A three-dimensional repair configuration method of garden plants for heavy metal contaminated soil

Abstract

The present application relates to the technical field of soil pollution ecological restoration, and discloses a kind of garden plant three-dimensional repair configuration method of heavy metal contaminated soil, comprising the following steps: site evaluation and preparation, plant material selection, three-dimensional configuration planting, exogenous nitrogen intensification control, maintenance management and harvesting;By selecting red leaf adenostyli, small chrysanthemum and oil sunflower with different root depths to construct three-dimensional configuration of arbor-shrub-herb three layers, make deep-rooted arbor fix and absorb cadmium in deep soil, middle layer root flower enrich and transport cadmium in middle layer soil to the aboveground part, shallow-rooted herb enrich lead in surface soil, three of them realize layered repair to contaminated soil whole layer, give full play to the complementary advantages of different plants in root distribution, heavy metal enrichment capacity and tolerance, improve overall repair efficiency, solve the problem that deep heavy metal is difficult to remove.

Description

Technical Field

[0001] This invention relates to the field of soil pollution ecological remediation technology, specifically a method for the three-dimensional remediation configuration of garden plants for heavy metal contaminated soil. Background Technology

[0002] Soil is an indispensable natural resource for human survival and social development, and a crucial foundation for agricultural production. With the increasing severity of industrial and urban pollution and the growing variety and quantity of agricultural chemicals, soil pollution in my country is becoming increasingly serious, with metal pollution being the most prominent issue. Heavy metals are a class of toxic and potentially hazardous pollutants that can accumulate in soil and organisms. When their concentrations reach certain levels, they not only lead to soil degradation and reduced crop yields, but may even enter the food chain, endangering human health and safety.

[0003] Currently, most phytoremediation technologies for heavy metal contaminated soils employ single plant species or simple mixed planting patterns, which fail to fully utilize the complementary advantages of different plants in terms of root depth, heavy metal accumulation capacity, and tolerance, resulting in low remediation efficiency, especially for the effective removal of heavy metals in deep soil layers.

[0004] Therefore, a three-dimensional remediation method for garden plants in heavy metal contaminated soil is proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for the three-dimensional remediation of heavy metal contaminated soil using garden plants, which solves the problems of low remediation efficiency, especially the difficulty in effectively removing heavy metals from deep soil layers, as mentioned in the background.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for three-dimensional remediation of heavy metal contaminated soil using garden plants, comprising the following steps: Step 1: Site assessment and preparation. The heavy metal content of the contaminated soil to be remediated is tested to determine whether it is suitable for single Cd pollution, single Pb pollution, or Cd-Pb combined pollution. The Cd concentration range is 0.3-100 mg / kg, the Pb concentration range is 50-100 mg / kg, and the Cd-Pb combined pollution concentration range is Cd≤100 mg / kg and Pb≤100 mg / kg. The soil pH value is 5.5-7.5. Step 2: Plant material selection. Select a combination of three layers of ornamental plants with different restorative functions: trees, shrubs and herbs. The trees are red-leaved glandular willows, the shrubs are small chrysanthemums 'Eastern Fence Little Mushroom', and the herbs are sunflowers. Step 3: Three-dimensional planting configuration. A three-dimensional configuration mode combining a three-layer vertical structure of trees-shrubs-herbs with horizontal staggered planting is adopted. The red-leaf willow, chrysanthemum and sunflower are planted according to the preset plant spacing and density. Step 4: Enhanced regulation of exogenous nitrogen. Apply nitrogen fertilizer in several applications before and after planting. The nitrogen fertilizer is urea. The total application rate is 260-300 mg N / kg soil, based on the weight of the topsoil layer of 0-20 cm. Step 5: Maintenance and harvesting. Regularly irrigate with nutrient solution and manage water. Harvest the above-ground parts of the plants at specific growth stages and collect the harvested materials for harmless treatment.

[0007] Preferably, in step one, when the original soil to be repaired has poor physical and chemical properties, substrate improvement is carried out before planting. The substrate improvement formula is: the volume ratio of perlite, vermiculite and original soil is 0.8-1.2:0.8-1.2:1.8-2.2, or 10%-15% of well-rotted organic fertilizer is added to the original soil.

[0008] Preferably, in step two, the red-leaved glandular willow is a deciduous tree with a root system depth of 1.5-2.0m, used for the fixation and absorption of Cd in deep soil; the chrysanthemum is a perennial flower of the Asteraceae family with a Cd translocation coefficient TF>1.0, used for the enrichment of Cd in the middle soil and translocation to the aboveground parts; and the sunflower is an annual herb of the Asteraceae family with a single plant dry weight of 250g-350g, used for the enrichment of Pb in the surface soil.

[0009] Preferably, in step three, the planting season is spring or autumn, with spring planting in March-April when the soil temperature is 12℃-18℃ and autumn planting in September-October when the soil temperature is 15℃-25℃; the soil moisture content is maintained at 60%-80% of field capacity during planting.

[0010] Preferably, in step three, the vertical structure of the three-dimensional configuration mode is as follows: the upper layer is red willow with a plant height of 2.5-3.0m and a crown width of 1.0-1.2m, the middle layer is chrysanthemum with a plant height of 0.4-0.6m, and the lower layer is sunflower with a plant height of 1.5-2.0m.

[0011] Preferably, in step three, the horizontal planting parameters are as follows: the spacing between plants of red-leaf glandular willow is 50cm, the row spacing is 50cm, and the density is 4 plants / m², using a plum blossom planting pattern, with hole dimensions of 40cm×40cm×40cm; the spacing between plants of chrysanthemum is 20cm, the row spacing is 20cm, and the density is 25 plants / m², interspersed among the red-leaf glandular willow plants, with a distance of 30cm from the main trunk of the willow; the spacing between plants of sunflower is 30cm, the row spacing is 30cm, and the density is 11 plants / m², planted on the periphery and in gaps, staggered by 10cm from the chrysanthemum.

[0012] Preferably, in step four, the application schedule of urea is as follows: 40%-60% of the total amount is applied as base fertilizer before planting, and the remaining amount is applied as top dressing 20-40 days after planting; the application method is trench application or hole application, followed by covering with soil.

[0013] Preferably, in step five, the nutrient solution is a modified Hoagland nutrient solution, the formula of which contains the following components at the following concentrations: calcium nitrate tetrahydrate 900-1000 mg / L, potassium nitrate 480-530 mg / L, magnesium sulfate heptahydrate 470-520 mg / L, potassium dihydrogen phosphate 130-140 mg / L, boric acid 2.5-3.0 mg / L, manganese sulfate tetrahydrate 2.0-2.3 mg / L, zinc sulfate heptahydrate 0.2-0.25 mg / L, copper sulfate pentahydrate 0.06-0.10 mg / L, ammonium molybdate tetrahydrate 0.01-0.03 mg / L, and sodium iron ethylenediaminetetraacetate 18-22 mg / L; the irrigation frequency is once every 5-9 days, 180-220 mL per plant each time.

[0014] Preferably, in step five, the harvesting management includes: harvesting the above-ground parts of chrysanthemums in mid-to-late November after the flowering period ends, leaving a stubble height of 3-7cm; harvesting the entire sunflower plant in September-October after the seeds mature, with the flower heads and stems treated separately; and pruning the branches of red-leaved willow in December after leaf fall, retaining the main stem. The harvested materials are then sent to a hazardous waste treatment center for high-temperature incineration or safe landfill.

[0015] Preferably, step five also includes crop rotation management, where the sunflowers are re-sown annually, the chrysanthemums can overwinter perennially, and the red-leaved glandular willows are managed as perennials; after 3-5 years of continuous restoration, the soil heavy metal content is tested, and once it meets the standards, it is converted to routine garden maintenance.

[0016] Compared with existing technologies, this invention provides a method for the three-dimensional remediation of heavy metal contaminated soil using garden plants, which has the following beneficial effects: 1. In this invention, a three-dimensional configuration of trees, shrubs, and herbs with different root depths is constructed by selecting red-leaved glandular willow, chrysanthemum, and sunflower. This allows deep-rooted trees to fix and absorb cadmium in the deep soil, mid-layer perennial flowers to accumulate and transport cadmium from the mid-layer soil to the above-ground parts, and shallow-rooted herbs to accumulate lead in the surface soil. The three work together to achieve stratified remediation of the entire soil layer of contaminated soil, giving full play to the complementary advantages of different plants in root distribution, heavy metal accumulation capacity, and tolerance, thereby improving the overall remediation efficiency and solving the problem of difficult removal of deep heavy metals.

[0017] 2. In this invention, exogenous nitrogen fertilizer is applied to enhance regulation based on a three-dimensional configuration. Urea is applied in stages before and after planting, which can supply nutrients according to the different growth stages of plants. The base fertilizer provides sufficient nitrogen source for early rooting and growth of plants, while the top dressing supplements nutrients during the rapid growth period of plants, promotes the accumulation of plant biomass and root development, thereby enhancing the plant's ability to absorb and transport heavy metals and strengthening the repair effect.

[0018] 3. In this invention, different plants are harvested and managed in a targeted manner at their respective suitable growth stages. The above-ground parts of chrysanthemums are harvested after the flowering period, the whole plant of sunflowers is harvested after the seeds mature, and the branches of red-leaved glandular willows are pruned after the leaves fall. The harvested materials are then sent to a hazardous waste treatment center for high-temperature incineration and safe landfill, thereby removing heavy metals from the soil and reducing secondary pollution. At the same time, the crop rotation system of overwintering perennial chrysanthemums and perennial management of red-leaved glandular willows is used to maintain the continuity and stability of the restored community. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the three-dimensional repair configuration mode of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0021] For specific implementation examples, please refer to: Figure 1 Example 1: A method for three-dimensional remediation of heavy metal contaminated soil using garden plants, comprising the following steps: Step 1: Site assessment and preparation. The heavy metal content of the contaminated soil to be remediated is tested to determine its suitability for single Cd contamination, with a Cd concentration of 30 mg / kg and a soil pH of 5.5. Step 2: Plant material selection. Select a three-tiered garden ornamental plant combination of trees, shrubs and herbs with different restoration functions. The tree is red-leaved glandular willow, the shrub is 'Eastern Fence Little Mushroom' chrysanthemum, and the herb is sunflower. Step 3: Three-dimensional planting configuration. A three-dimensional configuration mode combining a three-layer vertical structure of trees, shrubs and herbs with horizontal staggered planting is adopted. Red-leaved glandular willow, chrysanthemum and sunflower are planted according to the preset plant spacing and density. Step 4: Enhanced regulation of exogenous nitrogen. Apply nitrogen fertilizer in two separate applications before and after planting. The nitrogen fertilizer is urea, with a total application rate of 260 mg N / kg soil. Step 5: Maintenance and harvesting. Regularly irrigate with nutrient solution and manage water. Harvest the above-ground parts of the plants at specific growth stages and collect the harvested materials for harmless treatment.

[0022] In step one, when the original soil to be repaired has poor physical and chemical properties, substrate improvement is carried out before planting. The substrate improvement formula is: perlite, vermiculite and original soil in a volume ratio of 0.8:0.8:1.8.

[0023] In step two, *Salix rubrum* is a deciduous tree with a root system reaching a depth of 1.5m, used for the fixation and absorption of Cd in deep soil; *Chrysanthemum morifolium* is a perennial flowering plant of the Asteraceae family with a Cd translocation coefficient TF > 1.0, used for the enrichment of Cd in the middle soil and its translocation to the aboveground parts; and *Sunflower* is an annual herb of the Asteraceae family with a single plant dry weight of 250g, used for the enrichment of Pb in the surface soil.

[0024] In step three, the planting season is spring, with the planting time in March, the soil temperature is 12℃, and the soil moisture content is maintained at 60% of field capacity.

[0025] In step three, the vertical structure of the three-dimensional configuration mode is as follows: the upper layer is red willow with a plant height of 2.5m and a crown width of 1.0m, the middle layer is chrysanthemum with a plant height of 0.4m, and the lower layer is sunflower with a plant height of 1.5m.

[0026] In step three, the horizontal planting parameters are as follows: the spacing between plants of red-leaf glandular willow is 50cm, the row spacing is 50cm, and the density is 4 plants / m². It is planted in a plum blossom pattern, and the hole size is 40cm×40cm×40cm. The spacing between plants of chrysanthemum is 20cm, the row spacing is 20cm, and the density is 25 plants / m². It is interspersed among the red-leaf glandular willow plants, with a distance of 30cm from the main trunk of the willow. The spacing between plants of sunflower is 30cm, the row spacing is 30cm, and the density is 11 plants / m². It is planted on the periphery and in the gaps, staggered by 10cm from the chrysanthemum.

[0027] In step four, the application schedule for urea is as follows: 40% of the total amount is applied as base fertilizer before planting, and the remaining amount is applied as top dressing 20 days after planting; the application method is trench application, followed by covering with soil.

[0028] In step five, the nutrient solution is a modified Hogrange nutrient solution, whose formula contains the following components at the following concentrations: calcium nitrate tetrahydrate 900 mg / L, potassium nitrate 480 mg / L, magnesium sulfate heptahydrate 470 mg / L, potassium dihydrogen phosphate 130 mg / L, boric acid 2.5 mg / L, manganese sulfate tetrahydrate 2.0 mg / L, zinc sulfate heptahydrate 0.2 mg / L, copper sulfate pentahydrate 0.06 mg / L, ammonium molybdate tetrahydrate 0.01 mg / L, and sodium iron ethylenediaminetetraacetate 18 mg / L; the watering frequency is once every 5 days, 180 mL per plant each time.

[0029] In step five, harvesting management includes: chrysanthemums are harvested from the ground in mid-to-late November after flowering, leaving a stubble height of 3cm; sunflowers are harvested from the whole plant in September after the seeds mature, with the flower heads and stems treated separately; red-leaved glandular willows are pruned in December after leaf fall, retaining the main stem; the harvested materials are sent to a hazardous waste treatment center for high-temperature incineration.

[0030] Step five also includes crop rotation management, with sunflowers being re-sown annually, chrysanthemums being able to overwinter perennially, and red-leaved glandular willows being managed as perennials; after three years of continuous restoration, the soil heavy metal content is tested, and once it meets the standards, it is transferred to regular landscaping maintenance.

[0031] Please see Figure 1 Example 2: A method for three-dimensional remediation of heavy metal contaminated soil using garden plants, comprising the following steps: Step 1: Site assessment and preparation. The heavy metal content of the contaminated soil to be remediated is tested to determine whether it is suitable for single Pb contamination, where the Pb concentration is 50 mg / kg and the soil pH is 6.5. Step 2: Plant material selection. Select a three-tiered garden ornamental plant combination of trees, shrubs and herbs with different restoration functions. The tree is red-leaved glandular willow, the shrub is 'Eastern Fence Little Mushroom' chrysanthemum, and the herb is sunflower. Step 3: Three-dimensional planting configuration. A three-dimensional configuration mode combining a three-layer vertical structure of trees, shrubs and herbs with horizontal staggered planting is adopted. Red-leaved glandular willow, chrysanthemum and sunflower are planted according to the preset plant spacing and density. Step 4: Enhanced regulation of exogenous nitrogen. Apply nitrogen fertilizer in two separate applications before and after planting. The nitrogen fertilizer is urea, with a total application rate of 280 mg N / kg soil. Step 5: Maintenance and harvesting. Regularly irrigate with nutrient solution and manage water. Harvest the above-ground parts of the plants at specific growth stages and collect the harvested materials for harmless treatment.

[0032] In step one, when the original soil to be repaired has poor physical and chemical properties, substrate improvement is carried out before planting. The substrate improvement formula is: perlite, vermiculite and original soil in a volume ratio of 1:1:2.

[0033] In step two, *Salix rubrum* is a deciduous tree with a root system reaching a depth of 1.7m, used for the fixation and absorption of Cd in deep soil; *Chrysanthemum morifolium* is a perennial flowering plant of the Asteraceae family with a Cd translocation coefficient TF > 1.0, used for the enrichment of Cd in the middle soil and its translocation to the aboveground parts; and *Sunflower* is an annual herb of the Asteraceae family with a single plant dry weight of 300g, used for the enrichment of Pb in the surface soil.

[0034] In step three, the planting season is autumn, the planting time is September, and the soil temperature is 20℃; the soil moisture content is maintained at 70% of field capacity during planting.

[0035] In step three, the vertical structure of the three-dimensional configuration mode is as follows: the upper layer is red willow with a plant height of 2.7m and a crown width of 1.1m, the middle layer is chrysanthemum with a plant height of 0.5m, and the lower layer is sunflower with a plant height of 1.7m.

[0036] In step three, the horizontal planting parameters are as follows: the spacing between plants of red-leaf glandular willow is 50cm, the row spacing is 50cm, and the density is 4 plants / m². It is planted in a plum blossom pattern, and the hole size is 40cm×40cm×40cm. The spacing between plants of chrysanthemum is 20cm, the row spacing is 20cm, and the density is 25 plants / m². It is interspersed among the red-leaf glandular willow plants, with a distance of 30cm from the main trunk of the willow. The spacing between plants of sunflower is 30cm, the row spacing is 30cm, and the density is 11 plants / m². It is planted on the periphery and in the gaps, staggered by 10cm from the chrysanthemum.

[0037] In step four, the application schedule for urea is as follows: 50% of the total amount is applied as base fertilizer before planting, and the remaining amount is applied as top dressing 30 days after planting; the application method is hole application, followed by covering with soil.

[0038] In step five, the nutrient solution is a modified Hogrange nutrient solution, whose formula contains the following components at the following concentrations: calcium nitrate tetrahydrate 950 mg / L, potassium nitrate 510 mg / L, magnesium sulfate heptahydrate 500 mg / L, potassium dihydrogen phosphate 135 mg / L, boric acid 2.7 mg / L, manganese sulfate tetrahydrate 2.1 mg / L, zinc sulfate heptahydrate 0.22 mg / L, copper sulfate pentahydrate 0.08 mg / L, ammonium molybdate tetrahydrate 0.02 mg / L, and sodium iron ethylenediaminetetraacetate 20 mg / L; the watering frequency is once every 7 days, 200 mL per plant each time.

[0039] In step five, harvesting management includes: chrysanthemums are harvested from the ground in mid-to-late November after flowering, leaving a stubble height of 5cm; sunflowers are harvested from the whole plant in September after the seeds mature, with the flower heads and stems treated separately; red-leaved glandular willows are pruned in December after leaf fall, retaining the main stem; the harvested materials are collected and sent to a hazardous waste treatment center for safe landfill.

[0040] Step five also includes crop rotation management, with sunflowers being re-sown annually, chrysanthemums being able to overwinter perennially, and red-leaved glandular willows being managed as perennials; after four years of continuous restoration, the soil heavy metal content is tested, and once it meets the standards, it is transferred to regular landscaping maintenance.

[0041] Please see Figure 1 Example 3: A method for three-dimensional remediation of heavy metal contaminated soil using garden plants, comprising the following steps: Step 1: Site assessment and preparation. The heavy metal content of the contaminated soil to be remediated is tested to determine that it is suitable for Cd-Pb combined pollution, with Cd concentration of 80 mg / kg, Pb concentration of 90 mg / kg, and soil pH of 7.5. Step 2: Plant material selection. Select a three-tiered garden ornamental plant combination of trees, shrubs and herbs with different restoration functions. The tree is red-leaved glandular willow, the shrub is 'Eastern Fence Little Mushroom' chrysanthemum, and the herb is sunflower. Step 3: Three-dimensional planting configuration. A three-dimensional configuration mode combining a three-layer vertical structure of trees, shrubs and herbs with horizontal staggered planting is adopted. Red-leaved glandular willow, chrysanthemum and sunflower are planted according to the preset plant spacing and density. Step 4: Enhanced regulation of exogenous nitrogen. Apply nitrogen fertilizer in two separate applications before and after planting. The nitrogen fertilizer is urea, with a total application rate of 300 mg N / kg soil. Step 5: Maintenance and harvesting. Regularly irrigate with nutrient solution and manage water. Harvest the above-ground parts of the plants at specific growth stages and collect the harvested materials for harmless treatment.

[0042] In step one, when the original soil to be repaired has poor physical and chemical properties, substrate improvement is carried out before planting by adding 10% well-rotted organic fertilizer by volume to the original soil.

[0043] In step two, *Salix matsudana* is a deciduous tree with a root system reaching a depth of 2.0m, used for the fixation and absorption of Cd in deep soil. *Chrysanthemum morifolium* is a perennial flowering plant of the Asteraceae family with a Cd translocation coefficient TF > 1.0, used for the enrichment of Cd in the middle soil and its translocation to the aboveground parts. *Sunflower* is an annual herb of the Asteraceae family with a single plant dry weight of 350g, used for the enrichment of Pb in the surface soil.

[0044] In step three, the planting season is spring, with the spring planting time being April and the soil temperature being 18℃; the soil moisture content is maintained at 80% of field capacity during planting.

[0045] In step three, the vertical structure of the three-dimensional configuration mode is as follows: the upper layer is red willow with a plant height of 3.0m and a crown width of 1.2m, the middle layer is chrysanthemum with a plant height of 0.6m, and the lower layer is sunflower with a plant height of 2.0m.

[0046] In step three, the horizontal planting parameters are as follows: the spacing between plants of red-leaf glandular willow is 50cm, the row spacing is 50cm, and the density is 4 plants / m². It is planted in a plum blossom pattern, and the hole size is 40cm×40cm×40cm. The spacing between plants of chrysanthemum is 20cm, the row spacing is 20cm, and the density is 25 plants / m². It is interspersed among the red-leaf glandular willow plants, with a distance of 30cm from the main trunk of the willow. The spacing between plants of sunflower is 30cm, the row spacing is 30cm, and the density is 11 plants / m². It is planted on the periphery and in the gaps, staggered by 10cm from the chrysanthemum.

[0047] In step four, the application schedule for urea is as follows: 60% of the total amount is applied as base fertilizer before planting, and the remaining amount is applied as top dressing 40 days after planting; the application method is trench application, followed by covering with soil.

[0048] In step five, the nutrient solution is a modified Hogrange nutrient solution, whose formula contains the following components at the following concentrations: calcium nitrate tetrahydrate 1000 mg / L, potassium nitrate 530 mg / L, magnesium sulfate heptahydrate 520 mg / L, potassium dihydrogen phosphate 140 mg / L, boric acid 3.0 mg / L, manganese sulfate tetrahydrate 2.3 mg / L, zinc sulfate heptahydrate 0.25 mg / L, copper sulfate pentahydrate 0.10 mg / L, ammonium molybdate tetrahydrate 0.03 mg / L, and sodium iron ethylenediaminetetraacetate 22 mg / L; the irrigation frequency is once every 9 days, with 220 mL per plant each time.

[0049] In step five, harvesting management includes: chrysanthemums are harvested from the ground in mid-to-late November after flowering, leaving a stubble height of 7cm; sunflowers are harvested from the whole plant in October after the seeds mature, with the flower heads and stems treated separately; red-leaved glandular willows are pruned in December after leaf fall, retaining the main stem; the harvested materials are sent to a hazardous waste treatment center for high-temperature incineration.

[0050] Step five also includes crop rotation management, with sunflowers being re-sown annually, chrysanthemums being able to overwinter perennially, and red-leaved glandular willows being managed as perennials; after 5 years of continuous restoration, the soil heavy metal content is tested, and once it meets the standards, it is transferred to regular landscaping maintenance.

[0051] Comparative Example 1: The difference between this comparative example and Example 1 is that no willow trees were planted in this comparative example during the restoration configuration; only sunflowers in the middle layer and chrysanthemums in the lower layer were planted.

[0052] Comparative Example 2 differs from Example 1 in that: no modified Hogland nutrient solution was used in the repair preparation of this comparative example; only conventional garden soil was used for planting.

[0053] Comparative Example 3 differs from Example 1 in that: in this comparative example, urea was not applied in multiple applications after planting, but all urea was applied to the soil as base fertilizer at once before planting.

[0054] Comparative Example 4 differs from Example 1 in that the plant arrangement in this comparative example is not layered according to a vertical structure, but rather willows, sunflowers and chrysanthemums are planted together on the same horizontal plane.

[0055] The performance of the three-dimensional remediation configuration methods for heavy metal contaminated soil constructed in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and methods are as follows: Heavy metal enrichment capacity testing was conducted on the 90th day after plant planting. Soil samples were collected from the upper layer of tree roots and plants, the middle layer of shrub roots and plants, and the lower layer of herbaceous roots and plants. The above-ground parts and underground roots of the plants were blanched in an oven at 105℃ for 30 minutes, then dried at 80℃ to constant weight and weighed. The dried samples were digested using a 4:1 nitric acid-perchloric acid digestion system, and the Cd and Pb content was determined using atomic absorption spectrometry. The enrichment coefficient of heavy metals per unit mass of above-ground plant parts was calculated. Plant biomass accumulation test: Samples were taken at the maturity stage of plant planting. After the whole plant was dug up, the soil attached to the roots was washed off, and the above-ground parts and underground roots were distinguished. After blanching at 105℃ for 30 minutes, the plants were dried in a constant temperature drying oven at 80℃ until constant weight. The dry weight was recorded by weighing with an electronic balance. The total biomass dry weight of the plant community was measured and recorded. Soil physicochemical properties were tested. Soil samples were collected from the top 0-20cm and the deep 40-60cm layers of each treatment group before planting and on day 180 of remediation. The soil pH was measured using the glass electrode method with a water-to-soil ratio of 2.5:1 and shaking for 30 minutes. The change in soil pH was calculated. The continuous repair cycle test simulates the natural growth environment and records the time points from planting to the first flowering and fruiting of plants under each configuration mode to evaluate the survival rate and adaptability of plant communities under continuous growth conditions. The plant height, crown width and the occurrence of diseases and pests of each layer of plants are recorded regularly every 30 days. The 180-day survival rate of plant communities under each configuration mode is statistically calculated to examine the long-term tolerance of different plant configurations to heavy metal stress and the stability of the system.

[0056] The test data of the three-dimensional remediation configuration methods for heavy metal contaminated soil constructed in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: Table 1 - Performance Test Data of Three-Dimensional Remediation Configuration Method for Heavy Metal Contaminated Soil Using Garden Plants

[0057] By comparing and analyzing the data in the table, it can be seen that the three-dimensional remediation configuration method of garden plants for heavy metal contaminated soil constructed in Examples 1-3 is superior to that constructed in Comparative Examples 1-4. This indicates that by selecting red-leaved glandular willow, chrysanthemum, and sunflower with different root depths to construct a three-layer configuration of trees, shrubs, and herbs, the deep-rooted trees fix and absorb cadmium in the deep soil, the middle-layer perennial flowers enrich and transport cadmium in the middle soil to the aboveground parts, and the shallow-rooted herbs enrich lead in the surface soil. The three work together to achieve layered remediation of the entire soil layer of contaminated soil, giving full play to the complementary advantages of different plants in root distribution, heavy metal accumulation capacity, and tolerance, improving the overall remediation efficiency, and solving the problem of difficult removal of deep heavy metals. By applying exogenous nitrogen fertilizer to enhance regulation based on a three-dimensional configuration, and applying urea in stages before and after planting, the nutrient requirements of plants at different growth stages can be supplied. Base fertilizer provides sufficient nitrogen source for early rooting and growth, while topdressing supplements nutrients during the rapid growth period, promoting the accumulation of plant biomass and root development, thereby enhancing the plant's ability to absorb and transport heavy metals and strengthening the remediation effect. Targeted harvesting and management of different plants at their appropriate growth stages—chrysanthemums are harvested after flowering, sunflowers are harvested whole after seed maturity, and red-leaved glandular willows are pruned after leaf fall—and the harvested materials are sent to a hazardous waste treatment center for high-temperature incineration and safe landfill, thereby removing heavy metals from the soil and reducing secondary pollution. At the same time, the crop rotation system of overwintering perennial chrysanthemums and perennial management of red-leaved glandular willows maintains the continuity and stability of the remediation community.

[0058] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for three-dimensional remediation of heavy metal contaminated soil using garden plants, characterized in that: Includes the following steps: Step 1: Site assessment and preparation. The heavy metal content of the contaminated soil to be remediated is tested to determine whether it is suitable for single Cd pollution, single Pb pollution, or Cd-Pb combined pollution. The Cd concentration range is 0.3-100 mg / kg, the Pb concentration range is 50-100 mg / kg, and the Cd-Pb combined pollution concentration range is Cd≤100 mg / kg and Pb≤100 mg / kg. The soil pH value is 5.5-7.

5. Step 2: Plant material selection. Select a combination of three layers of ornamental plants with different restorative functions: trees, shrubs and herbs. The trees are red-leaved glandular willows, the shrubs are small chrysanthemums 'Eastern Fence Little Mushroom', and the herbs are sunflowers. Step 3: Three-dimensional planting configuration. A three-dimensional configuration mode combining a three-layer vertical structure of trees-shrubs-herbs with horizontal staggered planting is adopted. The red-leaf willow, chrysanthemum and sunflower are planted according to the preset plant spacing and density. Step 4: Enhanced regulation of exogenous nitrogen. Apply nitrogen fertilizer in several applications before and after planting. The nitrogen fertilizer is urea. The total application rate is 260-300 mg N / kg soil, based on the weight of the topsoil layer of 0-20 cm. Step 5: Maintenance and harvesting. Regularly irrigate with nutrient solution and manage water. Harvest the above-ground parts of the plants at specific growth stages and collect the harvested materials for harmless treatment.

2. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step one, when the original soil to be repaired has poor physical and chemical properties, substrate improvement is carried out before planting. The substrate improvement formula is: the volume ratio of perlite, vermiculite and original soil is 0.8-1.2:0.8-1.2:1.8-2.2, or 10%-15% of well-rotted organic fertilizer is added to the original soil.

3. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step two, the red-leaved glandular willow is a deciduous tree with a root system depth of 1.5-2.0m, used for the fixation and absorption of Cd in deep soil; the chrysanthemum is a perennial flower of the Asteraceae family with a Cd translocation coefficient TF>1.0, used for the enrichment of Cd in the middle soil and its translocation to the aboveground parts; and the sunflower is an annual herb of the Asteraceae family with a single plant dry weight of 250g-350g, used for the enrichment of Pb in the surface soil.

4. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step three, the planting season is spring or autumn. Spring planting is from March to April when the soil temperature is 12℃-18℃, and autumn planting is from September to October when the soil temperature is 15℃-25℃. The soil moisture content is maintained at 60%-80% of field capacity during planting.

5. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step three, the vertical structure of the three-dimensional configuration mode is as follows: the upper layer is red willow with a plant height of 2.5-3.0m and a crown width of 1.0-1.2m; the middle layer is chrysanthemum with a plant height of 0.4-0.6m; and the lower layer is sunflower with a plant height of 1.5-2.0m.

6. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step three, the horizontal planting parameters are as follows: the spacing between plants of red-leaf glandular willow is 50cm, the row spacing is 50cm, and the density is 4 plants / m², using a plum blossom planting pattern, with hole dimensions of 40cm×40cm×40cm; the spacing between plants of chrysanthemum is 20cm, the row spacing is 20cm, and the density is 25 plants / m², interspersed among the red-leaf glandular willow plants, with a distance of 30cm from the main trunk of the willow; the spacing between plants of sunflower is 30cm, the row spacing is 30cm, and the density is 11 plants / m², planted on the periphery and in gaps, staggered by 10cm from the chrysanthemum.

7. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step four, the application schedule for urea is as follows: 40%-60% of the total amount is applied as base fertilizer before planting, and the remaining amount is applied as top dressing 20-40 days after planting; the application method is trench application or hole application, followed by covering with soil.

8. The method for three-dimensional remediation of heavy metal contaminated soil with garden plants according to claim 1, characterized in that: In step five, the nutrient solution is a modified Hoagland nutrient solution, the formula of which contains the following components at the following concentrations: calcium nitrate tetrahydrate 900-1000 mg / L, potassium nitrate 480-530 mg / L, magnesium sulfate heptahydrate 470-520 mg / L, potassium dihydrogen phosphate 130-140 mg / L, boric acid 2.5-3.0 mg / L, manganese sulfate tetrahydrate 2.0-2.3 mg / L, zinc sulfate heptahydrate 0.2-0.25 mg / L, copper sulfate pentahydrate 0.06-0.10 mg / L, ammonium molybdate tetrahydrate 0.01-0.03 mg / L, and sodium iron ethylenediaminetetraacetate 18-22 mg / L; the irrigation frequency is once every 5-9 days, 180-220 mL per plant each time.

9. The method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: In step five, the harvesting management includes: chrysanthemums are harvested from the ground in mid-to-late November after flowering, leaving a stubble height of 3-7cm; sunflowers are harvested from the whole plant in September-October after the seeds mature, with the flower heads and stems treated separately; red-leaved willows are pruned in December after leaf fall, retaining the main stem; the harvested materials are sent to a hazardous waste treatment center for high-temperature incineration or safe landfill.

10. A method for three-dimensional remediation of heavy metal contaminated soil using garden plants according to claim 1, characterized in that: Step five also includes crop rotation management, where the sunflowers are re-sown every year, the chrysanthemums can overwinter perennially, and the red-leaved glandular willows are managed as perennials; after 3-5 years of continuous restoration, the soil heavy metal content is tested, and once it meets the standards, it is transferred to regular garden maintenance.

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