A method for remediating cadmium-polluted soil

Abstract

The present invention discloses a method for repairing cadmium-polluted soil. By subjecting Sedum plumbizincicola branches to seedling anti-vernalization treatment, Sedum plumbizincicola seedlings are obtained. Subsequently, the Sedum plumbizincicola seedlings are transplanted into cadmium-polluted soil. During the planting and growth period of the Sedum plumbizincicola seedlings, the environmental temperature is controlled at 8-25 °C, and field management is carried out regularly. When there is no obvious growth of the Sedum plumbizincicola branches within 15-20 days, the Sedum plumbizincicola is harvested and the harvested product is removed from the field. Through the anti-vernalization treatment and planting of Sedum plumbizincicola, the present invention can avoid the phenomenon that most plants die after flowering due to low-temperature vernalization of Sedum plumbizincicola, thereby effectively extending its vegetative growth period, and further improving the absorption and repair efficiency of cadmium in cadmium-polluted soil.

Description

Technical Field

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

[0002] Sedum plumbizincicola ( Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu) is a new species of the genus Sedum in the family Crassulaceae, which has the characteristics of being perennial, having a large biomass, and being easy to harvest. It is a hyperaccumulator of heavy metals cadmium (Cd) and zinc (Zn), and can effectively remove Cd and Zn in polluted soil. The enrichment coefficient of Sedum plumbizincicola for Cd (the ratio of the concentration in the above-ground part of the plant to the soil concentration) can reach more than 100, and it is an important plant resource for the repair of Cd-polluted farmland soil. Over the past decade or so, Sedum plumbizincicola has achieved good practical results in the repair of Cd-polluted farmland soil, and has broad application prospects. However, during the process of popularization and application, after experiencing winter low-temperature vernalization and flowering and seed setting in summer, most of the branches of Sedum plumbizincicola will wither, and the remaining part will grow slowly. This phenomenon has an important impact on its subsequent large-scale planting and the efficient absorption and repair of soil heavy metals, and is an urgent problem to be solved.

[0003] Vernalization refers to the process in which winter plants sense the environmental low temperature, turn from vegetative growth to reproductive growth, and finally induce the plants to flower. Vernalization can cause non-flowering plants to flower or flower earlier, which is of great significance to agricultural production. Vernalization technology has been applied to various vegetables, flowers and medicinal materials, such as Brassica rapa var. rosularis ( Brassica narinosa ), broad bean ( Vicia faba ), lily ( Lilium brownii ), angelica ( Angelica sinensis ), etc., and good results have been achieved. However, due to the different growth environments and states of different species, the requirements for vernalization conditions also vary. Therefore, studying the vernalization conditions required by the Cd hyperaccumulator Sedum plumbizincicola and its response to low temperature in the growth environment will help Sedum plumbizincicola avoid vernalization, promote vegetative growth, and improve its phytoremediation efficiency for Cd in polluted soil.

[0004] Low-temperature vernalization can cause changes in physiological indexes such as nucleic acid metabolism, endogenous hormone metabolism and carbon-nitrogen metabolism in plants. The carbon-nitrogen ratio (C / N) is considered to be the main determinant in the process of plant flowering. Among them, carbohydrates not only provide energy for the physiological metabolism process of flowering, but also directly participate in the physiological reactions of flowering. A higher soluble sugar content is helpful for the development of the flower stem and makes it easier to bolt; proteins play an important role in the life activities of cells and are an important material basis for flowering. By measuring the changes in the contents of soluble sugar, starch, soluble protein and total nitrogen, the change of the C / N ratio can be deduced; the higher the C / N ratio, the greater the possibility of plant bolting and flowering.

[0005] Although a number of studies have revealed the importance of plant vernalization, there has been no systematic study on the low-temperature vernalization of Sedum plumbizincicola, a cadmium-zinc hyperaccumulating plant, and the critical temperature and duration of vernalization are not yet clear. Therefore, there is a need for a method to improve the remediation effect of cadmium-contaminated soil by anti-vernalization treatment of Sedum plumbizincicola to solve the above problems. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for remediating cadmium-contaminated soil.

[0007] The technical solution of the present invention is: a method for remediating cadmium-contaminated soil, comprising the following steps:

[0008] Step 1: Perform anti-vernalization treatment on Sedum plumbizincicola branches to obtain Sedum plumbizincicola seedlings; wherein, the anti-vernalization treatment is: raise Sedum plumbizincicola branches in a temperature environment of 8-25°C for 30-90 days;

[0009] Step 2: Subsequently transplant the Sedum plumbizincicola seedlings into cadmium-contaminated soil. During the growth period of the Sedum plumbizincicola seedlings, control the environmental temperature at 8-30°C and perform regular field management;

[0010] Step 3: When there is no obvious growth of the Sedum plumbizincicola branches within 15-20 days, harvest the Sedum plumbizincicola and remove the harvested product from the field.

[0011] Further, in Step 2, the Sedum plumbizincicola seedlings are transplanted at a planting density of 12-25 cm × 12-25 cm.

[0012] Note: Appropriate planting density can ensure sufficient space and light between Sedum plumbizincicola plants, promote photosynthesis and gas exchange, and is beneficial to the healthy growth of plants. At the same time, appropriately increasing the planting density can shorten its growth cycle. Good ventilation conditions also help reduce the occurrence of pests and diseases. Reasonable planting density can avoid excessive competition between plants, ensure that each Sedum plumbizincicola plant can obtain sufficient nutrients and water to meet its growth and development needs. And appropriate planting density can promote the growth of the above-ground part of Sedum plumbizincicola, 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 of Sedum plumbizincicola and the heavy metal uptake can be optimized, thereby shortening the remediation time limit of contaminated soil and controlling the remediation cost. Moreover, appropriate planting density can also ensure uniform uptake of heavy metals in the soil by Sedum plumbizincicola, avoid local over-uptake or insufficient uptake, and improve the remediation quality and efficiency.

[0013] Further, in Step 2, the field management is irrigation, drainage, topdressing, pest control, and weeding.

[0014] Explanation: Irrigation and drainage are appropriately adjusted according to crop requirements and soil conditions, which can provide suitable moisture conditions for crops; weeding can prevent weeds from competing with crops for nutrients, moisture, 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.

[0015] Biological control, chemical control, or agricultural control, etc. are adopted to reduce the damage of pests and diseases to crops, and pests and diseases problems are discovered and handled in a timely manner to prevent their spread and proliferation; through the conventional field management of Sedum plumbizincicola, the growth and cadmium accumulation and enrichment effect of Sedum plumbizincicola can be improved, the growth environment of Sedum plumbizincicola can be optimized, and the growth of Sedum plumbizincicola can be promoted.

[0016] Furthermore, in step 2, when the environmental temperature is lower than 8°C, the environmental temperature of Sedum plumbizincicola seedlings is controlled at 8 - 30°C by means of film mulching, greenhouse, or configuring warming equipment; when the environmental temperature is higher than 30°C, the environmental temperature of Sedum plumbizincicola seedlings is controlled at 8 - 30°C by means of building a shade net or configuring cooling equipment.

[0017] Explanation: Through film mulching, greenhouse, or warming equipment, the soil or air temperature can be increased, enabling it to effectively absorb and preserve solar radiant energy and convert it into heat energy to transfer or affect the soil, thereby increasing the soil environmental temperature. At the same time, this is also a commonly used method for controlling environmental temperature in current plant cultivation, which has good economy and mature technology; building a shade net can effectively prevent the transmission of solar radiant energy to the ground surface, and configuring cooling equipment is also a commonly used method for effectively reducing the environmental temperature, and it is also a means of reducing the ground surface temperature under high-temperature climate conditions with good economy and mature technology.

[0018] Furthermore, in step 2, before transplanting Sedum plumbizincicola seedlings into cadmium-contaminated soil, the cadmium-contaminated soil is plowed and fertilized, and the plowing and fertilization method is as follows:

[0019] The fermented product of agricultural waste is applied to the cadmium-contaminated soil at 800 - 1500 kg / mu, and then plowing is carried out.

[0020] Explanation: Through the landfill and plowing of the fermented product of agricultural waste, on the one hand, the agricultural waste can be resourcefully utilized, and on the other hand, the soil can be fertilized and improved to promote the growth of Sedum plumbizincicola seedlings.

[0021] Even further, the fermented product of agricultural waste is obtained by fermenting agricultural waste, and the agricultural waste is crops planted in local non-polluted areas, selected from rice straw or corn straw.

[0022] Note: Corn straw is often used as agricultural waste after planting northern crops, while rice straw is often used as agricultural waste after planting southern crops, which can be selected according to local production conditions. By reusing these agricultural wastes, on the one hand, it can avoid problems in agricultural waste treatment, and on the other hand, it can utilize resources to prepare a nutrient matrix that promotes Sedum plumbizincicola.

[0023] Furthermore, the fermentation method of the agricultural waste ferment is as follows:

[0024] 1) Construct 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 lay it in layers in the fermentation frame. The laying thickness of each layer of agricultural waste is 20 - 30cm.

[0025] 2) After laying each layer of agricultural waste, spray water at 10 - 15°C on each layer of agricultural waste to keep the moisture content of the agricultural waste at 40 - 50%. Then evenly spray the composite bacterial slurry, and the spraying thickness of the composite bacterial slurry is 2 - 5cm.

[0026] 3) After laying the agricultural waste in layers, ferment for 3 - 5 days to obtain the agricultural waste ferment.

[0027] Note: The above fermentation method can obtain an agricultural waste ferment with stable performance, so that in the subsequent landfill ploughing of the agricultural waste ferment, the soil temperature can be effectively controlled to reach the anti-vernalization temperature range of Sedum plumbizincicola, thus preventing the occurrence of vernalization in Sedum plumbizincicola.

[0028] By spraying water below room temperature on the 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 bacterium in the composite bacterial slurry, the agricultural waste ferment can play a better role in subsequent landfill ploughing, thereby controlling the soil temperature and maintaining soil fertility.

[0029] Furthermore, the composite bacterial slurry is obtained by mixing the composite bacterial material and water in a mass ratio of 20 - 30:7.

[0030] By mass, the composite bacterial material 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.

[0031] Among them, the straw powder is a powder obtained by ball-milling rice straw or corn straw through a 50 - 100 mesh sieve.

[0032] Description: The compound bacterial agent with the above ratio can effectively improve the use effect of agricultural waste fermented products. Paenibacillus polymyxa has broad-spectrum antagonistic activity, can effectively prevent the occurrence of various plant fungal, bacterial and nematode diseases, and can also produce substances such as plant hormones, promote plant growth and development, improve crop yield, and can produce a variety of enzymes such as cellulase; Bacillus subtilis can secrete a variety of active substances, such as subtilin, nystatin, bacitracin, etc., and these substances have broad-spectrum antibacterial effects; while 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 improve 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, and release more nutrients for plants to absorb and utilize.

[0033] Furthermore, when the compound bacterial agent is mixed with water, ultrasonic pretreatment is used, and the power density of the ultrasonic pretreatment is 2-5 W / cm 2 , the frequency is 20-30 kHz, and the time is 5-15 min.

[0034] Description: Through the above treatment, the fluidity of the compound bacterial slurry can be improved, and the compound bacterial agent can be fully dispersed in the compound bacterial slurry, thereby improving its effect in the preparation of agricultural waste fermented products, and obtaining agricultural waste fermented products with good use effects.

[0035] Furthermore, in step 2, after the cadmium-polluted soil is plowed, the cadmium-polluted soil is covered with a film for 1-2 days, and then the Sedum plumbizincicola seedlings are transplanted into the cadmium-polluted soil.

[0036] Description: By covering the film for 1-2 days, the agricultural waste fermented product can adapt to the cadmium-polluted soil environment, and at the same time, the temperature of the cadmium-polluted soil can be preheated, so that the temperature of the cadmium-polluted soil can more easily reach the planting temperature requirement of 8-25 °C, avoiding the phenomenon of vernalization due to too low temperature at the initial stage of transplanting of Sedum plumbizincicola seedlings, and improving the survival rate.

[0037] The beneficial effects of the present invention are:

[0038] Through the anti-vernalization treatment and planting of Sedum plumbizincicola, the present invention can avoid the phenomenon that most plants die after flowering due to low-temperature vernalization of Sedum plumbizincicola, thereby effectively extending its vegetative growth period, and then improving the absorption and repair efficiency of cadmium in cadmium-polluted soil;

[0039] And through the landfill and plowing of agricultural waste fermented products, on the one hand, the agricultural waste can be recycled, and on the other hand, the fertility of polluted soil can be further improved to promote the growth of Sedum plumbizincicola. Description of the Drawings

[0040] Figure 1 It is a data graph showing the influence of temperature on the content of chlorophyll a in the leaves of Sedum plumbizincicola;

[0041] Figure 2 It is a data graph showing the influence of temperature on the content of chlorophyll b in the leaves of Sedum plumbizincicola;

[0042] Figure 3 It is a data graph showing the influence of temperature on the total chlorophyll content in the leaves of Sedum plumbizincicola;

[0043] Figure 4 It is a data graph showing the influence of temperature on the carotenoid content in the leaves of Sedum plumbizincicola;

[0044] Figure 5 It is a data graph showing the influence of temperature on the malondialdehyde content in the leaves of Sedum plumbizincicola;

[0045] Figure 6 It is a data graph showing the influence of temperature on the content of soluble sugar in the leaves of Sedum plumbizincicola;

[0046] Figure 7 It is a data graph showing the influence of temperature on the starch content in the leaves of Sedum plumbizincicola;

[0047] Figure 8 It is a data graph showing the influence of temperature on the soluble protein content in the leaves of Sedum plumbizincicola;

[0048] Figure 9 It is a data graph showing the influence of temperature on the total nitrogen content in the leaves of Sedum plumbizincicola;

[0049] Figure 10 It is a data graph showing the influence of temperature on the carbon-nitrogen ratio in the leaves of Sedum plumbizincicola. Specific implementation manner

[0050] The present invention will be further described in detail below in combination with specific implementation manners to better reflect the advantages of the present invention.

[0051] Example 1: A method for remediating cadmium-polluted soil, comprising the following steps:

[0052] Step 1: Perform vernalization prevention treatment on Sedum plumbizincicola branches to obtain Sedum plumbizincicola seedlings; wherein, the vernalization prevention treatment is: raise Sedum plumbizincicola branches in a temperature environment of 23°C for 35 days, and when the diameter of the Sedum plumbizincicola seedling branches is greater than 3 mm and the height is greater than 10 cm, they can be used for transplantation;

[0053] Step 2: Subsequently, transplant the Sedum plumbizincicola seedlings into cadmium-contaminated soil. During the growth period of the Sedum plumbizincicola seedlings, control the environmental temperature at 23°C. When the environmental temperature is lower than 23°C, build a greenhouse to control the environmental temperature of the Sedum plumbizincicola seedlings at 23°C. When the environmental temperature is higher than 23°C, build a shading net to control the growth environmental temperature of the Sedum plumbizincicola seedlings at 23°C, and conduct field management regularly.

[0054] Among them, in Step 2, the Sedum plumbizincicola seedlings are transplanted at a planting density of 15 cm × 15 cm. At the same time, it should be noted that the field management includes irrigation, drainage, topdressing, pest control, and weeding. Pest control adopts conventional agricultural control methods, topdressing adopts the application of commercially available organic fertilizers, and weeding should adopt special herbicides for Sedum plumbizincicola and manual weeding methods.

[0055] Step 3: When there is no obvious growth in the branches of Sedum plumbizincicola within 15 - 20 days and its biomass has reached the maximum value, harvest the Sedum plumbizincicola and remove the harvested materials from the field.

[0056] Example 2: The difference between this example and Example 1 is that in Step 1, the Sedum plumbizincicola branches are raised in a temperature environment of 8°C for 30 days.

[0057] Example 3: The difference between this example and Example 1 is that in Step 1, the Sedum plumbizincicola branches are raised in a temperature environment of 25°C for 90 days.

[0058] Example 4: The difference between this example and Example 1 is that in Step 2, during the growth period of the Sedum plumbizincicola seedlings, control the environmental temperature at 8°C. When the environmental temperature is lower than 8°C, build a greenhouse to control the environmental temperature of the Sedum plumbizincicola seedlings at 8°C. When the environmental temperature is higher than 8°C, build a shading net to control the growth environmental temperature of the Sedum plumbizincicola seedlings at 8°C.

[0059] Example 5: The difference between this example and Example 1 is that in Step 2, during the growth period of the Sedum plumbizincicola seedlings, control the environmental temperature at 30°C. When the environmental temperature is lower than 30°C, build a greenhouse to control the environmental temperature of the Sedum plumbizincicola seedlings at 30°C. When the environmental temperature is higher than 30°C, build a shading net to control the growth environmental temperature of the Sedum plumbizincicola seedlings at 30°C.

[0060] To explore the critical temperature of vernalization of Sedum plumbizincicola, the following experiment is designed:

[0061] 1) Test materials: The tested Sedum plumbizincicola seedlings are collected from Zhehai Town, Huize County, Qujing City, Yunnan Province. The tested contaminated soil is collected from Guilin Town, Shexian County, Anhui Province. The soil pH is 8.14, and the total amounts of Cd and Zn are 6.21 mg·kg-1 and 280 mg·kg -1 ;

[0062] 2) Experimental design and implementation: The pot experiment was conducted in the greenhouse of the 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 Sedum plumbizincicola seedlings with consistent growth were selected and placed in a constant temperature and light growth chamber for cultivation. Three temperature treatments of 4 °C, 8 °C, and 12 °C were set, and the treatment times for the three temperature treatments were set to 14, 21, 28, 35, 42, 49, and 56 d respectively, for a total of 7 different cultivation time periods. In addition, three treatments were also set, namely, the treatment of always outdoor normal temperature in winter, the treatment of always 23 °C in the constant temperature and light growth chamber (control), and the treatment of being cultured at 4 °C until April 23, 2024 (123 d) and then transferred to the normal temperature environment. There were a total of 24 experimental treatments, with 3 replicates for each treatment. Each treatment included 8 Sedum plumbizincicola plants, and the different treatment experiments all started on December 22, 2023. After the cultivation time of the 7 different time periods in the low-temperature treatment group ended, the potted plants were transferred to a constant temperature and light growth chamber at 23 °C for continued cultivation. After the flower buds appeared, the flowering situation of Sedum plumbizincicola was observed every day, the number of flowers was counted, and the flowering rate was calculated. 0.05 g of urea and 0.05 g of potassium dihydrogen phosphate were applied to each pot as basal fertilizers, and on March 5, 2024, 0.025 g of urea and potassium dihydrogen phosphate were top-dressed to each pot. Water was watered every day to ensure the water required for the growth of Sedum plumbizincicola;

[0063] 3) Sample collection and treatment: Since the Sedum plumbizincicola in the 8 °C and 12 °C treatment groups did not show the vernalization phenomenon, four treatments, namely, the treatment of always outdoor normal temperature in winter, the treatment of always 23 °C (CK), the treatment of 4 °C for 123 d, and the treatment of 4 °C for 56 d, were selected for sampling on April 23, 2024, and June 20, 2024. These two time points were 16 d before flowering and the full-bloom period of Sedum plumbizincicola treated at 4 °C for 56 d, as well as the pre-flowering and full-bloom periods of the treatment of always outdoor normal temperature in winter and the treatment of 4 °C for 123 d. Although the treatment of always 23 °C (CK) did not flower, plant samples were also taken at the same time. 1-2 true leaves close to the shoot tip of Sedum plumbizincicola and part of the shoot tip were collected. Part of the fresh samples were chopped and mixed for the determination of physiological and biochemical indexes; another part of the fresh samples were washed with deionized water, dried, blanched at 105 °C for 20 min, and then dried to a constant weight at 70 °C and pulverized for use. The last batch of samples was harvested on July 2, 2024, and the above-ground parts of Sedum plumbizincicola were collected, washed with tap water and deionized water respectively, blanched, dried, and weighed;

[0064] 4) Determination methods:

[0065] Flowering index: The calculation formula for the flowering rate of each treatment is: Flowering rate (%) = Number of flowering plants / Total number of plants × 100; Initial flowering date: The date when the first plant in the population starts to flower;

[0066] Physiological and biochemical indexes: The determination was carried out according to the methods in "Principles and Techniques of Plant Physiological and Biochemical Experiments". The contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids were determined by the 95% ethanol grinding extraction method, the content of malondialdehyde was determined by the thiobarbituric acid (TBA) method, the anthrone colorimetric method was used for the determination of soluble sugar and starch contents, the Coomassie brilliant blue G-250 method was used for the determination of soluble protein content, and the Kjeldahl method was used for the determination of total N content. The contents of indexes such as chlorophyll, soluble sugar, malondialdehyde soluble sugar and starch are all the contents 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);

[0067] Determination of growth indexes: At the time of experimental harvest, a steel ruler with a precision of 0.1 mm was used to measure the plant height of Sedum plumbizincicola, a vernier caliper with a precision of one-thousandth was used to measure the stem diameter of Sedum plumbizincicola, and an electronic balance with a precision of one-thousandth was used to weigh the dry weight of the Sedum plumbizincicola sample;

[0068] Data processing and analysis: Excel 2010 and SPSS 19.0 software were used for correlation analysis of the data, the least significant difference method (LSD) was used for significant difference test (p < 0.05), and graphs were drawn through Origin 2021 software;

[0069] 5) Results and analysis

[0070] Effects of different temperature and duration treatments on the flowering of Sedum plumbizincicola:

[0071] As shown in Table 1, no flowering phenomenon occurred in the Sedum plumbizincicola in the treatment groups of 8 °C, 12 °C and 23 °C (CK) after being cultured for different periods, while flowering phenomenon occurred in the Sedum plumbizincicola after being treated at 4 °C for 35 - 56 d. For the Sedum plumbizincicola transferred to the 23 °C growth chamber after being treated at 4 °C for 56 d, the first flowering plant was observed on May 9, 2024 (the 83rd d), and the flowering rate had reached over 90.0% after 94 days. The first flowering date of the Sedum plumbizincicola treated at outdoor normal temperature in winter was June 14, 2024, which was 36 d later than that of the experimental group treated at 4 °C for 56 d. In addition, with the extension of the 4 °C low-temperature treatment time (35 - 56 days), the first flowering date of Sedum plumbizincicola was advanced and the flowering rate increased. The flowering rates at 49 d and 56 d of low-temperature treatment both reached 100%. Therefore, the critical temperature for vernalization of Sedum plumbizincicola is between 4 - 8 °C. Vernalization phenomenon occurred after being treated at 4 °C for 35 d, and full vernalization had occurred at 49 d.

[0072] Table 1 Effects of Different Temperatures and Their Durations on the Flowering Rate and First Flowering Date of Sedum plumbizincicola

[0073] ;

[0074] Among them, the values in Table 1 are the mean ± standard deviation.

[0075] Results of the effects of different temperatures and their durations on the aboveground growth of Sedum plumbizincicola:

[0076] Table 2 lists the changes in stem diameter, plant height, and aboveground biomass of Sedum plumbizincicola at the full-bloom stage under different temperature and duration treatments. After treatment at 4 °C for 14 d, 21 d, or 28 d, there were no significant differences in the stem diameter and plant height of Sedum plumbizincicola compared with those treated at 8 °C and 12 °C for the same cultivation time; after treatment at 4 °C for 35 d, 42 d, 49 d, or 56 d, compared with the normal temperature treatment group, the stem diameter and plant height of Sedum plumbizincicola were significantly higher than those treated at 8 °C and 12 °C for the same cultivation time, and also significantly higher than those in the group treated at 23 °C (CK) all the time. After Sedum plumbizincicola was treated at 4 °C, 8 °C, and 12 °C for a certain period of time and then placed at 23 °C, the plants could grow normally and the survival rate reached 100%. Under the condition of the same treatment time (35 - 56 d), there were no significant differences in the aboveground biomass of Sedum plumbizincicola treated at 4 °C compared with those treated at 8 °C, 12 °C, and 23 °C (CK), but the aboveground biomass of Sedum plumbizincicola treated at normal outdoor temperature in winter was significantly lower than that of other temperature treatments. With the extension of the low-temperature treatment time, the stem diameter and plant height of Sedum plumbizincicola treated at 4 °C showed a significant increasing trend, but the difference in the aboveground biomass of Sedum plumbizincicola did not reach a significant level.

[0077] Table 2 Effects of Different Temperatures and Their Durations on the Growth of Sedum plumbizincicola at the Full-Bloom Stage

[0078] ;

[0079] Among them, different capital letters in the same column of Table 2 indicate significant differences (p < 0.05), and different lowercase letters in the same row indicate significant differences (p < 0.05).

[0080] Results of the effects of different temperatures and their durations on the chlorophyll content of Sedum plumbizincicola leaves:

[0081] Figures 1 - 4The changes in the contents of chlorophyll and carotenoids in the leaves of Sedum plumbizincicola under different temperature treatments before flowering and at the full flowering stage are presented. Compared with before flowering, the contents of chlorophyll a, chlorophyll b, and total chlorophyll in the plants under the treatments of constant outdoor temperature, 4 °C for 56 days, and 4 °C for 123 days all significantly decreased at the full flowering stage. However, there was no significant change in the chlorophyll content of Sedum plumbizincicola plants under the treatment of constant 23 °C (CK) at the full flowering stage. Compared with the treatment of constant 23 °C (CK), the treatment of 4 °C for 56 days had no significant effect on the contents of chlorophyll a, chlorophyll b, and total chlorophyll in Sedum plumbizincicola before flowering, but significantly reduced the contents of chlorophyll a, chlorophyll b, and total chlorophyll at the full flowering stage by 50.3%, 41.8%, and 47.4%, respectively. However, the contents of chlorophyll a, chlorophyll b, and total chlorophyll in Sedum plumbizincicola under the treatment of 4 °C for 123 days all significantly decreased, with significant decreases of 25.1%, 24.5%, and 24.9% before flowering and 69.1%, 51.1%, and 62.8% at the full flowering stage. Compared with the treatment of constant 23 °C (CK), the contents of carotenoids at the full flowering stage under the treatments of 4 °C for 56 days and 123 days significantly increased by 25.9% and 32.2%, respectively. Therefore, the 4 °C treatment significantly reduces the chlorophyll content, and this is more significant at the full flowering stage. After the 4 °C treatment duration increased from 56 days to 123 days, the chlorophyll content before flowering also significantly decreased.

[0082] Results of the effects of different temperatures and their durations on the malondialdehyde (MDA) content in the leaves of Sedum plumbizincicola:

[0083] As Figure 5 can be seen, there was no significant difference in the malondialdehyde (MDA) content in the leaves of Sedum plumbizincicola before flowering and at the full flowering stage under different temperature treatment conditions. Compared with the treatment group of constant 23 °C (CK), the MDA content in the leaves of Sedum plumbizincicola under the treatments of 4 °C for 56 days, 4 °C for 123 days, and constant outdoor temperature significantly increased by 22.4%, 41.9%, and 71.2% before flowering and 25.6%, 40.2%, and 52.6% at the full flowering stage (p < 0.05).

[0084] Results of the effects of different temperatures and their durations on the carbon and nitrogen metabolism in the leaves of Sedum plumbizincicola:

[0085] From Figures 6 - 10It can be seen that the contents of soluble sugar and starch in the leaves of Sedum plumbizincicola in the 23 °C treatment group (CK) were significantly higher in the early flowering stage than in the full flowering stage, while the contents of soluble sugar and starch in the leaves treated at room temperature outdoors and 4 °C for 56 d were significantly higher in the full flowering stage than in the early flowering stage. Compared with before flowering, the soluble protein content in the leaves of Sedum plumbizincicola under different temperature treatments increased significantly in the full flowering stage, while the total nitrogen content in the leaves decreased significantly. By calculating the total sugar / total nitrogen (C / N), it was found that the C / N ratios of the leaves in the three low-temperature treatment groups at room temperature outdoors, 4 °C for 56 d, and 4 °C for 123 d were significantly higher in the full flowering stage than before flowering, while the C / N ratio of the leaves in the 23 °C treatment group decreased significantly with the increase of growth time.

[0086] Compared with the 23 °C treatment group (CK), there were no significant differences in the contents of soluble sugar, starch, soluble protein, and total nitrogen in the leaves of Sedum plumbizincicola treated at 4 °C for 56 d in the early flowering stage, but the contents of soluble sugar, starch, and soluble protein in the leaves increased significantly in the full flowering stage, while the total nitrogen content decreased significantly. In the full flowering stage, the contents of soluble sugar, starch, and soluble protein in the leaves treated at room temperature outdoors and 4 °C for 123 d were also significantly higher than those in the 23 °C treatment group (CK), while the total nitrogen content in the leaves was significantly lower than that in the 23 °C treatment group (CK). Further analysis found that the C / N of the leaves of Sedum plumbizincicola in the three low-temperature treatment groups at room temperature outdoors, 4 °C for 56 d, and 4 °C for 123 d was also significantly higher than that in the 23 °C treatment group in the full flowering stage. Therefore, compared with non-vernalized plants, the vernalization phenomenon induced by low temperature will significantly increase the contents of soluble sugar, starch, and soluble protein in the leaves of Sedum plumbizincicola in the full flowering stage, but will decrease the total nitrogen content in the leaves, thereby increasing the C / N.

[0087] The removal effect of Sedum plumbizincicola on soil cadmium:

[0088] Table 3 lists the effects of Sedum plumbizincicola planting on the removal amount of soil Cd after 56 d of different temperature treatments. After treatment at 4 °C for 56 d, the Cd removal amount of Sedum plumbizincicola was significantly lower than that of other temperature treatments; there were no significant differences among the temperature treatments of 23 °C (CK), 12 °C, 8 °C, and the room temperature group, but the room temperature group had higher temperature requirements in heat preservation control compared with the CK group. Therefore, the comprehensive effect of the Sedum plumbizincicola treatment in the CK group was better.

[0089] Table 3 Effects of Sedum plumbizincicola on the removal amount of Cd in soil after 56 d of different temperature treatments

[0090] ;

[0091] Example 6: The difference between this example and Example 1 is that in step 2, the Sedum plumbizincicola seedlings were transplanted at a planting density of 12 cm × 12 cm.

[0092] Example 7: The difference between this example and Example 1 is that in step 2, the Sedum plumbizincicola seedlings are transplanted at a planting density of 25 cm × 25 cm.

[0093] To verify the removal effect of the above treatment on cadmium in the soil by Sedum plumbizincicola, a rectangular plot with a length × width of 10 m × 6 m was set up to simulate the planting density. Using the above test method, the removal amount of Cd in each example was measured, and the results are shown in Table 4 below:

[0094] Table 4 Effect of different remediation methods on the removal of Cd in the soil by Sedum plumbizincicola after 56 days

[0095] ;

[0096] Table 4 lists the removal effects of Sedum plumbizincicola planting on Cd in the soil under different treatment processes. After changing the planting density of Sedum plumbizincicola seedlings, there were obvious changes in the Cd removal amount. In Example 6, when the planting density decreased, the Cd removal amount decreased. This may be due to the insufficient Cd absorption caused by the too sparse planting density, resulting in a decrease in the Cd removal amount. In Example 7, when the planting density increased, the Cd removal amount also decreased. This may be due to the excessive competition between plants caused by the too dense planting density, thus affecting the enrichment of Cd in the soil by Sedum plumbizincicola.

[0097] Example 8: The difference between this example and Example 1 is that in step 2, before the Sedum plumbizincicola seedlings are planted in the cadmium-contaminated soil, the cadmium-contaminated soil is plowed and fertilized. The plowing and fertilization method is as follows:

[0098] The agricultural waste fermentate is applied to the cadmium-contaminated soil at a rate of 1300 kg / mu, and then plowed. After the cadmium-contaminated soil is plowed, it is covered with a film for 1.5 days, and then the Sedum plumbizincicola seedlings are transplanted into the cadmium-contaminated soil. Since it is in the south, the agricultural waste fermentate described in this example is obtained by fermenting agricultural waste, and the agricultural waste is crops planted in local non-polluted areas, selected from rice straw.

[0099] Among them, the preparation method of the agricultural waste fermentate is as follows:

[0100] 1) Build a fermentation frame with a height of 5 m, a width of 2.5 m, and a length of 2.5 m. Cut the agricultural waste into pieces of 4 cm and lay it in layers in the fermentation frame. The laying thickness of each layer of agricultural waste is 25 cm.

[0101] 2) After each layer of agricultural waste is filled, spray water at 13 °C on each layer of agricultural waste to keep the moisture content of the agricultural waste at 45%. Then evenly spray the composite bacterial slurry, and the spraying thickness of the composite bacterial slurry is 4 cm.

[0102] 3) After the agricultural waste is laid in layers and filled, ferment for 4 d to obtain the fermented agricultural waste.

[0103] Among them, the composite bacterial slurry is obtained by mixing the composite bacterial material and water at 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 4 W / cm 2 , the frequency is 25 kHz, and the time is 12 min; by mass, the composite bacterial material is composed 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; among them, the straw powder is a powder obtained by ball-milling rice straw or corn straw through an 80-mesh sieve.

[0104] Example 9: The difference between this example and Example 8 is that the fermented agricultural waste is applied to the cadmium-contaminated soil at 800 kg / mu, and then plowed. After plowing the cadmium-contaminated soil, the cadmium-contaminated soil is covered with a film for 1 d.

[0105] Example 10: The difference between this example and Example 8 is that the fermented agricultural waste is applied to the cadmium-contaminated soil at 1500 kg / mu, and then plowed. After plowing the cadmium-contaminated soil, the cadmium-contaminated soil is covered with a film for 2 d.

[0106] Example 11: The difference between this example and Example 8 is that a fermentation frame with a height of 4 m, a width of 2 m, and a length of 2 m is constructed. The agricultural waste is cut into pieces of 3 cm and laid in layers in the fermentation frame, and the laying thickness of each layer of agricultural waste is 20 cm.

[0107] Example 12: The difference between this example and Example 8 is that a fermentation frame with a height of 6 m, a width of 3 m, and a length of 3 m is constructed. The agricultural waste is cut into pieces of 5 cm and laid in layers in the fermentation frame, and the laying thickness of each layer of agricultural waste is 30 cm.

[0108] Example 13: The difference between this example and Example 8 is that water at 10 °C 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. The spraying thickness of the composite bacterial slurry is 2 cm. After the agricultural waste is laid in layers and filled, ferment for 3 d.

[0109] Example 14: The difference between this example and Example 8 is that water at 15 °C 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. The spraying thickness of the composite bacterial slurry is 5 cm. After the agricultural waste is laid in layers and filled, ferment for 5 d.

[0110] Example 15: The difference between this example and Example 8 is that the composite bacterial slurry is obtained by mixing the composite bacterial material and water at 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 2 W / cm 2 , the frequency is 20 kHz, and the time is 5 min.

[0111] Example 16: The difference between this example and Example 8 is that the composite bacterial slurry is obtained by mixing the composite bacterial material and water at 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 5 W / cm 2 , the frequency is 30 kHz, and the time is 15 min.

[0112] Example 17: The difference between this example and Example 8 is that, 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; among them, the straw powder is a powder obtained by ball-milling rice straw through a 50-mesh sieve.

[0113] Example 18: The difference between this example and Example 8 is that, 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; among them, the straw powder is a powder obtained by ball-milling rice straw through a 100-mesh sieve.

[0114] To verify the effect of the above treatment on the removal of cadmium from soil by Sedum plumbizincicola, the above test method was used to measure the removal amount of Cd in each example, and the results are shown in Table 5 below:

[0115] Table 5 Effects of different remediation methods on the removal of Cd from soil by Sedum plumbizincicola after 56 days

[0116] ;

[0117] Table 5 lists the removal amounts of Cd from soil by Sedum plumbizincicola under different treatment processes. After landfilling and plowing with agricultural waste fermented products, the removal amounts of Cd from Cd-polluted soil by Sedum plumbizincicola have all increased to a certain extent;

[0118] In Example 9, after changing the landfill amount of agricultural waste fermented products and the film covering time, the Cd removal amount decreased. This may be because the landfill amount of agricultural waste fermented products was too small to achieve the ideal use effect. In Example 10, after changing the landfill amount of agricultural waste fermented products and the film covering time, the Cd removal amount did not change significantly. This may be because the landfill amount of agricultural waste fermented products has tended to be saturated;

[0119] In Examples 11 and 12, after changing the paving specifications and thickness of agricultural waste, the Cd removal amount decreased. This may be because different single-layer paving thicknesses of agricultural waste affected the preparation effect of the agricultural waste ferment, thereby affecting the use performance of the agricultural waste ferment;

[0120] In Examples 13 and 14, after changing the addition amount of the composite bacterial slurry and the water content, the Cd removal amount decreased. This may be because different sprinkling water temperatures and the usage amount of the composite bacterial slurry affected the preparation effect of the agricultural waste ferment. After the addition amount of the composite bacterial slurry was too large, it was easy to pre-release a large amount of heat during the fermentation process of the agricultural waste ferment, thereby affecting the subsequent use effect when landfilled into cadmium-contaminated soil. When the addition amount of the composite bacterial slurry was too small, the use performance of the agricultural waste ferment decreased;

[0121] In Example 15, after changing the preparation conditions of the composite bacterial material, the Cd removal amount decreased. This may be because the amount of the composite bacterial material in the composite bacterial slurry was small and the mixing was insufficient, resulting in an unsatisfactory use effect. In Example 16, after changing the preparation conditions of the composite bacterial material, the Cd removal amount did not change significantly. This may be because the amount of the composite bacterial material in the composite bacterial slurry and the mixing had reached saturation;

[0122] In Examples 17 and 18, after changing the composition of the composite bacterial material, the Cd removal amount decreased. This may be because different compositions of the composite bacterial material affected the use effect of the composite bacterial slurry, thereby affecting the use performance of the agricultural waste ferment.

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 unvernalized Sedum serrata seedlings; wherein the anti-vernalization treatment is: raising the branches of Sedum serrata in a critical temperature environment of 8°C for 56 days; Step 2: Subsequently, the unvernalized Sedum sedum seedlings are transplanted into cadmium-contaminated soil. During the planting and growth period of the Sedum sedum seedlings, the ambient temperature is controlled at 8-30° C., and field management is performed regularly; Step 3, when the branches of the Sedum serrata have no obvious growth within 15 to 20 days, the Sedum serrata is harvested and the harvest is removed from the field; In step 2, before the unvernalized 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: Apply 800-1500 kg / mu of fermented agricultural waste to cadmium-contaminated soil, followed by tillage; 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; 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, ferment it for 3-5 days to obtain the fermented agricultural waste; 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.

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: 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.

6. The method for remediating cadmium-contaminated soil according to claim 5, 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.

Images