformed the three control groups in terms of plant emergence rate, mycorrhizal infection rate, and soil improvement effect. The reduction in soil molybdenum content reached 63.0%, far exceeding that of other treatment groups. Furthermore, the multi-layered mesh bags used in the experimental group for remediating soil molybdenum pollution based on arbuscular mycorrhizal fungi maintained an emergence rate of over 90% and showed no significant decrease in mycorrhizal infection rate after 6 months of storage, demonstrating its excellent storage stability.

[0047] Example 2: Field Trial The tailings accumulation area of ​​the Luanchuan molybdenum mine in Luoyang was selected, with an area of ​​1000m². 2 The basic physical and chemical properties of the soil are as follows: molybdenum content 426.5 mg / kg, organic matter content 0.7%, pH value 7.5, water retention rate 8.8%, and aggregate structure ratio 2.9%.

[0048] Experimental design: Two treatment groups were set up, with each group having a soil area of ​​500m². 2 Specifically: Experimental group: The multi-layered mesh bags designed in this invention for remediating molybdenum pollution in soil based on arbuscular mycorrhizal fungi (the mesh bags had been stored for 8 months) were used for planting, with a row spacing of 30cm and a plant spacing of 20cm, for a total of 8333 plants; Control group: Molybdenum pollution remediation was achieved through soil improvement and vegetation reconstruction. Specifically, 1.5 kg of soil amendment material was mixed into the soil of the molybdenum tailings at a rate of 1.5 kg per square meter. The soil amendment material was a mixture of rice straw crushed to 2-3 cm and humic acid, with a mass ratio of rice straw to humic acid of 100:30. After the rice straw and humic acid were mixed evenly, they were plowed into the soil to a depth of 0-20 cm to condition the soil's physical and chemical properties. Alfalfa seeds were cultivated into seedlings and then transplanted into the soil of the control group at the same planting density as the experimental group.

[0049] Field management: Regular drip irrigation after transplanting, three harvests per year (in April, July and October respectively). After harvesting, the experimental group was top-dressed with 100g of decomposed sheep manure per plant, while the control group was top-dressed with the same amount of the improved material (a mixture of rice straw and humic acid at a mass ratio of 100:30).

[0050] For two consecutive years, the indices of the experimental and control groups were measured. Soil molybdenum content after two years was determined according to the method in Example 1. The method for determining the cumulative harvested biomass over two years was as follows: At each harvest, three 1m × 1m quadrats were randomly set up in each treatment group. All aboveground plants within the quadrats were harvested, blanched at 105℃, and dried at a constant temperature of 65℃ until constant weight, then weighed. The average biomass (kg / m²) of all aboveground plants in the three quadrats of each treatment group at each harvest was calculated. 2 The six average biomasses obtained from six harvests over two years were added together to obtain the cumulative harvested biomass (kg / m³) for each treatment group over two years. 2 The results are shown in Table 3.

[0051] Table 3. Results of key indicators measured in the experimental and control groups in Example 2 Note: The value after "±" is the standard deviation.

[0052] Table 3 shows that after 2 years of remediation, the soil molybdenum content in the experimental group reached ≤100mg / kg, the vegetation coverage rate reached 92%, and the cumulative biomass was 2.1 times that of the control group. The remediation cost was reduced by 32.8% compared with the control group, and the planting efficiency was increased by 87.5%, achieving the goal of efficient, low-cost and easy-to-operate molybdenum tailings remediation.

[0053] Example 3: Wheat Planting Trial After Restoration Wheat was planted in the remediation-compliant area (soil molybdenum content 89.6 mg / kg) of Example 2 test group for verification (as the test group). Simultaneously, wheat was planted in unremediated molybdenum tailings soil as a control group. Each group had three replicate plots, each plot measuring 10 m². 2 The wheat variety used in the experiment was "USTC 1026" (National Approval Number 20210044). Each plot was planted using row sowing with a row spacing of 20cm and a planting depth of 10m. 20.225 kg (15 kg / mu) of seeds were sown in each plot at a depth of 3-5 cm, followed by covering with soil and compacting. Both the experimental and control groups adopted the same field water and fertilizer management plan. Before sowing, 80 kg of NPK compound fertilizer (N:P:K=15:15:15) was applied per mu as base fertilizer. During the wheat jointing stage, 15 kg of urea was applied per mu, and during the grain-filling stage, 10 kg of urea was applied per mu. The soil moisture content was maintained at 60%-70% of field capacity, and drainage was carried out in a timely manner during the rainy season to prevent waterlogging. The natural environmental conditions such as light and temperature in the planting areas were consistent.

[0054] The following methods were used to determine wheat survival rate, wheat yield, and wheat grain molybdenum content: (1) Wheat survival rate: 20 days after sowing, the number of wheat plants that emerged normally and grew vigorously in each plot was counted, and the wheat survival rate was calculated as follows: Wheat survival rate = number of surviving plants / number of sown plants × 100%. The calculation of the number of sown plants was based on: each 10m² plot... 2 The seeding rate in the plot was 0.225 kg, and the thousand-grain weight of wheat was 44.6 g. Each plot was 10 m². 2 Number of plants sown in the plot = (0.225 × 1000) ÷ (44.6 ÷ 1000) ≈ 5045 plants.

[0055] (2) Wheat yield: After the wheat is fully mature (about 210 days after sowing, when the wheat ears turn yellow and the grains harden), the yield is measured for each 10m². 2 The entire plot was harvested, threshed, and impurities were removed from the wheat ears to obtain clean wheat grains. The clean wheat grains were then dried in a 65℃ constant-temperature oven until constant weight, and the weight was recorded for each 10m³ plot. 2 Dry weight of grains in the plot (kg / 10m³) 2 To calculate wheat yield per acre, use the following formula: Yield per acre (kg / acre) = Dry weight of grains in the plot (kg) ÷ 10 (m² / acre) 2 ) × 666.67 (m 2 / mu).

[0056] (3) Determination of molybdenum content in wheat grains: The harvested wheat grains were rinsed with ultrapure water to remove surface impurities, blanched at 105℃, dried at 80℃ to constant weight, pulverized with a pulverizer, sieved, and sealed for storage. 1g of the sieved sample was weighed into a PTFE digestion vessel, and nitric acid was added for digestion. After digestion, the sample was allowed to cool naturally to room temperature. The digestion solution was transferred to a volumetric flask, and the digestion vessel was washed three times with ultrapure water. The washing solution was added to the volumetric flask, and the volume was adjusted to the mark. The solution was shaken well and set aside. A blank experiment was also performed (the blank experiment did not include wheat sample, but the other steps were the same). The molybdenum content in wheat grains was determined by graphite furnace atomic absorption spectrometry according to the National Food Safety Standard for Determination of Molybdenum in Food (GB 5009.297-2023).

[0057] The measurement results are shown in Table 4 below: Table 4. Results of index measurement in the experimental and control groups in Example 3 Note: The value after "±" is the standard deviation.

[0058] Table 4 shows that the survival rate of wheat planted in the remediated molybdenum mine tailings area reached 95%, with a yield of 320 kg / mu and a molybdenum content of 0.35 mg / kg in the wheat grains. In contrast, the survival rate of wheat planted in the unremediated control area was only 30%, with a yield of 31.6 kg / mu and a molybdenum content of 1.2 mg / kg in the grains. This indicates that the remediated molybdenum mine tailings soil significantly reduced the molybdenum content in wheat grains and increased wheat yield.

[0059] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, preferred embodiments are described in order to avoid redundancy. However, this invention is not intended to limit the invention in any way. Therefore, any simple modifications, equivalent changes and alterations made by any person skilled in the art to the above embodiments based on the technical essence of this invention without departing from the scope of the technical solution of this invention shall still fall within the scope of the technical solution of this invention.

Claims

1. A multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi, characterized in that, The mesh bag is an integrated structure with an open top and a sealed bottom. From the outside to the inside, the mesh bag is filled with a water-retaining nutrient layer material, a heavy metal passivation layer material, and a core microbial inoculum layer material. The water-retaining nutrient layer material is a mixture of reed straw, vermiculite, and decomposed sheep manure in a mass ratio of 3:2:

2. The heavy metal passivation layer material is a mixture of attapulgite clay, phosphate rock powder, and potassium humate in a mass ratio of 3:2:

1. The core microbial inoculum layer material is a mixture of arbuscular mycorrhizal fungi agent and peat moss, and a polyvinyl alcohol water-soluble bag containing seeds.

2. The multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi as described in claim 1, characterized in that, The reed stalks have a particle size of 1-2 cm, the vermiculite has a particle size of 2-5 cm, and the attapulgite has a specific surface area ≥300 m². 2 / g, potassium humate contains ≥55% humic acid; arbuscular mycorrhizal fungicide and peat moss are mixed evenly at a mass ratio of 1:5, the arbuscular mycorrhizal fungicide is *Tetranychus mossae*, with a spore content ≥50 / g, peat moss organic matter content ≥70%, and pH value 5.5-6.5; each polyvinyl alcohol water-soluble bag contains 10-15 seeds.

3. The multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi as described in claim 1 or 2, characterized in that, The seeds mentioned are selected from the seeds of herbaceous leguminous plants.

4. The multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi as described in claim 1 or 2, characterized in that, The seeds used are alfalfa seeds, white clover seeds, arrowhead pea seeds, or milkvetch seeds.

5. The multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi as described in claim 1 or 2, characterized in that, The mesh bag is a cylindrical mesh bag woven from flax fibers. The mesh size of the bag is 0.5-1cm, and the bottom of the bag is sealed with flax fabric.

6. The multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi as described in claim 1 or 2, characterized in that, The production method includes: Step 1: Making the mesh bag frame: Use flax fibers to weave a cylindrical mesh bag with a mesh size of 0.5-1cm. Sew a circular flax fabric bottom to seal the bottom of the mesh bag to prevent material leakage and ensure that the mesh bag has an integrated structure with an open top and a sealed bottom. Step 2: Layered Filling Material: An integrated concentric three-layer ring structure plastic mold is used for positioning and filling. The integrated concentric three-layer ring structure plastic mold includes an outer cylindrical ring, a middle cylindrical ring, and a central cylindrical ring. The specific filling process is as follows: The integrated concentric three-layer ring structure plastic mold is placed inside the mesh bag. The outer cylindrical ring is tightly fitted to the inner wall of the mesh bag, and the bottom of the mold is tightly fitted to the bottom of the mesh bag. The cavity between the outer cylindrical ring and the middle cylindrical ring is the filling space for the water-retaining nutrient layer. The cavity between the middle cylindrical ring and the central cylindrical ring is the filling space for the heavy metal passivation layer. The inner cavity of the central cylindrical ring is the filling space for the core bacterial layer. Pour water-retaining nutrient layer material into the cavity between the outer cylindrical ring and the middle cylindrical ring, and gently compact it with a pressure plate until the water-retaining nutrient layer material is flush with the top of the outer cylindrical ring; pour heavy metal passivation layer material into the cavity between the middle cylindrical ring and the central cylindrical ring, and gently compact it until the heavy metal passivation layer material is flush with the top of the middle cylindrical ring; pour dry core microbial culture layer material into the inner cavity of the central cylindrical ring, spread it gently without compaction, and finally slowly and vertically remove the integrated concentric three-layer ring structure plastic mold from the top of the mesh bag to complete the layered filling; Step 3: Dry storage: Store the prepared mesh bags in a dry and ventilated environment. The storage conditions are: temperature 15-25℃, relative humidity ≤40%, avoid direct sunlight, and take them out as needed.

7. The multi-layer mesh bag for remediating molybdenum-contaminated soil based on arbuscular mycorrhizal fungi as described in claim 6, characterized in that, The outer cylindrical annular component, the middle cylindrical annular component, and the central cylindrical annular component are connected as an integral structure by a connecting plate. The connecting plate is arranged radially along the outer cylindrical annular component, with one end connected to the outer wall of the central cylindrical annular component and the other end connected to the inner wall of the outer cylindrical annular component. The connecting plate is also connected to the middle cylindrical annular component, so that the outer cylindrical annular component, the middle cylindrical annular component, the central cylindrical annular component, and the connecting plate form an integral structure mold.

8. The application of the multi-layer mesh bag based on arbuscular mycorrhizal fungi for remediating molybdenum contamination in molybdenum tailings soil remediation as described in claim 1 or 2.

9. The application as described in claim 8, characterized in that, The application method includes the following steps: (1) Site pretreatment: Clean up large gravel and impurities in the molybdenum tailings area to be repaired, plow the tailings sand to 20-30cm, level the land and mark the planting points with a row spacing of 30cm and a plant spacing of 20cm. (2) Planting in pits: Dig planting pits at the planting point. The depth and diameter of the planting pits should be matched with the size of the multi-layer mesh bags for remediating molybdenum pollution in the soil, and reserve space for backfilling. Place the stored multi-layer mesh bags for remediating molybdenum pollution in the soil directly into the planting pits, ensuring that the top of the mesh bags is flush with the ground surface. Then backfill and compact the surrounding tailings soil to prevent the mesh bags from shaking. (3) Irrigation activation: Water immediately after planting to activate the fungus. The amount of water for each planting point is 500-800mL. Ensure that the materials in each layer of the net bag are fully moistened. The polyvinyl alcohol water-soluble bag containing seeds in the core fungal layer dissolves when it comes into contact with water, releasing the seeds and activating the germination of arbuscular mycorrhizal fungal spores. Afterward, maintain the soil moisture content at 18-25% and drain water in time during the rainy season to prevent waterlogging. (4) Harvesting and recycling: After the seed plants have grown for 90-100 days, use a harvester to harvest the above-ground parts at a height of 5-8cm from the ground surface. Transport the harvested plants to a professional treatment plant for incineration and recover molybdenum resources from the ash. After harvesting, apply 100g of well-rotted sheep manure per plant to promote regeneration.

10. The application as described in claim 9, characterized in that, The restoration cycle is 2-3 years, and the above-ground parts of the plants are harvested 3-4 times a year.

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