Silicon-iron modified biomass charcoal for reducing cadmium and arsenic absorption of rice and application of silicon-iron modified biomass charcoal

Abstract

The invention belongs to the technical field of agricultural planting, and particularly relates to silicon-iron modified biomass charcoal for reducing cadmium and arsenic absorption of rice and application of the silicon-iron modified biomass charcoal. The silicon-iron modified biomass charcoal is obtained by mixing and pyrolyzing magnetic charcoal and silicate; according to the silicon-iron modified biomass charcoal, the content of Cd and As in soil pore water is changed, the effectiveness of Cd and As in soil is reduced, the content of iron plaque on the root surface of a rice root system is increased, and the expression quantity of Cd and As transporter protein is regulated and controlled, so that the absorption of rice to cadmium and arsenic is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of agricultural planting, and in particular relates to a silicon-iron modified biomass carbon material for reducing the absorption of cadmium and arsenic by rice and an application thereof. Background Art

[0002] In addition to directly polluting drinking water, heavy metals in water bodies also affect surrounding soils through surface runoff, sewage irrigation and other agricultural activities and industrial production methods, resulting in increased heavy metal content in the soil. However, excessive heavy metal content in the soil causes rice to absorb a large amount of heavy metals during its growth and accumulate in its grains, seriously affecting human health. In addition, arsenic and cadmium in the soil can seriously affect the growth of rice, causing a decrease in rice plant height and dry weight, which in turn affects rice yields.

[0003] The existing technology uses magnetic biochar as an adsorption material for adsorbing arsenic and cadmium in water bodies to achieve water body repair. The magnetic biochar is obtained by mixing a magnetite suspension prepared from iron ions with different ionic valence states with plant straw and then pyrolyzing it. If it is directly applied to the soil to adsorb arsenic and cadmium, it will inhibit the growth of rice. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a silicon-iron modified biomass carbon material for reducing the absorption of cadmium and arsenic by rice and its application, which can effectively reduce the absorption of cadmium and arsenic by rice and reduce the content of cadmium and arsenic accumulation in grains.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] The first aspect of the present invention provides a silicon-iron modified biochar for reducing the absorption of cadmium and arsenic by rice, wherein the silicon-iron modified biochar is obtained by mixing and pyrolyzing magnetic biochar and silicate; the magnetic biochar is obtained by mixing a magnetite suspension with plant straw; The silicon-iron modified biochar is used to oxidize Fe in soil 2+ , forming an iron film on the surface of rice roots to reduce the absorption of cadmium and arsenic by rice; The mass of the silicate accounts for 0.5% to 1% of the mass of the magnetic biochar.

[0007] The silicon-iron modified biochar in the present invention can significantly reduce the Cd and As content in various parts of rice at the jointing and maturity stages. By adding 5% to 6% of the mass of magnetic biochar, silicates are added to oxidize the iron ions in the soil and form an iron film on the surface of the rice root system to reduce the absorption of cadmium and arsenic by rice; and by controlling the amount of silicate added, the adsorption capacity of Cd can be further improved. Too much or too little silicate addition will affect the adsorption capacity of Cd. The silicon-iron modified biochar in the present invention achieves the purpose of reducing the absorption of cadmium and arsenic by rice through four ways: changing the content of Cd and As in pore water, reducing the effectiveness of Cd and As in the soil, increasing the content of iron film on the root surface of rice roots, and regulating the expression of Cd and As transport proteins. After the wheat grains were repaired, the Cd and As contents were 0.13 mg·kg -1 and 1.79 mg kg -1 , both lower than the national standard GB2762-2017.

[0008] In another preferred embodiment, the silicate is CaSiO3.

[0009] In another preferred embodiment, the particle size of the silicon-iron modified biochar is 1 μm to 100 μm. The smaller the particle size, the easier it is to react with cadmium and arsenic in the soil to fix them. However, because the density of biochar is low, if the particles are too small, they will float to the surface of the water when planted in flooded conditions, affecting the repair of Cd and As in the soil.

[0010] In another preferred embodiment, the pyrolysis temperature is 700° C. to 720° C., and the insulation time is 2 h to 2.5 h.

[0011] In another preferred embodiment, the pyrolysis is carried out in an inert gas atmosphere.

[0012] In another preferred embodiment, the inert gas is nitrogen.

[0013] In another preferred embodiment, the specific process of obtaining the magnetic biochar is as follows: The plant straw and the magnetite suspension are mixed in a mass volume ratio of 20 kg: 400 L to 410 L, the pH is adjusted to 11 to 12, the mixture is reacted at 60° C. to 65° C. for 2 h to 2.5 h, the mixture is allowed to stand, and the mixture is filtered to obtain the magnetically modified biochar; The magnetite suspension is obtained by mixing FeSO4 and FeCl3 in a molar ratio of 1:1.8-2 and causing a coprecipitation reaction in water.

[0014] The second aspect of the present invention provides the use of the silicon-iron modified biochar in the preparation of a soil passivator.

[0015] In another preferred embodiment, the soil passivator is used to adjust the pH of rhizosphere soil, reduce the concentration of Cd and As in soil pore water, and reduce the content of available Cd and As in soil.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The silicon-iron modified biomass carbon material of the present invention is prepared by adding silicate to magnetic biochar, and the SiO3 in the silicate is 2- Hydrolysis to form H2SiO3 can oxidize Fe in the soil 2+ Fe 3+ , forming more iron oxides loaded on the surface of rice roots and forming an iron film on the root surface. The iron film on the root surface has the function of adsorbing and intercepting heavy metals, thereby effectively reducing the absorption of cadmium and arsenic by rice.

[0017] The use of the silicon-iron modified biochar in the present invention can reduce the content of heavy metals Cd and As in the soil pore water during the jointing and maturity stages. The heavy metals in the pore water are the most active and most easily absorbed and utilized by plants. Therefore, the silicon-iron modified biochar reduces the content of heavy metals Cd and As in the soil pore water, thereby reducing the accumulation of Cd and As in rice grains. The effective content of heavy metals in the soil reflects the ability of rice to absorb and utilize them, and the silicon-iron modified biochar reduces the effective content of Cd and As in the soil by changing the physical and chemical properties and adsorption methods, thereby reducing the absorption of Cd and As by rice. In addition, by adding the silicon-iron modified biochar in this application, the expression level of Cd and As transport proteins in rice can be regulated, which significantly reduces the Fe transport protein. OsIRT1 , Cd transporter OsNramp1 and OsNramp2 , As transporter OsL and OsLsi2 The expression level in rice plants reduces the absorption of Cd and As by rice and reduces the transport of Cd and As. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The results of pH value of rhizosphere and non-rhizosphere soil at different rice stages are shown in Figure 1. (a) is the results of pH value of rhizosphere and non-rhizosphere soil at the jointing stage, and (b) is the results of pH value of rhizosphere and non-rhizosphere soil at the maturity stage. In the figure, a, b, c, and d represent different significant differences compared with the blank group (P<0.05).

[0019] Figure 2 The following are the results of DOC content in rhizosphere and non-rhizosphere soil at different rice stages. (a) is the result of DOC content in rhizosphere and non-rhizosphere soil at jointing stage; (b) is the result of DOC content in rhizosphere and non-rhizosphere soil at maturity stage.

[0020] Figure 3Figure 2 is a graph showing the changes in Cd and As concentrations in soil pore water over time. (a) is a graph showing the changes in Cd concentration in soil pore water over time; (b) is a graph showing the changes in As concentration in soil pore water over time.

[0021] Figure 4 The figures show the contents of available Cd and As in the rhizosphere and non-rhizosphere soils at different rice growing stages; (a) shows the contents of available Cd in the rhizosphere and non-rhizosphere soils at the jointing stage; (b) shows the contents of available Cd in the rhizosphere and non-rhizosphere soils at the maturity stage; (c) shows the contents of available As in the rhizosphere and non-rhizosphere soils at the jointing stage; (d) shows the contents of available As in the rhizosphere and non-rhizosphere soils at the maturity stage.

[0022] Figure 5 The results of rice plant height and dry weight content at different rice stages are shown in Figure 2. (a) shows the results of rice plant height and dry weight content at the jointing stage; (b) shows the results of rice plant height and dry weight content at the maturity stage.

[0023] Figure 6 The following are the results of Cd and As content in different parts of rice at different rice growing stages; (a) is the results of Cd content in various parts of rice at the jointing stage; (b) is the results of As content in various parts of rice at the jointing stage; (c) is the results of Cd content in various parts of rice at the maturity stage; (d) is the results of As content in various parts of rice at the maturity stage.

[0024] Figure 7 The results of transporter protein expression at different rice stages; (a) at the jointing stage OsIRT1 The expression results of transporter proteins; (b) is the jointing stage OsNramp5 The expression results of transporter proteins; (c) is the jointing stage OsNramp1 Transporter protein expression results; (d) is the mature stage OsNramp1 The expression results of transporter proteins; (e) is the mature stage OsNramp5 The expression results of transporter proteins; (f) is the mature stage OsNramp1 Transporter protein expression results.

[0025] Figure 8 For different periods OsL and OsLsi2 The expression results of transporter proteins; (a) is the jointing stage OsL The expression results of transporter proteins; (b) is the jointing stage OsLsi2 The expression results of transporter proteins; (c) is the mature stage OsL Transporter protein expression results; (d) is the mature stage OsLsi2 Transporter protein expression results. DETAILED DESCRIPTION

[0026] The following will be combined with the specific implementation of the present invention to clearly and completely describe the technical solution in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The methods described in the embodiments of the present invention are conventional methods unless otherwise specified. The materials, reagents, etc. used can be obtained from commercial sources unless otherwise specified.

[0028] The following is a detailed description of a silicon-iron modified biochar for reducing the absorption of cadmium and arsenic by rice and its application.

[0029] Example 1 A silicon-iron modified biomass charcoal for reducing the absorption of cadmium and arsenic by rice is prepared by the following steps: S1, FeSO4·7H2O and FeCl3·6H2O were dissolved in water, and a coprecipitation reaction occurred to obtain a magnetite suspension; wherein the initial concentration of FeSO4 was 0.1 mol / L, and the initial concentration of FeCl3 was 0.2 mol / L.

[0030] S2, 20g rice straw was ground through a 1mm sieve and then evenly mixed with 400mL of magnetite suspension, and 5mol·L -1 The NaOH solution was added to adjust the pH value to 11, and the mixture was stirred and reacted at 65°C in a water bath for 2.5 hours. The mixture was allowed to stand for 24 hours, and the precipitate was filtered and dried to obtain the dried magnetic modified biochar.

[0031] S3. The dried magnetically modified biochar was mixed with CaSiO3, wherein the mass of CaSiO3 accounted for 5% of the mass of the magnetically modified biochar. The mixture was placed in a muffle furnace and pyrolyzed at 700°C in a nitrogen atmosphere for 2 hours. The mixture was then ground in a ball mill for 1.5 hours to obtain silicon-iron modified biochar with a particle size of 100 μm.

[0032] Example 2 Effects of Silicon-Iron Modified Biochar on Cadmium and Arsenic Uptake by Rice 1. Test soil and rice varieties The rice variety was Zhongzheyou No. 1; the test soil was collected from Cd-As composite contaminated soil around the mining area in Shangyu District, Shaoxing City, Zhejiang Province. The soil was collected from 0-20 cm on the surface according to the plum blossom distribution method, and then naturally dried and crushed through a 10-mesh sieve for later use. The basic physical and chemical properties of the test soil and the total amount of Cd and As are shown in Table 1.

[0033] Table 1 Physical and chemical properties of experimental soil and total concentrations of Cd and As Note: In the table, sand (%) means the percentage of sand mass to soil mass, silt (%) means the percentage of silt mass to soil mass, and clay (%) means the percentage of clay mass to soil mass.

[0034] 2. Different treatment methods A rice pot experiment was carried out in a constant temperature greenhouse. The silicon-iron modified biochar, biochar and magnetic biochar in Example 1 were used as soil passivators, mixed into rice-growing soil in different masses, and 3 repetitions were set for each treatment. Among them, the biochar is obtained by pyrolysis of rice straw, and the magnetic modified biochar is the magnetic modified biochar in Example 1. The specific settings are shown in Table 2. Spraying foliar silicon fertilizer is a conventional agronomic means for reducing cadmium in rice. The purpose of spraying foliar silicon fertilizer is to compare the effects of the present invention with conventional agronomic cadmium reduction measures. The foliar silicon fertilizer was purchased from Lanlu liquid silicon fertilizer, and the application amount was the same as that of silicon-iron modified biochar.

[0035] Table 2 Different treatment groups Weigh 4 kg (excluding the weight of the flower pot) of air-dried soil sample that has passed through a 10-mesh sieve, mix the above 11 groups of soil passivators evenly into the soil, place it in a plastic pot without air holes, and add appropriate amount of water to achieve a soil moisture content of 60% of the field and water holding capacity. Apply 0.2 g kg urea during the water balance period. -1 , potassium dihydrogen phosphate 0.1 g·kg -1 . When the material and the soil achieve a stable equilibrium state. The rice seedlings are transplanted into pots, and the water is continuously flooded for 15 days after transplanting. Subsequently, the dry-wet alternating irrigation method is used during the physiological growth period to ensure that a 3cm~4cm moist layer is maintained on the soil surface. After the soil is naturally dried to no obvious signs of water accumulation, the next round of irrigation is carried out. The cycle of this process is controlled within 10 days to 15 days. The water supply needs to be suspended 10 days before the harvest stage. Starting from the 10th day after rice transplantation, a pore water collector is implanted in the area near the root of the rice, and then the pore water is sampled every 10 days to measure the concentrations of cadmium and arsenic in the soil pore water. Rice plant samples, rhizosphere soil and non-rhizosphere soil samples were destructively collected at the jointing stage and maturity stage of rice to measure soil physical and chemical properties such as pH and DOC content, soil pore water concentration and effective Cd and As content, total amount of Cd and As in various parts of rice, and expression of Cd and As transporters.

[0036] 3. Analysis methods 1) Determination of soil physicochemical properties: Soil pH (soil-water ratio 1:2.5, oscillation 2h) was measured using a pH meter (SevenExcellence Cond meterS700, Mettler Toledo, Switzerland), and soil DOC content (soil-water ratio 1:5, extraction 1h) was measured using a TOC analyzer (TOC-L CPN, Shimadzu, Japan). The available states of Cd(Ⅱ) and As(Ⅲ) were measured using 0.01mg·L -1 CaCl2 (1:10 soil-water ratio, leaching for 2 h) and 0.05 mg·L -1 The extraction was carried out with NH4H2PO4 (1:25 soil-water ratio, extraction for 16h).

[0037] 2) Determination of root surface iron film: DCB (dithionite-citrate-bicarbonate) was used to extract the root surface iron film. 0.6 g of rice roots were placed in a beaker, and 40 mL of DCB (a mixed solution of 0.03 mol·L-1 Na3C6H5O7·Na2O, 0.06 mol·L-1 Na2S2O4 and 0.125 mol·L-1 NaHCO3) solution was added. The roots were soaked at room temperature for 0.5 h, and the remaining iron-free part was removed. The roots were thoroughly washed with deionized water and then dried at 60 °C until constant weight (recorded as m1). The iron film content = (0.6–m1) × 1000 / 0.6 mg·kg -1 .

[0038] 3) In the experiment, the total amount of Cd and As in rice tissue was determined by nitric acid digestion method: 0.1g dry rice sample was weighed into a test tube, 10mL of high-grade pure concentrated HNO3 was added, a bent-neck funnel was placed on the bottle mouth and left overnight, and the small funnel was removed after digestion at 150℃ for 2h, and then the solution was boiled until it was clear or light green with only 1mL of a small amount, and then the volume was made up to 50mL with 5% mass percentage HNO3 (high-grade pure) for testing. Cd was determined using a graphite furnace atomic absorption spectrophotometer (AA-7000, SHIMADZU, Japan), and As was determined using a dual-channel atomic fluorescence spectrophotometer (AFS-2202E, Beijing Haiguang Instrument, China).

[0039] 4) The expression of transporter proteins in roots, stems and leaves of rice at the jointing and maturity stages was determined by PCR amplification method. The steps are as follows: First, total RNA was extracted, and then cDNA was synthesized according to the steps of the PrimeScript® RT regent Kit With gDNAEraser reverse transcription kit. The sample cDNA obtained by reverse transcription was diluted 10 times, and the internal reference gene was selected. OsActinThe samples were analyzed for expression using the SYBR reagent method. The fluorescent 96-well plate was placed in the ABI 7500 Real-time PCR instrument for amplification. The Cd concentration was determined using an atomic fluorescence spectrometer (AA-7000, SHIMADZU, Japan). As was determined using a dual-channel atomic fluorescence spectrometer (AFS-2202E, Beijing Haiguang Instrument, China). Microsoft Excel2013, OriginLab Origin 2021 and IBMSPSSStatistics 27 were used for data statistical analysis and drawing.

[0040] 4. Results Analysis 1) Effects of adding different soil passivators on the pH of rhizosphere and non-rhizosphere soils at jointing and maturity stages Figure 1 shown.

[0041] Compared with CK, adding soil passivators in different proportions can significantly increase the pH of rhizosphere and non-rhizosphere soils at the jointing stage. Adding 0.5g / 100g BC and 0.5g / 100g SMB to the soil increased the pH of rhizosphere and non-rhizosphere soils by 0.61 units and 0.27 units, respectively; adding 1g / 100g BC and 1g / 100g SMB to the soil increased the pH of rhizosphere and non-rhizosphere soils by 0.69 units and 0.35 units, respectively. Among them, the addition of 1g / 100g SMB had the greatest increase in the pH of rhizosphere and non-rhizosphere soils, increasing by 0.98 units and 0.57 units. Under the same passivator treatment, whether or not to spray foliar silicon fertilizer had no significant effect on the changes in rhizosphere and non-rhizosphere soil pH (P>0.05); the increase in rhizosphere and non-rhizosphere soil pH with the addition of MBC was lower than that with the addition of BC; in addition, compared with the addition of MBC+Si, the addition of SMB had no significant effect on the changes in rhizosphere and non-rhizosphere soil pH (P>0.05).

[0042] Different from the jointing stage, compared with CK, all treatment groups increased the pH of rhizosphere soil in the maturity stage, and the increase of rhizosphere soil pH was greater than that of non-rhizosphere soil. Compared with the treatments of adding BC and MBC, the addition of 1g / 100g SMB to the soil increased the pH of rhizosphere and non-rhizosphere soil by 2.02 and 0.82 units. In general, whether in the jointing stage or the maturity stage, under the same soil passivator treatment, the treatment of spraying foliar silicon fertilizer had no significant effect on the pH of rhizosphere and non-rhizosphere soil (P>0.05), indicating that Si in foliar silicon fertilizer would not affect soil pH; in addition, compared with the treatment of adding MBC+Si, the addition of SMB could slightly increase the pH of rhizosphere and non-rhizosphere soil (P>0.05), that is, CaSiO3 played a certain role in the increase of soil pH. At different growth stages of rice, the change trend of rhizosphere soil pH was more obvious than that of non-rhizosphere soil.

[0043] Overall, compared with CK, different proportions of BC significantly increased the DOC content of rhizosphere and non-rhizosphere soil at the jointing stage (P<0.05), while the addition of different proportions of MBC and SMB reduced the DOC content of rhizosphere and non-rhizosphere soil at the jointing stage to varying degrees. Figure 2 a. Under the same passivation treatment, there was no significant difference in the changes of DOC content in rhizosphere and non-rhizosphere soil between the treatments of foliar silicon fertilizer spraying and the treatments of non-foliar silicon fertilizer spraying (P>0.05); secondly, compared with CK, adding 0.5g / 100g BC to the soil increased the DOC content in rhizosphere and non-rhizosphere soil by 24% and 22%, respectively; adding 1g / 100g BC to the soil increased the DOC content in rhizosphere and non-rhizosphere soil by 44% and 39%, respectively, while adding different proportions of MBC reduced the DOC content in rhizosphere and non-rhizosphere soil, among which the DOC content decreased by 1.7% and 5.2% when 0.5g / 100g MBC was added to the soil, and the DOC content decreased by 13% and 14% when 1g / 100g MBC was added to the soil; in addition, the treatment of adding SMB could reduce the DOC content in rhizosphere and non-rhizosphere soil, but it had no significant effect compared with the treatment of MBC+Si (P>0.05). Effect of adding different passivators on the DOC content in the rhizosphere and non-rhizosphere soil at maturity Figure 2As shown in b. Overall, the changing trend of DOC content in rhizosphere and non-rhizosphere soil during the maturity period was similar to that during the jointing period. Under the same soil passivator treatment, the treatment with foliar silicon fertilizer spraying and the treatment without foliar silicon fertilizer spraying had no significant effect on the changes in DOC content in rhizosphere and non-rhizosphere soil; and compared with CK, the addition of different proportions of BC increased the DOC content in rhizosphere and non-rhizosphere soil, among which the DOC content increased by 28% and 28% after adding 0.5g / 100g BC to the soil, and the DOC content increased by 40% and 43% after adding 1g / 100g BC to the soil, while the addition of different proportions of MBC increased the DOC content in rhizosphere and non-rhizosphere soil. The content of DOC decreased, among which the content of DOC decreased by 2.0% and 7.7% after adding 0.5g / 100g MBC to the soil, and the content of DOC decreased by 8.0% and 13% after adding 1g / 100g MBC to the soil; in addition, compared with the treatment of adding MBC+Si, the addition of SMB had no significant effect on the changes of DOC in rhizosphere and non-rhizosphere soil (P>0.05), indicating that the activity of Si in foliar silicon fertilizer and the activity of Si in CaSiO3 applied to the soil had no significant effect on the changes of soil DOC content. And whether it was at the jointing stage or the maturity stage, the DOC content of non-rhizosphere soil was lower than that of rhizosphere soil.

[0044] 2) Changes in Cd and As concentrations in soil pore water The Cd content in soil pore water under different soil passivators treatments showed a trend of first decreasing, then increasing, and then decreasing with the incubation time. Figure 3 a. Compared with CK, the addition of different passivators reduced the Cd concentration in soil pore water. The addition of SMB reduced Cd in soil pore water by 18% to 53% more than the treatments of adding BC and MBC, respectively. Compared with the treatment of adding BC, the addition of MBC in different proportions reduced Cd in soil pore water by a greater extent.

[0045] From the beginning of cultivation to the 20th day, the addition of different soil passivators can reduce the As concentration in soil pore water. From the 20th day, the As concentration in soil pore water showed an upward trend, reaching the first peak on the 40th day, and then rapidly decreased. The lowest value appeared around the 60th day, and the second peak appeared around the 70th day, and then rapidly decreased until it reached stability on the 80th day. Compared with the blank, the addition of biochar increased the As concentration in soil pore water during the whole growth period of rice, increasing by 0.94%~55%, respectively, while the As concentration in soil pore water decreased in the treatments of magnetic biochar and silicon-rich magnetic biochar, with a decrease of 0.82%~55% and 11%~80%, respectively. Moreover, under the same soil passivator treatment, the more the addition ratio, the greater the reduction of Cd and As in pore water; the treatment with SMB added had a greater reduction in Cd and As in soil pore water than the treatment with MBC+Si, indicating that the addition of sparingly soluble CaSiO3 can achieve the passivation of heavy metals in pore water. The two peaks of As in soil pore water appear at the 40th and 70th days, respectively, corresponding to the tillering and heading stages of rice. During these two stages, the rice roots have a strong absorption effect on water and soil nutrients. The high concentration of nutrients in the soil pore water will cause As to be released from the soil surface into the solution, resulting in two As peaks.

[0046] 3) Changes in soil available Cd and As contents Compared with CK, adding different amounts of soil passivators reduced the available Cd content in rhizosphere and non-rhizosphere soils at the jointing stage to varying degrees, such as Figure 4 a. Under the same soil passivator treatment, the available Cd content in the soil will decrease with the increase of the amount of soil passivator added. Compared with the addition of two soil passivators, BC and MBC, adding 1g / 100g SMB to the soil has the greatest reduction in the available Cd content in the rhizosphere and non-rhizosphere soil, which decreased by 70.4% and 59.4%, respectively. Under the same passivation treatment, the treatment of spraying foliar silicon fertilizer had a certain reducing effect on the content of available Cd in the rhizosphere and non-rhizosphere soil, but there was no significant difference (P>0.05); compared with the treatment of adding BC, the addition of MBC had a greater reduction in the available Cd in the rhizosphere and non-rhizosphere soil. The Cd content of the soil added with 0.5g / 100g MBC decreased by 26% and 24%; the Cd content of the soil added with 1g / 100g MBC decreased by 22% and 20%; in addition, the content of available Cd in the rhizosphere and non-rhizosphere soil in the treatment of adding MBC+Si was higher than that in the treatment of adding SMB, indicating that the insoluble CaSiO3 applied to the soil plays a greater role in reducing the available state of heavy metals in the soil. The content of available Cd in the rhizosphere and non-rhizosphere soil at maturity showed a significant downward trend compared with the blank. Figure 4b in the figure. Compared with the treatments of adding BC and MBC, the addition of 1g / 100g SMB to the soil had the best passivation effect on rhizosphere and non-rhizosphere Cd, reducing 65.5% and 64.7%, respectively. Overall, under the same passivation agent treatment, the treatment of spraying foliar silicon fertilizer had no significant effect on the content of available Cd in the soil at both the jointing stage and the maturity stage (P>0.05); and compared with the treatment of adding MBC+Si, the addition of SMB reduced the content of available Cd in the rhizosphere and non-rhizosphere soil in both periods, but there was no significant difference (P>0.05), and the treatments at the maturity stage had a more significant effect on reducing the available Cd in the rhizosphere and non-rhizosphere soil.

[0047] In the soil at the jointing stage Figure 4 c, compared with the blank control, adding different proportions of BC will increase the content of available As in rhizosphere and non-rhizosphere soil by 1.6%~8.6%, while MBC and SMB can reduce the content of available As in rhizosphere and non-rhizosphere soil, by 36%~38% and 40%~45%, respectively. That is, the content of available As in both rhizosphere and non-rhizosphere soil will increase with the increase of BC addition, and show a downward trend with the increase of SMB and MBC addition. Effects of maturity passivation agents on the content of available As in rhizosphere and non-rhizosphere soils Figure 4 As shown in d, adding different proportions of BC increased the available As content in the soil, while adding different proportions of MBC and SMB could reduce the available As content in the soil. Also, adding 1g / 100g of SMB to the soil had the best effect on reducing the As content in the rhizosphere and non-rhizosphere soil, which was reduced by 33% and 36%, respectively. In general, under the same passivation treatment, the treatment of spraying foliar silicon fertilizer had no significant effect on the available As content in the rhizosphere and non-rhizosphere soil at the jointing and maturity stages (P>0.05); while the treatment of adding BC increased the As content in the rhizosphere and non-rhizosphere soil at the jointing and maturity stages, and the addition of MBC could significantly reduce the available As content in the rhizosphere and non-rhizosphere soil at different growth stages of rice, indicating that iron oxides have a greater effect on reducing the available As content in the soil; among them, compared with the treatment of adding MBC+Si, the addition of SMB slightly reduced the available As content in the soil (P>0.05).

[0048] 4) Rice growth Since rice is in a flooded state for a long time, the oxygen secretion of rice roots makes the rhizosphere environment more reductive. The substances adhere to the surface of rice roots to form an iron film on the root surface, which has the function of adsorbing and intercepting heavy metals. The iron film content under different soil passivation agent treatments is shown in Table 3.

[0049] Table 3 Iron film content on rice root surface at maturity Compared with CK, adding different proportions of passivators can increase the content of iron film on the root surface of rice. Among them, adding 1g / 100g SMB in the soil pond has the largest increase, and the content of iron film on the root surface of rice has increased by 11.8%. Under the same passivator treatment, foliar spraying had no significant effect on the content of iron film on the root surface of rice roots (P<0.05), indicating that foliar silicon fertilizer spraying will not affect the content of iron film on the root surface of rice roots; compared with the treatment of adding BC, the addition of MBC can increase the content of iron film on the root surface of rice roots, which is due to the large amount of iron oxides on the surface of the material; in addition, compared with the treatment of MBC+Si, the addition of SMB can significantly increase the content of iron film on the root surface of rice roots. This is partly due to the presence of iron oxides, and partly due to the application of CaSiO3, the SiO3 in CaSiO3 2- Hydrolysis to form H2SiO3 can oxidize Fe in the soil 2+ Fe 3+ , which easily forms more iron oxides and loads on the surface of rice roots.

[0050] Changes in underground and aboveground biomass of rice Compared with CK, adding different proportions of BC and SMB can promote the growth of Figure 5 a and maturity Figure 5 b. The growth of rice plants in the experiment. The addition of MBC at different ratios inhibited the growth of rice plants. The addition of SMB at different ratios promoted the growth of rice plants more significantly. Figure 5 When 0.5g / 100g was added to the soil pond, the plant height at the jointing stage increased by 21%, and the plant height at the mature stage increased by 18%. When 1g / 100g was added to the soil pond, the plant height at the jointing stage increased by 26%, and the plant height at the mature stage increased by 23%. In addition, the addition of SMB in different proportions will also have a good promoting effect on the aboveground biomass of rice. When 0.5g / 100g was added to the soil pond, the dry weight content at the jointing stage increased by 43%, and the dry weight content at the mature stage increased by 54%. When 1g / 100g was added to the soil pond, the dry weight content at the jointing stage increased by 69%, and the dry weight content at the mature stage increased by 72%. It can be seen that the promoting effect of the addition of soil passivators on rice plants will increase with the increase in the proportion of material added. At the jointing and maturity stages of rice, under the same soil passivator treatment, foliar silicon fertilizer spraying can significantly promote the growth of rice plants at different stages (P<0.05); compared with the treatment of adding BC, adding MBC will reduce the plant height and aboveground dry weight of rice at the jointing and maturity stages, that is, the presence of iron oxides leads to Fe 2+The content increased, further inhibiting the growth of rice plants; the treatments of adding MBC+Si and SMB could significantly increase the plant height and aboveground dry weight of rice plants, indicating that the water-soluble Si in foliar silicon fertilizer and the CaSiO3 on the surface of the material applied to the soil can promote the growth of rice and alleviate iron toxicity. When 1g / 100g SMB was added to the soil, the effect of promoting the plant height and aboveground dry weight of rice was better.

[0051] Changes of Cd and As accumulation in different parts of rice Figure 6 a in the figure shows the changes in the total amount of Cd in various parts of rice plants at the jointing stage. Compared with CK, adding different proportions of passivators can reduce the Cd content in various parts of rice, and under the same passivator treatment, the Cd content in various parts of rice shows a downward trend with the increase of the material addition ratio; the addition of MBC has a greater reduction in the Cd content in various parts of rice than the treatment of adding BC. When the addition amount of MBC in the soil is 0.5g / 100g, the Cd content in the root part is reduced by 25%, the Cd content in the stem part is reduced by 19%, and the Cd content in the leaf part is reduced by 3.1%; when the addition amount of MBC is 1g / 100g, the Cd content in the root part is reduced by 30%, the Cd content in the stem part is reduced by 20%, and the Cd content in the leaf part is reduced by 6.3%; when the addition amount of SMB in the soil is 1g / 100g, the reduction of Cd content is the largest, with a reduction of 67% in the root part, 65% in the stem part, and 82% in the leaf part.

[0052] Different from the trend of total Cd, adding different proportions of BC increased the As content in various parts of rice plants at the jointing stage, while adding different proportions of MBC and SMB decreased the As content in various parts. Figure 6 As shown in b, the largest decrease was observed when 1g / 100g SMB was added to the soil, with the Cd content in the root part reduced by 37%, the Cd content in the stem part reduced by 64%, and the Cd content in the leaf part reduced by 74%. When the amount of material added was the same, the As content in various parts of rice plants would decrease with the application of foliar silicon fertilizer. Under the same passivation treatment, the spraying of foliar silicon fertilizer could reduce the Cd and As content in rice leaves, but had no significant effect on As in rice roots and stems (P>0.05). Compared with the BC treatment, the application of MBC caused a greater reduction in the content of heavy metals (Cd and As) in various parts of rice, indicating that iron oxides play a vital role in reducing the content of heavy metals (Cd and As) in various parts of rice; compared with the treatment of adding MBC+Si, the addition of SMB could significantly reduce the content of Cd and As in various parts of rice (P<0.05), that is, the activity of CaSiO3 in SMB was higher than that of Si in foliar silicon fertilizer. The changes in the total amount of Cd and As in each part of rice at maturity stage were similar to those in rice plants at jointing stage. Figure 6 As shown in c and d in Figure 3. Compared with CK, all treatments can reduce the Cd and As contents in rice grains, among which the largest decrease was observed when 1g / 100g SMB was added to the soil, which decreased by 83.4% and 59.7%, respectively. Different from the changes in Cd and As contents in various parts of rice at the jointing stage, the Cd and As contents in each treatment at the maturity stage were lower than those at the jointing stage.

[0053] Changes in expression of Cd and As transporters in rice Rice parts during jointing stage OsIRT1 , OsNramp1 and OsNramp5 The changes in the expression of Fe and Cd transport proteins Figure 7 Compared with the control, the addition of MBC and SMB can significantly improve the growth rate of rice stems. OsIRT1 Expression; adding different proportions of BC and MBC will OsNramp5 The expression of SMB in various parts of rice plants was up-regulated, while the addition of SMB down-regulated its expression in various parts of rice plants. OsNramp5 It had no significant effect on the expression level in rice roots and stems, but downregulated its expression level in leaves. OsNramp5 The expression levels in different parts of rice are different. Adding BC and SMB will increase the OsNramp1 The expression level in various parts of rice was downregulated, while the addition of MBC had no significant effect. OsNramp1 The expression levels in various parts of rice were also increased, and the decrease rate increased with the increase of the concentration of foliar silicon fertilizer spraying. OsNramp1 The expression level on the leaves was reduced more; however, after applying the material into the soil, OsNramp1 The expression level in the rice root system decreased more. Different from the jointing stage, the addition of different proportions of BC and MBC reduced the expression of various parts of rice plants in the mature stage. OsIRT1 and OsNramp5 The expression of OsNramp5 The expression level in the root was down-regulated, and the down-regulation amount was 19.9% ​​when 0.5g / 100g was added to the soil and 30.3% when 1g / 100g was added to the soil. OsNramp1 The expression levels in various parts of rice were down-regulated, and the largest decrease was observed when 1g / 100g SMB was added to the soil, with a decrease of 43.9% in the root, 63.3% in the stem, and 70.6% in the leaf. Overall, during the jointing and maturity stages of rice, under the same passivation treatment, compared with the treatment without foliar silicon fertilizer spraying, the treatment with foliar silicon fertilizer spraying would reduce the expression of foliar silicon fertilizer to varying degrees. OsNramp1 The expression level of OsNramp1 The expression of transporter proteins was not significantly affected; and compared with the treatment with BC, the addition of MBC increased the expression of various parts of rice plants. OsIRT1 and OsNramp5 The expression levels of Fe and Cd transport proteins were increased by adding SMB. OsNramp1 and OsNramp5 The expression level of the treatment with MBC+Si addition was lower than that in the treatment with MBC+Si addition, indicating that CaSiO3 applied to the soil can inhibit the expression of Fe and Cd transporters in various parts of rice.

[0054] Real-time quantitative PCR analysis OsL , OsLsi2 The expression of As and Si transporters in different parts of rice at jointing and maturity stages. Figure 8 Compared with the blank, adding different proportions of passivation agent can make OsL The expression level in various parts of rice was down-regulated, and the addition of different proportions of passivators would OsLsi2 The expression level in rice roots was down-regulated, but the treatments of spraying foliar silicon fertilizer and adding SMB increased its expression level in rice leaves. When 1g / 100g SMB was added to the soil, OsL , OsLsi2 The expression levels of α, β and β were down-regulated by 50.4%, 58.9%, 77% and 59.2% respectively. Compared with the blank control, the addition of different passivators can down-regulate the expression of various parts of rice at maturity. OsL and OsLsi2 The expression level of BC and BC+Si treatments was different. Figure 8 As shown in c and d, the addition of passivating agent has an effect on OsL , OsLsi2 The inhibitory effect on the expression of various parts of rice will be strengthened with the increase of the proportion of material addition. Adding 0.5g / 100g BC and 1g / 100g BC to the soil can inhibit the expression of rice roots. OsL The increase was 10.9% and 46.5% respectively. Adding different proportions of MBC and SMB would OsL and OsLsi2 The expression level was down-regulated, and when 1g / 100g SMB was added, OsL The adjustment range was the largest, with roots down by 38%, stems down by 60%, and leaves down by 70%. OsLsi2 The largest reduction was 59.4% in the root, 69.5% in the stem, and 74% in the leaf. In general, under the same soil passivator treatment, spraying foliar silicon fertilizer would OsL The expression level in leaves was down-regulated, but in the roots of rice without foliar silicon fertilizer treatment OsL and OsLsi2 There was no significant difference in the expression of OsL and OsLsi2 There was no significant effect on the expression level (P>0.05), but the maturity period was significantly downregulated OsL and OsLsi2 The expression level indicates that different growth stages of rice will have different effects on various aspects of the plant; and whether it is the jointing stage or the maturity stage, compared with the MBC+Si treatment, the addition of SMB can make all parts of rice OsL and OsLsi2 It is worth noting that the treatment of spraying foliar silicon fertilizer and adding SMB significantly improved the jointing period. OsLsi2 The expression level of α-SiO2 in rice leaves (P<0.05) indicated that both soluble Si in foliar silicon fertilizer and insoluble CaSiO3 in SMB had an important effect on the growth of rice leaves at the jointing stage. OsLsi2 had a significant effect on the expression level.

[0055] 5. Overall repair mechanism The addition of SMB could significantly reduce the Cd content in various parts of rice at the jointing and maturity stages, with the Cd and As contents in grains being 0.13 mg·kg -1 and 1.79 mg kg -1 , which are all lower than the national standard value (GB 2762-2017). The restoration of the soil-rice system by the material is mainly achieved through four ways: changing the Cd and As content in pore water, reducing the effectiveness of Cd and As in soil, increasing the iron film content on the root surface of rice roots, and regulating the expression of Cd and As transport proteins.

[0056] 1) The addition of SMB reduced the content of heavy metals Cd and As in soil pore water at the jointing and maturity stages. Heavy metals in pore water are the most active and most easily absorbed and utilized by plants, so the application of SMB can reduce the accumulation of heavy metals in rice grains. SMB can reduce the mobility of Cd in pore water through mechanisms such as electrostatic adsorption and complexation, and the iron oxides and CaSiO3 loaded on its surface can also reduce the content of Cd and As in pore water through adsorption, complexation and co-precipitation.

[0057] 2) The addition of SMB reduces the effectiveness of heavy metals in soil. The effective content of heavy metals in soil reflects the ability of plants to absorb and utilize them, and the addition of SMB reduces the effective Cd and As content in soil by changing the physical and chemical properties and the way the material is adsorbed. First, the addition of materials can not only enhance the absorption of Cd by increasing the soil pH value, but also improve the absorption of Cd by plants. 2+ Electrostatic adsorption can also form hydroxyl oxides with substances in the soil to form Cd 2+Provide more adsorption sites to reduce its mobility in the soil; secondly, the addition of SMB reduces the concentration of soil DOC, and DOC will compete with As for the adsorption sites on the surface of soil particles, so the reduction of its concentration will promote the adsorption of As and Cd by soil particles; in addition, SMB (SiO3 2- ) can form silicon-cadmium complexes (Fe-O-Si-Cd) and Fe-O-As complexes with Cd and As in the soil to adsorb and fix heavy metals Cd and As. This further reduces the mobility of Cd and As in the soil and reduces their entry into rice from the source.

[0058] 3) SMB addition can promote rice growth and increase the formation of iron film on the root surface. On the one hand, the addition of materials can increase the silicon content in the cell wall, enhance the resistance of rice to heavy metals, and alleviate the Fe 2+ On the other hand, the iron film on the root surface can serve as a barrier for soil heavy metals to enter the rice root system, and the application of SMB greatly increases the content of the iron film on the root surface, thus effectively inhibiting the absorption of soil heavy metals by the rice root system and further reducing the accumulation of Cd and As in the rice root system.

[0059] 4) The addition of materials affects the migration and transport of Cd and As in the soil-rice system by regulating the expression of Cd and As transport proteins in rice. The main mechanisms of influence are as follows: the application of SMB increases the migration of Si from the root to the stem of rice during the jointing period, increases the thickness of the cell wall, improves the resistance of rice to Cd, and promotes its growth. The Fe in the soil during the maturity period 3+ It is transported in the plant in chelated form, inhibiting OsIRT1 The expression of SMB in rice can further reduce the absorption and transport of Cd by rice by competing with Cd transporter channels; the addition of SMB can reduce the absorption of Cd by regulating the insoluble CaSiO3 in the material. OsNramp1 and OsNramp5 Participate in the absorption process of heavy metal Cd from rhizosphere solution into cells to inhibit OsNramp1 Expression reduced the transport of Cd between the soil-rice system and rice tissues; by inhibiting the jointing stage OsL and maturity OsL , OsLsi2 The expression level of As in rice was reduced by competing with the transport channel protein during the jointing stage to reduce the transport and accumulation of As in rice.

[0060] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A silicon-iron modified biochar for reducing the absorption of cadmium and arsenic by rice, characterized in that: The silicon-iron modified biochar is obtained by mixing and pyrolyzing magnetic biochar and silicate; the magnetic biochar is obtained by mixing magnetite suspension and plant straw; The silicon-iron modified biochar is used to oxidize Fe in soil 2+ , forming an iron film on the surface of rice roots to reduce the absorption of cadmium and arsenic by rice; The mass of the silicate accounts for 0.5% to 1% of the mass of the magnetic biochar.

2. The silicon-iron modified biochar according to claim 1, characterized in that: The silicate is CaSiO3.

3. The silicon-iron modified biochar according to claim 1, characterized in that: The particle size of the silicon-iron modified biomass charcoal is 1 μm to 100 μm.

4. The silicon-iron modified biochar according to claim 1, characterized in that: The pyrolysis temperature is 700° C. to 720° C., and the insulation time is 2 h to 2.5 h.

5. The silicon-iron modified biochar according to claim 4, characterized in that: The pyrolysis is carried out in an inert gas atmosphere.

6. The silicon-iron modified biochar according to claim 5, characterized in that: The inert gas is nitrogen.

7. The silicon-iron modified biochar according to claim 1, characterized in that: The specific process of obtaining the magnetic biochar is as follows: The plant straw and the magnetite suspension are mixed in a mass volume ratio of 20 kg: 400 L to 410 L, the pH is adjusted to 11 to 12, the mixture is reacted at 60° C. to 65° C. for 2 h to 2.5 h, the mixture is allowed to stand, and the mixture is filtered to obtain the magnetically modified biochar; The magnetite suspension is obtained by mixing FeSO4 and FeCl3 in a molar ratio of 1:1.8-2 and causing a coprecipitation reaction in water.

8. A use of the silicon-iron modified biochar according to any one of claims 1 to 7 in the preparation of a soil passivator.

9. The use according to claim 8, characterized in that: The soil passivator is used for adjusting the pH value of rhizosphere soil, reducing the concentration of Cd and As in soil pore water, and reducing the content of effective Cd and As in soil.

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