Method for remediation of heavy metal contaminated soil based on sedum anagram grafting technology

Abstract

The application discloses a heavy metal contaminated soil remediation method based on a southeast sedum grafting technology. In order to solve the problem of slow remediation speed caused by slow growth and small aboveground biomass of the southeast sedum, the rootstock reserved after the aboveground part of the southeast sedum is removed is used as a stock, and the new bud leaves of the feicao or the eight treasure sedum are used as scions, so that the grafted plants are formed through the grafting technology and are planted in the heavy metal contaminated soil, and the grafted plants utilize the root system of the southeast sedum to carry out phytoremediation on the heavy metals in the soil. After the grafted plants are planted in the contaminated soil, the Cd, Pb and Zn extraction amount of the southeast sedum can be improved, the extraction speed can be accelerated, and the remediation time can be shortened. In addition, the method is also helpful to improve the soil microbial diversity and stimulate more microbial groups participating in nutrient circulation and mutual symbiosis with plants. It can be seen through comprehensive comparison that the application can greatly shorten the plant extraction time, is helpful to soil health and has great application potential.

Description

Technical Field

[0001] This invention relates to the field of heavy metal contaminated farmland soil remediation technology, and more specifically to a method for remediating heavy metal contaminated soil based on Sedum sarmentosum grafting technology. Background Technology

[0002] Human activities such as mining, metallurgy, manufacturing, fertilization, and irrigation are causing heavy metal pollution in soils, including Cd, Pb, Cr, Hg, As, and Zn. Excessive amounts of these elements in the soil not only inhibit plant growth and development and reduce crop yields, but their accumulation in edible plant parts can also be passed on to humans through the food chain, threatening human health. Many remediation technologies have been developed to address the pressing problem of heavy metal pollution in soils, such as passivation, leaching, soil replacement, and electroremediation. However, these methods also face many challenges, including: potential secondary pollution and release; huge energy consumption; high equipment and maintenance costs; and damage to soil properties and impact on the long-term use of arable land.

[0003] Phytoremediation, a remediation technology that leverages the ability of some plants to accumulate large amounts of heavy metals absorbed from contaminated soil in their above-ground parts, is gaining attention as a method that does not damage soil fertility and productivity and requires no special equipment or energy. Currently, over 400 plant species have been identified that can be used for heavy metal extraction. Among them, *Sedum aizoon*, with its roots' specific simultaneous absorption of Cd, Pb, and Zn, is being widely applied in environments with complex pollution. However, the low biomass and slow growth rate of *Sedum aizoon* severely limit its soil remediation speed, becoming the most significant challenge in phytoremediation.

[0004] Grafting is an asexual reproduction technique that involves attaching a bud or branch from one plant to another. As an agronomical measure to improve stress resistance, increase yield and quality, and overcome continuous cropping obstacles, grafting has a history of over a thousand years. *Sedum aizoon* is a plant in the Crassulaceae family, which consists mostly of perennial succulent herbs and is relatively easy to graft. Unlike *Sedum aizoon*, many plants in the Crassulaceae family also possess large biomass and rapid growth rates. However, there is currently no existing technology to improve the heavy metal remediation capacity of *Sedum aizoon* through grafting. Summary of the Invention

[0005] The purpose of this invention is to combine the ability of Sedum sarmentosum roots to absorb heavy metals with the large biomass of other above-ground parts of plants, and to provide a method for remediating heavy metal contaminated soil based on Sedum sarmentosum grafting technology.

[0006] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0007] A method for remediating heavy metal contaminated soil based on grafting technology of Sedum aizoon is proposed. The method is as follows: the rhizome of Sedum aizoon after removing the above-ground parts is used as the rootstock, and the new shoots and leaves of Sedum spectabile or Sedum truncatum are used as scions. Grafting technology is used to form grafted plants, which are then planted in heavy metal contaminated soil. The grafted plants use the root system of Sedum aizoon to perform phytoremediation of heavy metals in the soil.

[0008] Preferably, the grafting technique used is the cleft grafting method.

[0009] Preferably, the method for forming grafted plants through grafting technology is as follows:

[0010] Cultivate a batch of Sedum aizoon by cuttings, then cut off the above-ground part of the Sedum aizoon plant, leaving a section of stem and all roots as rootstock. Make a double-sided wedge-shaped cut at the top of the rootstock. Take new shoots and leaves from Sedum spectabile or Sedum truncatum as scions, and cut the lower end of the scion into a double-sided wedge-shaped tip. Insert the tip of the scion tightly into the cut of the rootstock and wrap it with grafting tape. Transfer it to nutrient solution for cultivation until it survives.

[0011] Preferably, the grafting tape is made of glutinous rice paper.

[0012] As a preferred method, when propagating Sedum semperflorens by cuttings, take 4-6 cm long new shoots from the Sedum semperflorens plant, retaining 2-3 leaves, and cultivate them in water and nutrient solution to grow plants required for processing rootstock.

[0013] Preferably, the length of the new shoots used as scions is 4–6 cm.

[0014] Preferably, the tip of the scion and the length of the split in the rootstock are 4 to 6 mm.

[0015] Preferably, the heavy metal in the soil contaminated with heavy metals is cadmium-contaminated soil, and the scion is preferably the new shoots and leaves of *Sedum aizoon*.

[0016] Preferably, the heavy metal in the soil contaminated with heavy metals is lead-contaminated soil, and the scion is preferably the new shoots and leaves of *Sedum aizoon*.

[0017] Preferably, the heavy metal in the soil contaminated with heavy metals is zinc-contaminated soil, and the scion is preferably a new shoot or leaf of Sedum spectabile.

[0018] Compared with existing technologies, this invention has the following advantages: Current physical and chemical methods for remediating heavy metal pollution may generate secondary pollution and releases, the remediation process involves huge energy consumption, requires high equipment and maintenance costs, and may damage soil properties and affect the long-term use of arable land. Traditional plant extraction, due to its small aboveground biomass, is too slow, requiring decades or even centuries to remediate, thus occupying arable land for a long time. The grafting remediation technology provided by this invention has the following advantages: First, the aboveground parts of the plant grow rapidly and have a large biomass, which will greatly shorten the plant extraction time. Second, the method of this invention can achieve simultaneous remediation of Cd, Pb, and Zn by *Sedum aizoon*, and the scion can be selected according to different types of heavy metal pollution to improve remediation efficiency. Third, this technology can also activate the growth and metabolism of soil microorganisms, nutrient absorption, and heavy metal detoxification functions, contributing to soil health. Attached Figure Description

[0019] Figure 1 The optimal scion selection is based on a comprehensive consideration of price, fresh weight, growth rate, and graft survival rate;

[0020] Figure 2 The growth of Sedum aizoon, grafted Sedum sarmentosum and Sedum spectabile after 21 days in polluted soil;

[0021] Figure 3 The extraction yield, extraction rate, and estimated remediation time required to reach national standards for cadmium from the three plants;

[0022] Figure 4 The lead extraction yield, extraction rate, and estimated remediation time required to reach national standards for the three plants were determined.

[0023] Figure 5 The zinc extraction yield, extraction rate, and estimated remediation time required to reach national standards for the three plants were determined.

[0024] Figure 6 The effects of different treatments on soil microorganisms. Detailed Implementation

[0025] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0026] In the following examples, the Crassulaceae plants used were commercially available common varieties and were not unique. The paddy soil used in Examples 2-4 was collected from paddy soil contaminated with multiple heavy metals near the Yinkuangshan site in Shangyu City, Zhejiang Province (29.99° latitude, 120.78° longitude). Referring to the Chinese Standard for Risk Control of Agricultural Land Soil Pollution (GB 15618—2018), the soil showed excessive levels of Cd, Pb, and Zn, specifically: Cd content was 0.46 mg / kg (risk screening value 0.4 mg / kg), Pb content was 334.22 mg / kg (risk screening value 100 mg / kg), and Zn content was 211.8 mg / kg (risk screening value 200 mg / kg). All other reagents and materials used were commercially available unless otherwise specified.

[0027] Example 1

[0028] In this embodiment, considering factors such as price, growth rate, and grafting survival rate, scions suitable for grafting with the root system of Sedum aizoon were selected from other Crassulaceae plants.

[0029] This embodiment purchased five common Crassulaceae plants, including Sedum alfredii, Sedum lineare, Sedum aizoon, Sedum spectabile, and Kalanchoe blossfeldiana, and recorded the prices of each plant from three vendors. Upon receiving the seedlings, the initial fresh weight of each plant was recorded, with three replicates for each plant type. They were planted in potting soil, watered to maintain approximately 70% humidity, and grown in an artificial climate chamber for 14 days (26°C, 65% humidity, 16h / d light). The plants were then removed from the potting soil, and their fresh weight was measured. The growth rate of each plant was calculated using the following formula:

[0030] Growth rate = (14-day fresh weight - initial fresh weight) / 14

[0031] Except for *Sedum aizoon*, 5cm long new shoots of four other plants were cut as scions. In this embodiment, another batch of *Sedum aizoon* was prepared in advance using cuttings and used as rootstock. The specific steps were as follows: 60 new shoots, approximately 5cm long, were cut from healthy *Sedum aizoon* stems using scissors. Each plant retained 2-3 leaves and was air-dried for 12 hours. Then, all plants were placed in deionized water and cultured in the dark for 7 days (26℃, 65% humidity). Afterward, the deionized water was replaced with 1 / 4 Hoagland solution, and the plants were cultured under 16h / d light for 14 days. *Sedum aizoon* of uniform size were selected, the above-ground parts were cut off, and a small section of stem and all roots were retained as rootstock. This embodiment uses cleft grafting. First, a 5mm long cleft was cut vertically downwards from the center of the rootstock tip, and the lower end of the scion was cut into a 5mm long double-sided wedge shape. Then, the double-wedge surfaces of the scion were inserted into the cleft of the rootstock, ensuring a tight fit between the two cuts, and wrapped with rice paper. Four grafted plants were grouped together, with three groups of each type of plant. They were cultured in 1 / 4 Hogland nutrient solution for 7 days (in the dark for the first 3 days, and then under 16 hours of light per day starting from the 4th day), and the survival rate was then recorded.

[0032] Ultimately, *Sedum spectabile* and *Sedum morganianum* were determined to be the optimal scions for grafting and plant restoration. Among common Crassulaceae plants, the most expensive is *Kalanchoe blossfeldiana*, priced at 2.6 yuan per unit, followed by *Sedum aizoon* (2.2 yuan) and *Sedum spectabile* (1.1 yuan). *Sedum lineare* and *Sedum spectabile* are the cheapest, both priced below 1 yuan per unit. Figure 1 (a)). The fresh weight of the plants was highest at the initial stage and after 14 days of growth, followed by *Sedum spectabile* and *Sedum morganianum*. *Sedum aizoon* and *Sedum lineare* had the lowest fresh weight. Figure 1 (b)). Growth rates were similar, with Kalanchoe and Sedum being the fastest, exceeding 0.5 g / day. Sedum spectabile also showed a significantly higher growth rate than Sedum aizoon and Sedum lineare, reaching 0.37 g / day. Figure 1 (c)). Furthermore, the survival rate of *Sedum spectabile* and *Sedum morganianum* grafted onto *Sedum aizoon* was greater than 80%, significantly higher than the other two plants (c). Figure 1 (d) In general, Sedum lineare is a commonly used landscaping plant, extremely vigorous and inexpensive. However, its small biomass, slow growth rate, and low grafting survival rate make it unsuitable for plant extraction. Kalanchoe blossfeldiana has beautiful flowers, a large biomass, and a fast growth rate. Because its Chinese name symbolizes longevity, it is often used as an indoor potted plant. However, its growing conditions are demanding and it is not suitable for outdoor cultivation. Furthermore, its high price and low grafting survival rate also make it unsuitable for plant extraction. Sedum spectabile and Sedum spectabile are common landscaping plants, inexpensive, with a relatively large biomass and fast growth rate, especially with a high grafting survival rate. Therefore, these two plants were selected as scions for grafting and soil remediation in subsequent experiments.

[0033] Example 2

[0034] In this embodiment, the remediation effect of grafting Sedum aizoon on cadmium-contaminated soil was tested.

[0035] Paddy soil contaminated with heavy metals was collected from near the silver mine in Shangyu City, Zhejiang Province (29.99° latitude, 120.78° longitude) at a depth of 0–20 cm. After natural air drying, the soil was thoroughly mixed, discarding gravel, dead rice twigs, etc., and then ground and sieved through a 10-mesh sieve. The soil pH was determined to be 6.4. 0.2 g of dry soil was weighed and microwave-digested using 4 ml HNO3, 2 ml H2O2, and 1 ml HF. After making up to volume with boric acid to remove residual HF, the Cd concentration was determined using ICP-OES. Referring to the Chinese Standard for Risk Management of Agricultural Land Soil Pollution (GB 15618—2018), the Cd content in this soil exceeded the standard, at 0.46 mg / kg (risk screening value is 0.4 mg / kg).

[0036] Based on the results of the previous step, *Sedum spectabile* and *Sedum spectabile* were ultimately selected as scions. In this embodiment, the grafted plants were planted in contaminated soil, with each pot containing 1 kg of dry soil and one plant. Three replicates were set up for each type of scion. Additionally, three *Sedum aizoon* cuttings obtained in the previous step were planted in three pots of contaminated soil as a control group. All experimental and control groups were then thoroughly watered and grown in a culture room, receiving 100 ml of water every 7 days. After 21 days, the plants were collected, and the roots were washed with deionized water and EDTA. Bud length and fresh bud weight were measured after photographing. The aboveground parts and roots of the plants were dried and weighed, and then microwave digested using 4 ml HNO3, 2 ml H2O2, and 1 ml HF. After adjusting the volume with boric acid to remove residual HF, the Cd concentration was determined using ICP-OES. The Cd concentration of the aboveground parts of each plant was calculated. The heavy metal extraction amount per pot is expressed as the total Cd content of the aboveground parts. The extraction rate of heavy metals per unit weight of contaminated soil by different plants and the estimated remediation time are calculated using the following formula:

[0037] Extraction speed = Extraction volume / Time

[0038] Estimated repair time = (Measured value - National standard screening value) / Extraction speed

[0039] The results showed that although *Sedum spectabile* and *Sedum morganianum* used for soil remediation still utilized the root system of *Sedum aizoon*, the three plants still exhibited significant differences after 21 days of remediation. Figure 2 (a) The fresh weight of *Sedum aizoon* reached 24.9g, and the fresh weight of *Sedum spectabile* also reached 16.6g, significantly higher than the 10.6g of *Sedum aizoon*. Figure 2 (b) The plant height of both *Sedum spectabile* and *Sedum morganianum* was greater than 15cm, significantly higher than that of *Sedum aizoon* (6.4cm). Figure 2(c) Compared with Sedum spectabile, grafting Sedum spectabile increased the Cd concentration in the aboveground parts, reaching 37.5 μg / g. Figure 3 (a)). Grafting *Sedum aizoon* had little effect on the Cd concentration in the aboveground parts. Furthermore, the extraction amount and rate of heavy metals from grafted plants were significantly increased. *Sedum aizoon* showed the highest Cd extraction amount and rate, at 124.7 μg and 5.9 μg / day (a). Figure 3 (b), (c)). Compared with physical and chemical methods, phytoremediation is always a concern due to its longer time requirement. To achieve the goal of reducing the heavy metal concentration in contaminated soil to below the national standard screening value (Cd reduction of 60 μg / kg), *Scutellaria baicalensis* requires the shortest time, 5 days. Figure 3 (d)

[0040] Example 3

[0041] In this embodiment, the effect of grafting Sedum aizoon on the remediation of lead pollution in soil was investigated.

[0042] Heavy metal contaminated paddy soil collected from near the silver mine in Shangyu City, Zhejiang Province (29.99° latitude, 120.78° longitude) was found to contain 334.22 mg / kg of phosphorus (Pb) after negative testing. According to the Chinese Standard for Risk Management of Agricultural Land Soil Pollution (GB15618—2018), the Pb content in this soil is severely exceeded (risk screening value is 100 mg / kg). *Sedum spectabile* and *Sedum spectabile* were selected as scions. In this embodiment, the grafted plants were planted in contaminated soil. Each pot contained 1 kg of dry soil and one plant. Three replicates were set up for each type of scion. Three *Sedum aizoon* cuttings obtained in the previous step were planted in three pots of contaminated soil as a control group. All experimental and control groups were then thoroughly watered and grown in a culture room, receiving 100 ml of water every 7 days. After 21 days, the plants were collected, and the roots were washed with deionized water and EDTA. After drying and weighing the aboveground parts and roots of the plants, microwave digestion was performed using 4 ml HNO3, 2 ml H2O2, and 1 ml HF. After adjusting the volume with boric acid to remove residual HF, the Pb concentration was determined using ICP-OES. The Pb concentration of each plant's aboveground parts was calculated. The heavy metal extraction amount per pot is expressed as the total Pb content of the aboveground parts. The heavy metal extraction rate per unit weight of contaminated soil for different plants and the estimated remediation time were calculated using the following formula:

[0043] Extraction speed = Extraction volume / Time Estimated repair time = (Measured value - National standard screening value) / Extraction speed

[0044] The results showed that the Pb concentration in the aboveground parts of grafted *Sedum aizoon* decreased compared to *Sedum sarmentosum*, but due to the increased plant weight, the Pb extraction amount was still significantly higher than that of *Sedum sarmentosum*, at 965 μg, which was significantly higher than the 513 μg of *Sedum sarmentosum*. Figure 4(a), (b)). Grafting *Sedum spectabile* had no significant effect on the Pb concentration in the aboveground parts, but the total extraction amount increased to 733 μg due to the increased weight. Grafted *Sedum aizoon* showed the fastest repair rate at 46 μg / day, followed by grafted *Sedum spectabile* at 35 μg / day, both significantly higher than *Sedum aizoon*'s 24 μg / day. Figure 4 (c)). To achieve the goal of reducing the heavy metal concentration in contaminated soil to below the national standard screening value (Pb reduction of 234,220 μg / kg), *Sedum aizoon* requires a remediation time of up to 26 years. Grafting *Cephalotaxus fortunei* will significantly shorten the remediation time to 14 years. Figure 4 (d)

[0045] Example 4

[0046] In this embodiment, the effect of grafting Sedum aizoon on the remediation of zinc pollution in soil was investigated.

[0047] The Zn content of paddy soil contaminated with heavy metals, collected from near the silver mine in Shangyu City, Zhejiang Province (29.99° latitude, 120.78° longitude), was measured to be 211.8 mg / kg after negative testing. Referring to the Chinese Standard for Risk Management of Agricultural Land Soil Pollution (GB15618—2018), the Zn content in this soil exceeded the standard (risk screening value of 200 mg / kg). *Sedum spectabile* and *Sedum spectabile* were selected as scions. In this embodiment, the grafted plants were planted in the contaminated soil. Each pot contained 1 kg of dry soil and one plant. Three replicates were set up for each type of scion. Three *Sedum aizoon* cuttings obtained in the previous step were planted in three pots of contaminated soil as a control group. The experimental groups and control groups were then thoroughly watered and grown in a culture room, with 100 ml of water given every 7 days. After 21 days, the plants were collected, and the roots were washed with deionized water and EDTA. After drying and weighing the aboveground parts and roots of the plants, microwave digestion was performed using 4 ml HNO3, 2 ml H2O2, and 1 ml HF. After adjusting the volume with boric acid to remove residual HF, the Zn concentration was determined using ICP-OES. The Zn concentration of each plant's aboveground parts was calculated. The heavy metal extraction amount per pot was expressed as the total Pb content of the aboveground parts. The heavy metal extraction rate per unit weight of contaminated soil for different plants and the estimated remediation time were calculated using the following formula:

[0048] Extraction speed = Extraction volume / Time Estimated repair time = (Measured value - National standard screening value) / Extraction speed

[0049] The results showed that the Zn concentration in the aboveground parts of *Sedum aizoon* decreased compared to *Sedum sarmentosum*, but due to the increased plant weight, the Zn extraction amount was still significantly higher than that of *Sedum sarmentosum*, at 1809 μg, which was significantly higher than the 1455 μg of *Sedum sarmentosum*. Figure 5(a), (b)). Grafting *Sedum spectabile* had no significant effect on the Pb concentration in the aboveground parts, but the total extraction yield increased to 1986 μg due to the increased weight. Grafted *Sedum spectabile* showed the fastest repair rate at 95 μg / day, followed by grafted *Sedum aizoon* at 86 μg / day, both significantly higher than *Sedum aizoon*'s 69 μg / day. Figure 5 (c)). To achieve the goal of reducing the heavy metal concentration in contaminated soil to below the national standard screening value (Pb reduction of 11800 μg / kg), *Sedum aizoon* requires a remediation time of up to 171 days. Grafted *Sedum spectabile* and *Sedum truncatum* significantly shorten the remediation time to 137 and 125 days, respectively. Figure 5 (d)

[0050] It should be noted that Examples 2 to 4 above explored the performance of grafted plants in the remediation of different heavy metals, but the specific experiments in the three examples were carried out together, and the plants and soil used were the same. The only difference was the focus on different heavy metals in the final test indicators.

[0051] Example 5

[0052] In this embodiment, the effects of grafting techniques on Sedum aizoon on the structure and function of soil microbial communities were investigated.

[0053] In this embodiment, DNA samples were extracted from soil near the roots of each plant and from soil without plant growth using a DNA isolation kit from Examples 2–4. The concentration and purity of the extracted DNA were analyzed using a NanoDrop ND-1000 UV-Vis spectrophotometer and 1% agarose gel electrophoresis. The V4–V5 region of the bacterial 16S rRNA gene was amplified using primer pairs 308F (5′-GTGCAGCMGCGCGGTAA-3′) and 806R (5′-CCTCAATTCMTTRAGTT-3′). High-throughput sequencing was performed on the Illumina Nova 6000 platform for the 16S rRNA gene from Majorbio Bio-Pharm Technology Co., Ltd. Quality control and sequence processing were then performed using Fastp and QIIME2. Operational taxonomic units (OTUs) and representative sequences were generated using the default UPARSE pipeline. The SILVA database was used as a reference for taxonomic annotation. R was used for alpha diversity analysis, including richness and Shannon index. The effects of different treatments on bacterial β-diversity were analyzed using principal coordinate analysis (PCoA) based on the Bray-Curtis distance matrix and nonmetric multidimensional scaling (NMDS). In addition, linear discriminant analysis of effect size (LEfSe) was performed.

[0054] exist Figure 6In the following representation, Ck represents unrestored soil, S represents *Sedum aizoon*, P represents *Sedum spectabile*, and H represents *Sedum spectabile*. The results showed that group Ck had the fewest OTUs (1497), group P had the most OTUs (2090), and groups S, P, and H all contained 1043 OTUs. Figure 6 (a) Compared with the control (CK), plant extracts increased the richness and α-diversity index of soil microorganisms (e.g., Shannon). Figure 6 (b)). Furthermore, the β-diversity of the three microbial communities also differed significantly from that of Ck. PCoA analysis revealed distinct clustering of plant extracts and Ck in different regions ( Figure 6 (c)). Notably, the microbial communities of S, P, and H are close to each other, indicating similarity. Conversely, the separation of Ck from the three plants along the first (91.6%) and second (5.6%) principal axes indicates differences in the microbial communities. Furthermore, NMDS analysis ( Figure 6 (c) also indicates that the Bray-Curtis distance among the three plant species was relatively small. Overall, plant extraction enhanced α-diversity of the soil microbial community and had a significant impact on β-diversity. Figure 6 (d) shows different microorganisms in the soil, with LDA scores exceeding 4. The dominant microbial groups in the unremediated soil were mainly Firmicutes and Bacillus. These two types of microorganisms can produce spores and are highly resistant to environmental stress, but they lack competitiveness in uncontaminated environments. Therefore, the decrease in the abundance of these two types of microorganisms after phytoremediation also indicates that the rhizosphere microenvironment of the contaminated soil was improved after remediation. Furthermore, the planting of these three plants stimulated more microbial groups in the soil, including those involved in nutrient cycling and mutualistic symbiosis with plants, such as Acidobacteriota, Proteobacteria, Actinobacteria, Planctomycetota, and Asticcacaulis. The core bacterial groups Sphingomonadales and Burkholderiales, previously reported as closely related to cadmium accumulation in Sedum aizoon, were also found here. They can utilize carbon sources secreted by plant roots and promote plant growth and heavy metal accumulation. Therefore, phytoremediation is beneficial in promoting soil nutrient cycling and maintaining soil health.

[0055] The embodiments described above are merely some preferred implementations of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for remediation of heavy metal contaminated soil based on the grafting technology of Sedum alfredii H., characterized in that, The rootstock reserved after removing the above-ground part of Sedum southeast is used as a stock, and the new bud leaves of Sedum lineare or Sedum spectabile are used as scions to form grafted plants by grafting technology and plant in heavy metal contaminated soil, and the grafted plants use the root system of Sedum southeast to repair the heavy metals in the soil by plants; The method for forming the grafted plants by grafting technology is: A batch of Sedum southeast is cultivated by cutting, and then the above-ground part of the Sedum southeast plant is cut off, and a section of stem and all roots are reserved as a stock, and a double-wedge-shaped split is formed at the top end of the stock; the new bud leaves of Sedum lineare or Sedum spectabile are cut as scions, and the lower end of the scions is cut into a double-wedge-shaped tip; the tip of the scion is tightly inserted into the split of the stock and wrapped with a grafting tape, and then transferred to a nutrient solution for cultivation until survival; The heavy metal contaminated soil is cadmium contaminated soil, and the scion is the new bud leaf of Sedum lineare; Alternatively, the heavy metal contaminated soil is lead contaminated soil, and the scion is the new bud leaf of Sedum lineare; Alternatively, the heavy metal contaminated soil is zinc contaminated soil, and the scion is the new bud leaf of Sedum spectabile.

2. The method for remediation of heavy metal contaminated soil based on the grafting technique of Sedum angustifolium according to claim 1, characterized in that, The grafting tape is made of glutinous rice paper.

3. The method for remediation of heavy metal contaminated soil based on the grafting technique of Sedum angustifolium according to claim 1, characterized in that, When the Sedum southeast is cultivated by cutting, the new bud leaves of 4-6 cm in length and 2-3 leaf blades are cut from the Sedum southeast plant, and then cultivated in water and nutrient solution to form the plants required for processing the stock.

4. The method for remediation of heavy metal contaminated soil based on the grafting technique of Sedum angustifolium according to claim 1, wherein, The length of the new bud leaves used as the scions is 4-6 cm.

5. The method for remediation of heavy metal contaminated soil based on the grafting technology of Sedum angustifolium according to claim 1, wherein, The length of the tip of the scion and the split of the stock is 4-6 mm.

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