Remediation method for cadmium-polluted soil

Abstract

The invention discloses a cadmium-contaminated soil remediation method which comprises the following steps: performing seedling vernalization prevention treatment on sedum plumbizincicola branches to obtain sedum plumbizincicola seedlings; then the sedum plumbizincicola seedlings are transplanted into the cadmium-contaminated soil, in the planting and growing period of the sedum plumbizincicola seedlings, the environment temperature is controlled to range from 8 DEG C to 25 DEG C, and field management is conducted regularly; and when the branches of the sedum plumbizincicola do not grow obviously within 15-20 days, harvesting the sedum plumbizincicola, and removing the harvested object from the field. According to the method, through anti-vernalization treatment and planting of the sedum plumbizincicola, the phenomenon that most plants die after flowering due to low-temperature vernalization of the sedum plumbizincicola can be avoided, so that the vegetative growth cycle of the sedum plumbizincicola is effectively prolonged, and then the absorption and remediation efficiency of cadmium in the cadmium-contaminated soil is improved.

Description

Technical Field

[0001] The invention relates to the technical field of soil regeneration, and in particular to a method for repairing cadmium-contaminated soil. Background Art

[0002] Sedum sedum Sedum plumbizincicola XH Guo et SB Zhou ex LH Wu) is a new species of the genus Sedum in the Crassulaceae family. It is perennial, has a large biomass, and is easy to harvest. It is a hyperaccumulator of heavy metals cadmium (Cd) and zinc (Zn), and can effectively remove Cd and Zn from contaminated soil. The enrichment coefficient of Sedum serrata for Cd (the ratio of the aboveground concentration of the plant to the soil concentration) can reach more than 100, making it an important plant resource for the remediation of Cd-contaminated farmland soil. Over the past decade, Sedum serrata has achieved good practical results in the remediation of Cd-contaminated farmland soil and has broad application prospects. However, in the process of promotion and application, after experiencing low-temperature vernalization in winter and flowering and seeding in summer, most of the branches of Sedum serrata will die and the remaining parts will grow slowly. This phenomenon has an important impact on its subsequent large-scale planting and efficient absorption and remediation of heavy metals in the soil, and is an urgent problem to be solved.

[0003] Vernalization refers to the process in which winter plants switch from vegetative growth to reproductive growth after experiencing low temperatures, and eventually induce the plants to flower. Vernalization can cause non-flowering plants to bloom or bloom early, which is of great significance to agricultural production. Vernalization technology has been applied to various vegetables, flowers and medicinal materials, such as Wutacai ( Brassica narinosa ),broad bean( Vicia faba ),lily( Lilium brownii )、Danggui( Angelica sinensis ) and other crops, and achieved good results. However, different species have different requirements for vernalization conditions due to their different growth environments and states. Therefore, studying the conditions required for vernalization of the Cd hyperaccumulator Sedum serrata and its response to low temperatures in the growth environment will help Sedum serrata avoid vernalization, promote vegetative growth, and improve its efficiency in plant absorption and repair of Cd in contaminated soils.

[0004] Low temperature vernalization can cause changes in physiological indicators such as nucleic acid metabolism, endogenous hormone metabolism, and carbon-nitrogen metabolism in plants. The nitrogen-carbon ratio (C / N) is considered to be the main determinant of the flowering process of plants. Carbohydrates not only provide energy for the physiological metabolic process of flowering, but also directly participate in the physiological response of flowering. A higher soluble sugar content helps the development of flower stems, making them easier to bolt; protein plays an important role in cell life activities and is an important material basis for flowering. By measuring the changes in soluble sugar, starch, soluble protein, and total nitrogen content, the changes in the C / N ratio can be deduced; the higher the C / N ratio, the greater the possibility of bolting and flowering of the plant.

[0005] Although many studies have revealed the importance of vernalization in plants, there has been no systematic study on the low-temperature vernalization of the cadmium and zinc hyperaccumulator Sedum serrata, and the critical temperature and duration of vernalization are still unclear. Therefore, a method is needed to improve the remediation effect of cadmium-contaminated soil by anti-vernalization treatment of Sedum serrata to solve the above problems. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for repairing cadmium-contaminated soil.

[0007] The technical solution of the present invention is: a method for repairing cadmium-contaminated soil, comprising the following steps: Step 1, performing anti-vernalization treatment on the branches of Sedum serrata to obtain Sedum serrata seedlings; wherein the anti-vernalization treatment is: raising the branches of Sedum serrata in a temperature environment of 8-25°C for 30-90 days; Step 2: subsequently transplanting the Sedum sedum seedlings into cadmium-contaminated soil, controlling the ambient temperature at 8-30° C. during the planting and growth of the Sedum sedum seedlings, and performing field management regularly; Step 3: When the branches of the Sedum serrata show no obvious growth within 15 to 20 days, harvest the Sedum serrata and remove the harvest from the field.

[0008] Further, in step 2, the Sedum serrata seedlings are transplanted at a planting density of 12~25cm×12~25cm.

[0009] Description: Appropriate planting density can ensure that there is enough space and light between the plants of Sedum sutchuenensis, promote photosynthesis and gas exchange, and is conducive to the healthy growth of the plants. Properly increasing the planting density can shorten its growth cycle. At the same time, good ventilation conditions can also help reduce the occurrence of pests and diseases. Reasonable planting density can avoid excessive competition between plants and ensure that each Sedum sutchuenensis plant can obtain sufficient nutrients and water to meet its growth and development needs. In addition, the appropriate planting density can promote the growth of the aboveground part of Sedum sutchuenensis and increase its biomass, so that there are more leaves and branches to absorb heavy metals in the soil. By controlling the planting density, the growth and heavy metal absorption of Sedum sutchuenensis can be optimized, thereby shortening the time limit for remediation of contaminated soil and controlling the remediation cost. In addition, the appropriate planting density can also ensure that Sedum sutchuenensis absorbs heavy metals in the soil evenly, avoiding local excessive or insufficient absorption, and improving the quality and efficiency of remediation.

[0010] Furthermore, in step 2, the field management includes irrigation, drainage, topdressing, insecticide and weeding.

[0011] Description: Irrigation and drainage are properly adjusted according to crop needs and soil conditions to provide crops with suitable moisture conditions; weeding can prevent weeds from competing with crops for nutrients, water and light, creating a better growth environment for crops; fertilization is reasonably supplemented according to crop needs and soil nutrient conditions to ensure that crops obtain sufficient nutrition; Biological control, chemical control or agricultural control can be used to reduce the harm of pests and diseases to crops, and pest and disease problems can be discovered and dealt with in a timely manner to prevent their spread and proliferation; through routine field management of Sedum truncatum, the growth and cadmium accumulation and enrichment of Sedum truncatum can be improved, the growth environment of Sedum truncatum can be optimized, and the growth of Sedum truncatum can be promoted.

[0012] Furthermore, in step 2, when the ambient temperature is lower than 8°C, the ambient temperature of the Sedum serrata seedlings is controlled to be between 8-30°C by means of covering with film, greenhouse or configuring heating equipment; when the ambient temperature is higher than 30°C, the ambient temperature of the Sedum serrata seedlings is controlled to be between 8-30°C by means of building a shade net or configuring cooling equipment.

[0013] Note: Through ground film covering, greenhouses or heating equipment, the soil or air temperature can be increased, so that it can effectively absorb and preserve solar radiation energy, and convert it into heat energy to transfer or affect the soil, thereby increasing the soil environment temperature. At the same time, this is also a common way to control the ambient temperature in plant cultivation. It is economical and the technology is mature. Building a shade net can effectively prevent the transmission of solar radiation energy to the surface, and configuring cooling equipment is also a common way to effectively reduce the ambient temperature. It is also an economical and mature means to reduce the surface temperature under high temperature climate conditions.

[0014] Further, in step 2, before the Sedum sedum seedlings are transplanted into the cadmium-contaminated soil, the cadmium-contaminated soil is tilled and fertilized, and the tillage and fertilization method is: Fermented agricultural waste was applied to cadmium-contaminated soil at a rate of 800-1500 kg / mu, followed by tillage.

[0015] Description: Through the landfill and tillage of fermented agricultural waste, on the one hand, agricultural waste can be utilized as a resource, and on the other hand, the soil can be fertilized and improved to promote the growth of Sedum serrata seedlings.

[0016] Furthermore, the agricultural waste fermentation product is obtained by fermenting agricultural waste, and the agricultural waste is crops grown in local non-polluted areas, selected from rice straw or corn straw.

[0017] Note: Corn straw is often used as agricultural waste after crops are planted in the north, while rice straw is often used as agricultural waste after crops are planted in the south. The corresponding selection can be made according to local production conditions. By reusing these agricultural wastes, on the one hand, the problem of agricultural waste disposal can be avoided, and on the other hand, resources can be utilized to prepare a nutrient matrix that promotes the growth of Sedum serrata.

[0018] Furthermore, the fermentation method of the agricultural waste fermentation product is: 1) Build a fermentation frame with a height of 4-6m, a width of 2-3m, and a length of 2-3m. Cut the agricultural waste into pieces of 3-5cm and spread them in layers in the fermentation frame. The thickness of each layer of agricultural waste is 20-30cm. 2) After each layer of agricultural waste is filled, water at 10-15°C is sprayed on each layer of agricultural waste to keep the moisture content of the agricultural waste at 40-50%, and then the composite bacterial slurry is evenly sprayed. The spraying thickness of the composite bacterial slurry is 2-5 cm. 3) After the agricultural waste is spread in layers, it is fermented for 3-5 days to obtain the fermented agricultural waste.

[0019] Description: The fermentation method can produce agricultural waste fermentation products with stable performance, so that in the subsequent landfill and tillage of the agricultural waste fermentation products, the soil temperature can be effectively controlled to reach the anti-vernalization temperature range of Sedum serrata, thereby preventing the vernalization phenomenon of Sedum serrata. By spraying water below normal temperature on agricultural waste to keep its moisture content at this humidity, the fermentation rate can be controlled. On the premise of maintaining the stability of each bacteria in the composite slurry, the fermented agricultural waste can play a better role in the subsequent landfill and tillage, thereby controlling soil temperature and maintaining soil fertility.

[0020] Furthermore, the composite bacterial slurry is obtained by mixing the composite bacterial material and water in a mass ratio of 20-30:7; The composite bacterial feed is composed of 40-50 parts of Bacillus polymyxa, 5-10 parts of Bacillus subtilis, 2-7 parts of Enterococcus faecalis, 150-300 parts of straw powder, 50-80 parts of urea and 10-40 parts of superphosphate by weight; The straw powder is a powder obtained by ball-grinding rice straw or corn straw through a 50-100 mesh sieve.

[0021] Description: The composite bacterial material with the above ratio can effectively improve the use effect of agricultural waste fermentation products. Bacillus polymyxa has a broad spectrum of antagonistic activity and can effectively prevent the occurrence of various plant fungi, bacteria and nematodes. Bacillus polymyxa can also produce substances such as plant hormones to promote plant growth and development, increase crop yields, and produce a variety of enzymes such as cellulase; Bacillus subtilis can secrete a variety of active substances, such as subtilisin, nystatin, gramicidin, etc., which have a broad spectrum of antibacterial effects; and Enterococcus faecalis can form a symbiotic relationship with plant roots, secrete growth hormones and beneficial metabolites, and promote plant growth by increasing plant nutrient absorption and improving stress resistance. This helps to increase crop yield and tolerance. Enterococcus faecalis can also produce digestive enzymes to decompose polysaccharides, cellulose and other substances that are difficult for plants to digest and absorb, releasing more nutrients for plants to absorb and utilize.

[0022] Furthermore, ultrasonic pretreatment is used when the composite bacterial material is mixed with water, and the power density of the ultrasonic pretreatment is 2-5 W / cm 2 , frequency is 20~30kHz, time is 5~15min.

[0023] Note: The above treatment can improve the fluidity of the composite bacterial slurry and make the composite bacterial material fully dispersed in the composite bacterial slurry, thereby improving its effect in the preparation of agricultural waste fermentation products, thereby obtaining agricultural waste fermentation products with good use effects.

[0024] Furthermore, in step 2, the cadmium contaminated soil is first plowed, and then covered with a film for 1-2 days, and then the Sedum serrata seedlings are transplanted into the cadmium contaminated soil.

[0025] Note: By covering the ground with film for 1-2 days, the fermented agricultural waste can adapt to the environment with the cadmium-contaminated soil, and the temperature of the cadmium-contaminated soil can be pre-elevated, so that the temperature of the cadmium-contaminated soil can more easily reach the planting temperature requirement of 8-25°C, avoiding the phenomenon of vernalization of Sedum serrata seedlings due to low temperature in the early stage of transplantation, and improving the survival rate.

[0026] The beneficial effects of the present invention are: The present invention can prevent the low-temperature vernalization of Sedum sedum from causing the death of most plants after flowering by anti-vernalization treatment and planting of Sedum sedum, thereby effectively extending its vegetative growth cycle and further improving the efficiency of absorbing and repairing cadmium in cadmium-contaminated soil; In addition, through the landfill and tillage of agricultural waste fermentation products, on the one hand, agricultural waste can be utilized as a resource, and on the other hand, the fertility of contaminated soil can be further improved and the growth of Sedum sedum can be promoted. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a data chart showing the effect of temperature on the chlorophyll a content in the leaves of Sedum sedum; Figure 2 This is a data chart showing the effect of temperature on the chlorophyll b content in the leaves of Sedum sedum; Figure 3 This is a data chart showing the effect of temperature on the total chlorophyll content in the leaves of Sedum sedum; Figure 4 This is a data chart showing the effect of temperature on the carotenoid content in the leaves of Sedum sedum; Figure 5 This is a data chart showing the effect of temperature on the content of malondialdehyde in the leaves of Sedum sedum; Figure 6 This is a data chart showing the effect of temperature on the content of soluble sugar in the leaves of Sedum sedum; Figure 7 This is a data chart showing the effect of temperature on the starch content in the leaves of Sedum sedum; Figure 8 This is a data chart showing the effect of temperature on the content of soluble protein in the leaves of Sedum serrata. Fig. 9 This is a data chart showing the effect of temperature on the total nitrogen content in the leaves of Sedum sedum; Fig.10 This is a data graph showing the effect of temperature on the carbon-nitrogen ratio in the leaves of Sedum serrata. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific implementation methods to better reflect the advantages of the present invention.

[0029] Embodiment 1: A method for remediating cadmium-contaminated soil, comprising the following steps: Step 1, performing anti-vernalization treatment on the branches of Sedum serrata to obtain Sedum serrata seedlings; wherein the anti-vernalization treatment is: raising the branches of Sedum serrata in a temperature environment of 23° C. for 35 days, and when the branches of the Sedum serrata seedlings have a diameter greater than 3 mm and a height greater than 10 cm, they can be used for transplantation; Step 2, then transplanting the Sedum sedum seedlings into cadmium-contaminated soil, during the planting and growth period of the Sedum sedum seedlings, controlling the ambient temperature at 23°C, when the ambient temperature is lower than 23°C, controlling the ambient temperature of the Sedum sedum seedlings at 23°C by building a greenhouse, and when the ambient temperature is higher than 23°C, controlling the growth ambient temperature of the Sedum sedum seedlings at 23°C by building a shade net, and regularly performing field management; Wherein, in step 2, the seedlings of Sedum serrata are transplanted at a planting density of 15 cm×15 cm. It should be noted that the field management includes irrigation, drainage, topdressing, insecticide and weeding. The insecticide adopts conventional agricultural control methods, the topdressing adopts commercially available organic fertilizers, and the weeding adopts a special herbicide for Sedum serrata and manual weeding. Step 3: When the branches of the Sedum serrata show no obvious growth within 15 to 20 days, its biomass has reached its maximum value, and the Sedum serrata is harvested and removed from the field.

[0030] Example 2: This example is different from Example 1 in that, in step 1, the branches of Sedum serrata are grown in an environment with a temperature of 8°C for 30 days.

[0031] Example 3: This example is different from Example 1 in that, in step 1, the branches of Sedum serrata are grown in a temperature environment of 25°C for 90 days.

[0032] Example 4: The difference between this example and Example 1 is that, in step 2, during the planting and growth period of the Sedum serrata seedlings, the ambient temperature is controlled at 8°C. When the ambient temperature is lower than 8°C, a greenhouse is built to control the ambient temperature of the Sedum serrata seedlings at 8°C. When the ambient temperature is higher than 8°C, a shade net is built to control the growth environment temperature of the Sedum serrata seedlings at 8°C.

[0033] Example 5: The difference between this example and Example 1 is that, in step 2, during the planting and growth period of the Sedum serrata seedlings, the ambient temperature is controlled at 30°C. When the ambient temperature is lower than 30°C, a greenhouse is built to control the ambient temperature of the Sedum serrata seedlings at 30°C. When the ambient temperature is higher than 30°C, a shade net is built to control the growth environment temperature of the Sedum serrata seedlings at 30°C.

[0034] In order to find out the critical temperature of vernalization of Sedum sedum, the following experiment is designed: 1) Test materials: The seedlings of Sedum serrata were collected from Zhehai Town, Huize County, Qujing City, Yunnan Province. The contaminated soil was collected from Guilin Town, She County, Anhui Province. The soil pH was 8.14, and the total amount of Cd and Zn was 6.21 mg kg -1 and 280 mg kg -1 ; 2) Experimental design and implementation: The pot experiment was conducted in the greenhouse of Nanjing Institute of Soil Science, Chinese Academy of Sciences. Square plastic pots with a length × width × height of 8 cm × 8 cm × 8 cm were selected, and each pot was filled with 500 g of soil. After two months of seedling cultivation, healthy seedlings of Sedum serrata with consistent growth were selected and placed in a constant temperature and light growth chamber for cultivation. Three groups of temperature treatments were set, including 4 ℃, 8 ℃ and 12 ℃, and the time of the three temperature treatments was set for 14, 21, 28, 35, 42, 49, and 56 days, respectively, for a total of 7 different cultivation time periods; in addition, three treatments were set, including outdoor normal temperature treatment in winter, constant temperature and light growth chamber treatment at 23 ℃ (control), and 4 ℃ cultivation until April 23, 2024 (123 days) and then moved to normal temperature environment; a total of 24 experimental treatments, each treatment was repeated 3 times, and each treatment included 8 Sedum serrata plants. The experiments of different treatments all started on December 22, 2023. After the cultivation time of 7 different time periods in the low temperature treatment group was over, the potted plants were transferred to a constant temperature and light growth box at 23 °C for further cultivation. After the flower buds appeared, the flowering of Sedum serrata was observed every day, the number of flowers was counted, and the flowering rate was calculated. 0.05 g urea and 0.05 g potassium dihydrogen phosphate were applied as basal fertilizer to each pot, and 0.025 g urea and potassium dihydrogen phosphate were applied to each pot on March 5, 2024. Water every day to ensure the water required for the growth of Sedum serrata; 3) Sample collection and processing: Since there was no vernalization in the 8 ℃ and 12 ℃ treatment groups, four treatments were selected, including the winter outdoor normal temperature treatment, the 23 ℃ treatment (CK), the 4 ℃ treatment for 123 days, and the 4 ℃ treatment for 56 days. Sampling was carried out on April 23, 2024 and June 20, 2024. The two time points were the 16 days before flowering and the flowering period of the 4 ℃ treatment for 56 days, and the early flowering and flowering period of the winter outdoor normal temperature treatment and the 4 ℃ treatment for 123 days. Although the 23 ℃ treatment (CK) did not bloom, plant samples were also taken at the same time. 1~2 true leaves and part of the stem tip near the apex of the apex were collected. Some fresh samples were chopped and mixed for the determination of physiological and biochemical indicators; the other fresh samples were washed with deionized water, wiped dry, and dried at 105 ℃ for 20 min, then dried at 70 ℃ to constant weight, and crushed for use. The last batch of samples was harvested on July 2, 2024. The upper part of the companion ore sceneries was collected, washed with tap water and deionized water, fixed, dried, and weighed; 4) Determination method: Flowering index: The calculation formula for the flowering rate of each treatment is: flowering rate (%) = number of flowering plants / total number of plants × 100; first flowering date: the date when the first flowering plant appears in the group; Physiological and biochemical indicators: refer to the methods in "Principles and Techniques of Plant Physiological and Biochemical Experiments" for determination. The 95% ethanol grinding extraction method is used to determine the content of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids. The thiobarbituric acid (TBA) method is used to determine the content of malondialdehyde. The soluble sugar and starch content is determined by anthrone colorimetry. The soluble protein content is determined by Coomassie Brilliant Blue G-250 method. The total N content is determined by Kjeldahl nitrogen determination. The content of chlorophyll, soluble sugar, malondialdehyde, soluble sugar and starch is the content of fresh weight, and the total N content is the content of dry weight. C / N = total sugar / total nitrogen (total sugar = soluble sugar + starch); Growth index determination: At the time of the test harvest, the plant height of Sedum truncatum was measured with a steel ruler with an accuracy of 0.1 mm, the stem diameter of Sedum truncatum was measured with a 1 / 1000 vernier caliper, and the dry weight of the Sedum truncatum sample was weighed with a 1 / 1000 electronic balance; Data processing and analysis: Excel 2010 and SPSS 19.0 software were used to perform correlation analysis on the data, the least significant difference method (LSD) was used for significant difference test (p < 0.05), and Origin 2021 software was used for drawing; 5) Results and analysis Effects of different temperatures and durations on the flowering of Sedum sedum: As shown in Table 1, the 8 °C, 12 °C and 23 °C (CK) treatment groups did not show flowering after different periods of cultivation, while the 4 °C treatment group showed flowering after 35-56 days. The 4 °C treatment group was moved into a 23 °C growth chamber after 56 days of treatment. The first flowering plant of the 4 °C treatment group was observed on May 9, 2024 (83rd day), and the flowering rate reached more than 90.0% after 94 days. The first flowering date of the 4 °C treatment group treated with normal outdoor temperature in winter was June 14, 2024, which was 36 days later than the 4 °C treatment group for 56 days. In addition, with the extension of the 4 °C low temperature treatment time (35-56 days), the first flowering date of the 4 °C treatment group was advanced and the flowering rate increased. The flowering rate reached 100% at 49 days and 56 days of low temperature treatment. Therefore, the critical temperature for vernalization of Sedum serrata is between 4-8 °C. Vernalization occurs after 35 days of treatment at 4 °C, and it is fully vernalized after 49 days.

[0035] Table 1 Effects of different temperature and duration treatments on the flowering rate and first flowering date of Sedum serrata ; The values ​​in Table 1 are mean ± standard deviation.

[0036] The results of the effects of different temperature and duration treatments on the aboveground growth of the mineral-bearing sedum: Table 2 lists the changes in stem diameter, plant height and aboveground biomass of Sedum serrata at the flowering stage under different temperature and duration treatments. After 14, 21 or 28 days of 4 °C treatment, there was no significant difference in stem diameter and plant height between Sedum serrata and the 8 °C and 12 °C temperature treatments with the same culture time; however, after 35, 42, 49 or 56 days of 4 °C treatment, the stem diameter and plant height of Sedum serrata were significantly higher than those of the 8 °C and 12 °C treatments with the same culture time, and also significantly higher than those of the 23 °C treatment group (CK). After being treated at 4 °C, 8 °C and 12 °C for a certain period of time and then placed at 23 °C, the plants grew normally and the survival rate reached 100%. Under the same treatment time conditions (35-56 d), there was no significant difference in the aboveground biomass of Sedum sedum treated at 4 °C and 8 °C, 12 °C and 23 °C (CK) temperature treatments, but the aboveground biomass of Sedum sedum treated at normal outdoor temperature in winter was significantly lower than that of other temperature treatments. With the extension of low temperature treatment time, the stem diameter and plant height of Sedum sedum treated at 4 °C showed a significant growth trend, but the difference in aboveground biomass of Sedum sedum did not reach a significant level.

[0037] Table 2 Effects of different temperature and duration treatments on the growth of Sedum serrata during its flowering period ; In Table 2, different capital letters in the same column indicate significant differences (p < 0.05), and different lowercase letters in the same row indicate significant differences (p < 0.05).

[0038] Effects of different temperatures and their duration on the chlorophyll content of Sedum sedum leaves: Figure 1-Figure 4The changes of chlorophyll and carotenoid contents in leaves of Sedum serrata under different temperature treatments before and during flowering were given. Compared with before flowering, the chlorophyll a, chlorophyll b and total chlorophyll contents of plants treated with normal outdoor temperature, 4 °C for 56 d and 4 °C for 123 d decreased significantly during flowering, while the chlorophyll content of Sedum serrata plants treated with 23 °C (CK) did not change significantly during flowering. Compared with the 23 °C treatment (CK), the 4 °C treatment for 56 days had no significant effect on the chlorophyll a, chlorophyll b and total chlorophyll contents of Sedum serrata before flowering, but significantly reduced the chlorophyll a, chlorophyll b and total chlorophyll contents by 50.3%, 41.8% and 47.4% at the flowering stage; however, the chlorophyll a, chlorophyll b and total chlorophyll contents of Sedum serrata treated at 4 °C for 123 days all decreased significantly, with a significant decrease of 25.1%, 24.5% and 24.9% before flowering, and a significant decrease of 69.1%, 51.1% and 62.8% at the flowering stage. Compared with the 23 °C treatment (CK), the carotenoid contents at the flowering stage of 4 °C treatments for 56 and 123 days increased significantly by 25.9% and 32.2%. Therefore, the 4 °C treatment significantly reduced the chlorophyll content, which was more significant during the flowering period; when the 4 °C treatment was increased from 56 d to 123 d, the chlorophyll content before flowering also decreased significantly.

[0039] Effects of different temperatures and their duration on the content of malondialdehyde in the leaves of Sedum serrata: Depend on Figure 5 It can be seen that under different temperature treatment conditions, there was no significant difference in the malondialdehyde (MDA) content of the leaves of Sedum serrata before flowering and in full flowering. Compared with the 23 °C treatment group (CK), the MDA content of the leaves of Sedum serrata treated at 4 °C for 56 days, 4 °C for 123 days and outdoor normal temperature treatment increased significantly by 22.4%, 41.9% and 71.2% before flowering, and increased significantly by 25.6%, 40.2% and 52.6% during full flowering (p<0.05).

[0040] Effects of different temperatures and their duration on carbon and nitrogen metabolism in leaves of Sedum sedum: from Figure 6-Figure 10It can be seen that the soluble sugar and starch content of the leaves of Sedum serrata in the 23 °C treatment group (CK) was significantly higher in the early flowering stage than in the full flowering stage, while the soluble sugar and starch content of the leaves in the treatment group treated with normal outdoor temperature and 4 °C for 56 days was significantly higher in the full flowering stage than in the early flowering stage. Compared with before flowering, the soluble protein content of the leaves of Sedum serrata in the full flowering stage increased significantly under different temperature treatments, while the total nitrogen content of the leaves decreased significantly. By calculating the total sugar / total nitrogen (C / N), it can be found that the C / N ratio of the leaves of the three low temperature treatment groups of the final outdoor normal temperature, 4 °C treatment for 56 days and 4 °C treatment for 123 days was significantly higher in the full flowering stage than before flowering, while the C / N ratio of the leaves of the 23 °C treatment group decreased significantly with the increase of growth time.

[0041] Compared with the 23 °C treatment group (CK), there were no significant differences in the soluble sugar, starch, soluble protein and total nitrogen contents of the leaves of Sedum serrata treated at 4 °C for 56 days in the early flowering stage, but the soluble sugar, starch and soluble protein contents of the leaves increased significantly, while the total nitrogen content decreased significantly in the full flowering stage. In the full flowering stage, the soluble sugar, starch and soluble protein contents of the leaves of the treatment groups treated at room temperature outdoors and 4 °C for 123 days were also significantly higher than those of the 23 °C treatment group (CK), while the total nitrogen content of the leaves was significantly lower than that of the 23 °C treatment group (CK). Further analysis showed that the C / N ratio of the leaves of Sedum serrata in the three low temperature treatment groups of room temperature outdoors, 4 °C for 56 days and 4 °C for 123 days was also significantly higher than that of the 23 °C treatment group in the full flowering stage. Therefore, compared with non-vernalized plants, low temperature-induced vernalization will significantly increase the soluble sugar, starch and soluble protein contents of the leaves of Sedum serrata during the flowering period, but will reduce the total nitrogen content of the leaves, thereby increasing the C / N ratio.

[0042] Effect of Sedum sedum on soil cadmium removal: Table 3 lists the effects of Sedum sutchuenensis on soil Cd removal after 56 days of different temperature treatments. After 56 days of 4 °C treatment, the Cd removal of Sedum sutchuenensis was significantly lower than that of other temperature treatments; while there was no significant difference between the temperature treatments of 23 °C (CK), 12 °C, 8 °C and room temperature groups, but the room temperature group had higher temperature requirements for thermal insulation control than the CK group. Therefore, the comprehensive effect of the Sedum sutchuenensis treatment in the CK group was better.

[0043] Table 3 Effects of Sedum robur on Cd removal in soil after 56 days of treatment with different temperatures ;

[0044] Example 6: This example is different from Example 1 in that, in step 2, the Sedum serrata seedlings are transplanted at a planting density of 12 cm×12 cm.

[0045] Example 7: This example is different from Example 1 in that, in step 2, the Sedum serrata seedlings are transplanted at a planting density of 25 cm×25 cm.

[0046] In order to verify the effect of the above treatment on the removal of soil cadmium by Sedum sedum, a rectangular plot of 10m×6m in length×width was set to simulate the planting density, and the above test method was used to test the removal amount of Cd in each embodiment. The results are shown in Table 4 below: Table 4 Effects of different remediation methods on the removal of Cd in soil after 56 days of treatment with Sedum sedum ; Table 4 lists the effects of Sedum sutchuenensis on the removal of Cd in the soil under different treatment processes. The amount of Cd removed showed a significant change after changing the planting density of Sedum sutchuenensis seedlings. In Example 6, the amount of Cd removed decreased after the planting density was reduced. This may be due to insufficient Cd absorption caused by the sparse planting density, resulting in a decrease in Cd removal. In Example 7, the amount of Cd removed also decreased after the planting density was increased. This may be due to excessive competition between plants caused by the dense planting density, thereby affecting the enrichment of Cd in the soil by Sedum sutchuenensis.

[0047] Example 8: This example is different from Example 1 in that, in step 2, before the Sedum sedum seedlings are planted in the cadmium-contaminated soil, the cadmium-contaminated soil is plowed and fertilized, and the plowing and fertilizing method is: The fermented agricultural waste was applied to the cadmium-contaminated soil at a rate of 1300 kg / mu, followed by plowing. After the cadmium-contaminated soil was plowed, the cadmium-contaminated soil was covered with a film for 1.5 days, and then the Sedum serrata seedlings were transplanted into the cadmium-contaminated soil. Since it is in the south, the fermented agricultural waste described in this embodiment is obtained by fermenting agricultural waste, and the agricultural waste is crops grown in local non-polluted areas, selected from rice straw.

[0048] Wherein, the preparation method of the agricultural waste fermentation product is: 1) Build a fermentation frame with a height of 5m, a width of 2.5m and a length of 2.5m. Cut the agricultural waste into pieces of 4cm and spread them in layers in the fermentation frame. The thickness of each layer of agricultural waste is 25cm. 2) After each layer of agricultural waste is filled, water at 13°C is sprayed on each layer of agricultural waste to keep the moisture content of the agricultural waste at 45%, and then the composite bacterial slurry is evenly sprayed. The spraying thickness of the composite bacterial slurry is 4 cm. 3) After the agricultural waste is layered and filled, fermentation is performed for 4 days to obtain the fermented agricultural waste; The composite bacterial slurry is obtained by mixing the composite bacterial material and water in a mass ratio of 25:7, and ultrasonic pretreatment is used when the composite bacterial material and water are mixed. The power density of the ultrasonic pretreatment is 4W / cm 2 , frequency is 25kHz, time is 12min; in terms of mass fraction, the composite bacterial feed consists of 47 parts of Bacillus polymyxa, 8 parts of Bacillus subtilis, 5 parts of Enterococcus faecalis, 240 parts of straw powder, 70 parts of urea and 32 parts of superphosphate; wherein the straw powder is a powder obtained by ball-milling rice straw or corn straw through an 80-mesh sieve.

[0049] Example 9: This example is different from Example 8 in that 800 kg / mu of fermented agricultural waste is applied to the cadmium-contaminated soil, which is then plowed and covered with a film for 1 day.

[0050] Example 10: This example is different from Example 8 in that the fermented agricultural waste is applied to the cadmium-contaminated soil at a rate of 1500 kg / mu, followed by plowing. After the cadmium-contaminated soil is plowed, the cadmium-contaminated soil is covered with a film for 2 days.

[0051] Example 11: This example is different from Example 8 in that a fermentation frame with a height of 4m, a width of 2m and a length of 2m is constructed, and the agricultural waste is chopped into 3cm and spread in layers in the fermentation frame, and the thickness of each layer of agricultural waste is 20cm.

[0052] Example 12: This example is different from Example 8 in that a fermentation frame with a height of 6 m, a width of 3 m and a length of 3 m is constructed, and the agricultural waste is chopped into 5 cm pieces and spread in layers in the fermentation frame, and the thickness of each layer of agricultural waste is 30 cm.

[0053] Example 13: This example is different from Example 8 in that 10°C water is sprayed on each layer of agricultural waste to keep the moisture content of the agricultural waste at 40%, and then the composite bacterial slurry is evenly sprayed with a spray thickness of 2 cm. After the agricultural waste is layered and filled, it is fermented for 3 days.

[0054] Example 14: This example is different from Example 8 in that 15°C water is sprayed on each layer of agricultural waste to keep the moisture content of the agricultural waste at 50%, and then the composite bacterial slurry is evenly sprayed with a spray thickness of 5 cm. After the agricultural waste is layered and filled, it is fermented for 5 days.

[0055] Example 15: This example is different from Example 8 in that the composite bacterial slurry is obtained by mixing the composite bacterial material and water in a mass ratio of 20:7, and ultrasonic pretreatment is used when the composite bacterial material and water are mixed. The power density of the ultrasonic pretreatment is 2W / cm 2, frequency is 20kHz, time is 5min.

[0056] Example 16: This example is different from Example 8 in that the composite bacterial slurry is obtained by mixing the composite bacterial material and water in a mass ratio of 30:7, and ultrasonic pretreatment is used when the composite bacterial material and water are mixed. The power density of the ultrasonic pretreatment is 5W / cm 2 , frequency is 30kHz, time is 15min.

[0057] Example 17: This example is different from Example 8 in that, measured by mass, the composite bacterial material consists of 40 parts of Bacillus polymyxa, 5 parts of Bacillus subtilis, 2 parts of Enterococcus faecalis, 150 parts of straw powder, 50 parts of urea and 10 parts of superphosphate; wherein the straw powder is a powder obtained by ball-grinding rice straw through a 50-mesh sieve.

[0058] Example 18: This example is different from Example 8 in that, measured by mass, the composite bacterial material consists of 50 parts of Bacillus polymyxa, 10 parts of Bacillus subtilis, 7 parts of Enterococcus faecalis, 300 parts of straw powder, 80 parts of urea and 40 parts of superphosphate; wherein the straw powder is a powder obtained by ball-grinding rice straw through a 100-mesh sieve.

[0059] In order to verify the effect of the above treatment on the removal of soil cadmium by Sedum sedum, the above test method was used to test the removal amount of Cd in each embodiment, and the results are shown in Table 5 below: Table 5 Effects of different remediation methods on the removal of Cd in soil after 56 days of treatment with Sedum sedum ; Table 5 lists the amount of Cd removed from soil by Sedum oxyphylla under different treatment processes. After landfilling and tilling with fermented agricultural waste, the amount of Cd removed by Sedum oxyphylla from Cd-contaminated soil was improved to a certain extent; In Example 9, after the landfill amount of agricultural waste fermentation products and the film covering time were changed, the Cd removal amount decreased. This may be because the landfill amount of agricultural waste fermentation products was too small and the ideal use effect was not achieved. In Example 10, after the landfill amount of agricultural waste fermentation products and the film covering time were changed, the Cd removal amount did not change significantly. This may be because the landfill amount of agricultural waste fermentation products has been saturated. In Example 11 and Example 12, after changing the filling specifications and thickness of agricultural waste, the Cd removal amount decreased. This may be because the different single-layer agricultural waste filling thickness affects the preparation effect of agricultural waste fermentation, thereby affecting the use performance of agricultural waste fermentation. In Example 13 and Example 14, the amount of Cd removal decreased after the addition amount of the composite bacterial slurry and the moisture content were changed. This may be because the different temperatures of the sprinkling water and the amount of the composite bacterial slurry used affected the preparation effect of the agricultural waste fermentation product. When the amount of the composite bacterial slurry added was too large, it was easy for the agricultural waste fermentation product to release a large amount of heat in advance during the fermentation process, thereby affecting the subsequent use effect of landfilling in cadmium-contaminated soil. When the amount of the composite bacterial slurry added was too small, the use performance of the agricultural waste fermentation product was reduced. In Example 15, after the preparation conditions of the composite bacterial material were changed, the amount of Cd removal decreased. This may be due to the small amount of composite bacterial material in the composite bacterial slurry and insufficient mixing, which did not achieve the ideal use effect. In Example 16, after the preparation conditions of the composite bacterial material were changed, the amount of Cd removal did not change significantly. This may be due to the fact that the amount of composite bacterial material in the composite bacterial slurry and the mixing have tended to saturation. In Example 17 and Example 18, the Cd removal amount decreased after the composition of the composite bacterial material was changed. This may be because the different composition of the composite bacterial material affected the use effect of the composite bacterial slurry, thereby affecting the use performance of the agricultural waste fermentation product.

Claims

1. A method for remediating cadmium-contaminated soil, characterized in that: The following steps are involved: Step 1, performing anti-vernalization treatment on the branches of Sedum serrata to obtain Sedum serrata seedlings; wherein the anti-vernalization treatment is: raising the branches of Sedum serrata in a temperature environment of 8-25°C for 30-90 days; Step 2: subsequently transplanting the Sedum sedum seedlings into cadmium-contaminated soil, controlling the ambient temperature at 8-30° C. during the planting and growth of the Sedum sedum seedlings, and performing field management regularly; Step 3: When the branches of the Sedum serrata show no obvious growth within 15 to 20 days, harvest the Sedum serrata and remove the harvest from the field.

2. The method for remediating cadmium-contaminated soil according to claim 1, characterized in that: In step 2, the Sedum serrata seedlings are transplanted at a planting density of 12~25cm×12~25cm.

3. The method for remediating cadmium-contaminated soil according to claim 1, characterized in that: In step 2, the field management includes irrigation, drainage, topdressing, insecticide and weeding.

4. The method for remediating cadmium-contaminated soil according to claim 1, characterized in that: In step 2, when the ambient temperature is lower than 8°C, the ambient temperature of the Sedum serrata seedlings is controlled at 8-30°C by covering with film, greenhouse or configuring heating equipment; when the ambient temperature is higher than 30°C, the ambient temperature of the Sedum serrata seedlings is controlled at 8-30°C by building a shade net or configuring cooling equipment.

5. The method for remediating cadmium-contaminated soil according to claim 1, characterized in that: In step 2, before the Sedum sedum seedlings are transplanted into the cadmium-contaminated soil, the cadmium-contaminated soil is tilled and fertilized, and the tillage and fertilization method is as follows: Fermented agricultural waste was applied to cadmium-contaminated soil at a rate of 800-1500 kg / mu, followed by tillage.

6. The method for remediating cadmium-contaminated soil according to claim 5, characterized in that: The agricultural waste fermentation product is obtained by fermenting agricultural waste, and the agricultural waste is crops grown in local non-polluted areas, selected from rice straw or corn straw.

7. The method for remediating cadmium-contaminated soil according to claim 6, characterized in that: The fermentation method of the agricultural waste fermentation product is: 1) Build a fermentation frame with a height of 4-6m, a width of 2-3m, and a length of 2-3m. Cut the agricultural waste into pieces of 3-5cm and spread them in layers in the fermentation frame. The thickness of each layer of agricultural waste is 20-30cm. 2) After each layer of agricultural waste is filled, water at 10-15°C is sprayed on each layer of agricultural waste to keep the moisture content of the agricultural waste at 40-50%, and then the composite bacterial slurry is evenly sprayed. The spraying thickness of the composite bacterial slurry is 2-5 cm. 3) After the agricultural waste is layered and filled, it is fermented for 3-5 days to obtain the fermented agricultural waste.

8. The method for remediating cadmium-contaminated soil according to claim 7, characterized in that: The composite bacterial slurry is obtained by mixing composite bacterial material and water in a mass ratio of 20-30:7; The composite bacterial feed is composed of 40-50 parts of Bacillus polymyxa, 5-10 parts of Bacillus subtilis, 2-7 parts of Enterococcus faecalis, 150-300 parts of straw powder, 50-80 parts of urea and 10-40 parts of superphosphate by weight; The straw powder is a powder obtained by ball-grinding rice straw or corn straw through a 50-100 mesh sieve.

9. The method for remediating cadmium-contaminated soil according to claim 8, characterized in that: Ultrasonic pretreatment is used when the composite bacterial material is mixed with water. The power density of the ultrasonic pretreatment is 2-5 W / cm 2 , frequency is 20~30kHz, time is 5~15min.

10. The method for remediating cadmium-contaminated soil according to claim 7, characterized in that: In step 2, the cadmium-contaminated soil is first plowed, and then covered with a film for 1-2 days, and then the Sedum serrata seedlings are transplanted into the cadmium-contaminated soil.

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