Preparation method of carbon-based nano-enzyme and application of carbon-based nano-enzyme in promoting salt tolerance and nutrient absorption of plants

Abstract

The invention provides an application of a carbon-based nano enzyme in promoting salt tolerance and nutrient absorption of plants. The invention also provides a preparation method of the carbon-based nano enzyme, which comprises the following steps: dissolving the amino-containing compound and the carboxyl-containing organic acid in ultrapure water, and performing ultrasonic treatment to form a precursor solution; performing hydrothermal reaction on the precursor solution to obtain a reaction product; and carrying out pH value adjustment, microporous filtration, dialysis purification and freeze drying on the reaction product to obtain the carbon-based nano enzyme. The prepared carbon-based nano-enzyme is prepared into an aqueous solution, the aqueous solution is applied to a saline-alkali soil environment with the salt content of 0.60-0.80% through foliar spraying, the salt tolerance of crops such as cotton, rice and wheat can be effectively promoted, and growth and nutrient absorption of the crops are promoted. The preparation method is simple and convenient in process and good in environmental compatibility, and a novel nano material technical scheme is provided for saline water agriculture.

Description

Technical Field

[0001] This invention belongs to the field of agricultural nanomaterials technology, specifically relating to a method for preparing carbon-based nanoenzymes and their application in promoting plant salt tolerance and nutrient absorption. Background Technology

[0002] Globally, saline soils are widespread, especially in arid and semi-arid regions, where high salinity poses a persistent threat to ecosystem stability and agricultural production. High salinity causes multiple stresses on plant growth: firstly, excessive salt content in the soil increases osmotic potential, hindering the absorption of water and nutrients by plant roots and triggering physiological drought; secondly, excessive salt ions, such as sodium ions, have toxic effects on cell membrane structure, enzyme activity, and metabolic balance, while also inducing a large accumulation of reactive oxygen species, causing oxidative damage. More importantly, salt stress significantly inhibits the absorption and translocation of essential nutrients such as nitrogen, phosphorus, and potassium, leading to nutrient imbalance, decreased photosynthetic capacity, and ultimately, stunted growth and reduced yield.

[0003] Currently, agricultural technologies used to alleviate salt stress mainly fall into three categories: first, screening and planting salt-tolerant crop varieties; second, applying organic or inorganic soil conditioners to reduce the toxic effects of salt ions; and third, using precision irrigation methods such as drip irrigation under mulch to inhibit salt accumulation in the topsoil. However, these methods all have certain limitations: breeding salt-tolerant varieties is time-consuming and resource-intensive, their resistance is significantly constrained by genetic background, and their regional adaptability is generally poor; while soil conditioners can improve the root zone environment in the short term, their effects are difficult to sustain, are easily lost due to water migration, and long-term use may cause soil structure damage and environmental pollution; while precision irrigation technology can reduce external salt input, it cannot systematically improve the salt tolerance of plants from the perspective of their internal physiological mechanisms, making it difficult to ensure stable crop yields under high salinity conditions. Therefore, the existing technological system still lacks a regulatory strategy for alleviating crop salt stress that can actively stimulate the salt tolerance physiological functions of crops and has both ecological safety and field applicability.

[0004] To address the aforementioned technical bottlenecks, a new class of zero-dimensional carbon-based nanozymes shows unique application prospects. Carbon-based nanozymes possess advantages such as wide availability of raw materials, excellent water solubility, and high biocompatibility. They can be absorbed by plants through foliar spraying or root application, thereby systematically regulating the physiological response of crops to salt stress. Existing research indicates that carbon-based nanozymes can participate in multiple metabolic pathways, not only enhancing leaf photosynthetic performance and promoting the synthesis and transport of dry matter such as carbohydrates, but also effectively scavenging reactive oxygen species (ROS), reducing oxidative damage, and maintaining the stability of cell membrane structure and function, thus comprehensively improving crop salt tolerance. Compared with traditional methods, this material treatment has advantages such as rapid response, good environmental compatibility, and no harmful residues.

[0005] Nevertheless, existing research on carbon-based nanozymes still has significant shortcomings in agricultural applications: most studies focus on the promoting effects of nanomaterials on crops under normal growth conditions, while carbon-based nanozymes and their supporting application technologies developed for the specific adversity scenario of salt stress are still relatively lacking; at the same time, existing research does not clarify the mechanism of action of such materials in regulating key physiological processes under salt stress (such as the regulation of ion homeostasis and osmotic balance), and the material design lacks specificity; in addition, there are no systematic reports on comprehensive technical solutions that can simultaneously achieve the triple goals of "salt damage mitigation - growth enhancement - yield increase" for saline-alkali soil environments.

[0006] Therefore, there is an urgent need to develop a novel carbon-based nanoenzyme and its supporting application methods that is suitable for saline-alkali soil environments, can effectively enhance crop salt tolerance through multi-pathway synergistic mechanisms, significantly promote plant growth, and achieve breakthroughs in yield. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing carbon-based nanozymes and their application in promoting salt tolerance and nutrient absorption in plants, which addresses the shortcomings of the prior art. The carbon-based nanozymes prepared by the present invention can effectively promote the salt tolerance of crops such as cotton, corn, rice, wheat and jujube trees, and promote their growth and nutrient absorption.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: the application of a carbon-based nanoenzyme in promoting plant salt tolerance and nutrient absorption.

[0009] Preferably, the carbon-based nanoenzyme is used for crop cultivation in saline-alkali soil environments. The application method is as follows: dissolve the carbon-based nanoenzyme in water to prepare a carbon-based nanoenzyme aqueous solution, and spray the carbon-based nanoenzyme aqueous solution onto the leaves of the crop.

[0010] Preferably, the crops include cotton, rice, and wheat; the salinity of the saline-alkali soil is 0.60-0.80%; the concentration of the carbon-based nanoenzyme aqueous solution is 50 μg / ml, 150 μg / ml, or 200 μg / ml, and the spraying rate is 30-50 L per acre.

[0011] This invention also provides a method for preparing carbon-based nanozymes, the method comprising the following steps:

[0012] S1. Preparation of precursor solution: Add amino-containing compounds and carboxyl-containing organic acids to ultrapure water and sonicate until a homogeneous and clear precursor solution is formed.

[0013] S2, hydrothermal reaction: The precursor solution obtained in S1 is transferred to a reaction vessel and hydrothermal reaction is carried out under sealed conditions. After the hydrothermal reaction is completed, it is cooled to room temperature to obtain the reaction product.

[0014] S3. Purification and Collection: Adjust the pH value of the reaction product obtained in S2, then filter it, purify it by dialysis, and finally freeze-dry it to obtain carbon-based nanozymes.

[0015] Preferably, the amino-containing compound in S1 is urea, chitosan, ethylenediamine, or polyethyleneimine; the carboxyl-containing organic acid is citric acid, ascorbic acid, or glutathione; and the mass-volume ratio of the amino-containing compound, the carboxyl-containing organic acid, and ultrapure water is 1 g: (4-6) g: 30 ml.

[0016] Preferably, the hydrothermal reaction in S2 is carried out at a temperature of 180-200 °C for 5-8 h.

[0017] Preferably, in step S3, the pH of the reaction product is adjusted to 6.5-7.0 using an acidic solution and an alkaline solution. The acidic solution is hydrochloric acid with a mass fraction of 3.00-15.00%, and the alkaline solution is a solution with a molar concentration of 0.20-1.00 mol∙L⁻¹. -1 The process involves using a sodium hydroxide solution; filtration is performed using a microporous membrane with a pore size of 0.22 μm; dialysis is performed using a dialysis bag with a molecular weight cutoff of 500-1000 Da, and the dialysis time is 24-72 h; the freeze-drying temperature is -60 ℃, and the time is 24-72 h.

[0018] The present invention also provides a carbon-based nanozyme, which is prepared by the above-described method for preparing a carbon-based nanozyme.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The carbon-based nanozyme preparation process provided by this invention is simple, the raw materials are inexpensive and readily available, the reaction conditions are mild and easy to control, the entire process does not require complex equipment, the product quality is stable, it is suitable for large-scale preparation, and has extremely high potential for industrial application.

[0021] 2. The carbon-based nanozyme in this invention has good environmental friendliness and biosafety. It can be naturally degraded in the environment without the risk of secondary pollution, which meets the requirements of green agriculture and sustainable development.

[0022] 3. This invention avoids the adverse effects of high-salt environments in the root zone on material activity. Carbon-based nanozymes are directly and rapidly absorbed through leaf stomata or epidermis. Once inside the plant, they quickly activate the antioxidant system, scavenging excess reactive oxygen species induced by salt stress and mitigating membrane lipid peroxidation damage. Simultaneously, they synergistically improve leaf photosynthetic performance by enhancing light energy conversion efficiency, electron transport, and Rubisco enzyme activity. Not only is the action pathway direct and the response rapid, but it is also environmentally friendly and does not easily disturb the rhizosphere microecology.

[0023] 4. The application method provided by this invention is flexible and low-cost. The application concentration and timing can be flexibly adjusted according to the specific salinity level in the field, providing an efficient, economical and easy-to-promote yield-increasing solution for crops with different degrees of salinization.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a comparison chart of cotton yield in Example 1 when sprayed with carbon-based nanoenzyme aqueous solution and when not sprayed with carbon-based nanoenzyme aqueous solution.

[0026] Figure 2 This is a comparison chart of malondialdehyde content in cotton treated with and without carbon-based nanoenzyme aqueous solution in Example 1.

[0027] Figure 3 This is a comparison of Rubisco enzyme activity in cotton treated with and without carbon-based nanoenzyme aqueous solution in Example 1.

[0028] Figure 4 This is a comparison chart of cotton plant height in Example 2 after spraying with carbon-based nanoenzyme aqueous solution and before spraying with carbon-based nanoenzyme aqueous solution.

[0029] Figure 5 This is a comparison chart of nitrogen content in cotton under different conditions (e.g., sprayed with carbon-based nanoenzyme aqueous solution and unsprayed with carbon-based nanoenzyme aqueous solution) in Example 2.

[0030] Figure 6 This is a comparison chart of the dry matter weight of cotton in Example 3 after spraying with carbon-based nanoenzyme aqueous solution and before spraying with carbon-based nanoenzyme aqueous solution.

[0031] Figure 7 This is a comparison chart of phosphorus content in cotton treated with and without carbon-based nanoenzyme aqueous solution in Example 3.

[0032] Figure 8 This is a TEM image of the carbon-based nanozyme prepared in Example 1.

[0033] Figure 9This is a comparison of CAT enzyme activity in rice after spraying with carbon-based nanoenzyme aqueous solution and before spraying with carbon-based nanoenzyme aqueous solution in Example 2.

[0034] Figure 10 This is a comparison chart of the biomass of rice in Example 2 after spraying with carbon-based nanoenzyme aqueous solution and before spraying with carbon-based nanoenzyme aqueous solution.

[0035] Figure 11 This is a comparison of Rubisco enzyme activity in rice after spraying with a carbon-based nanoenzyme aqueous solution and before spraying with a carbon-based nanoenzyme aqueous solution in Example 2.

[0036] Figure 12 This is a comparison chart of wheat biomass under different conditions: one after spraying with carbon-based nanoenzyme aqueous solution and the other without spraying with carbon-based nanoenzyme aqueous solution, as shown in Example 3.

[0037] Figure 13 This is a comparison chart of POD enzyme activity in wheat treated with and without carbon-based nanoenzyme aqueous solution in Example 3.

[0038] Figure 14 This is a comparison diagram of photosystem II of wheat in Example 3, with and without the application of carbon-based nanoenzyme aqueous solution. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment provides a method for preparing carbon-based nanozymes, which includes the following steps:

[0042] S1. Preparation of precursor solution: Add 1 g of urea and 4 g of citric acid to 30 ml of ultrapure water and sonicate until a homogeneous and clear precursor solution is formed.

[0043] S2, hydrothermal reaction: The precursor solution obtained in S1 is transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed and placed in an oven. The hydrothermal reaction is carried out at 180 °C for 5 h. After the hydrothermal reaction is completed, the reactor is allowed to cool naturally to room temperature (25 °C) to obtain the reaction product.

[0044] S3. Purification and Collection: Use 3.00% hydrochloric acid and 0.20 mol∙L⁻¹ hydrochloric acid.-1 The pH of the reaction product obtained in S2 was adjusted to 6.5 with sodium hydroxide solution. Then, large particulate impurities were removed by filtration through a microporous membrane with a pore size of 0.22 μm. After purification, the product was purified by dialysis through a dialysis bag with a cutoff diameter of 500 Da for 24 h. Finally, the product was freeze-dried at a temperature of -60 ℃ for 24 h to obtain solid carbon-based nanozyme powder.

[0045] Application and comparative experiments were conducted:

[0046] like Figure 1 As shown, foliar spraying of the "Xinluzao 61" cotton variety was conducted in the experimental field during the boll-forming stage. The carbon-based nanoenzyme powder prepared in this embodiment was dissolved in water to prepare three concentrations of carbon-based nanoenzyme aqueous solutions: 50 μg / ml, 150 μg / ml, and 200 μg / ml. An equal volume of water was used as a control. The application rate was 40 L per acre, and the soil salinity was maintained at 0.60%. All treatment groups grew under these conditions. During the boll-opening stage, representative samples were selected from each treatment plot, and all opened cotton bolls were manually harvested. After drying, the seed cotton weight was measured and converted into yield per unit area. All treatment groups showed significant yield increases. Measurement data showed that compared with the control group, the cotton yield of the three concentration treatment groups increased by 53.95%, 50.71%, and 42.44%, respectively. This result confirms that foliar spraying of carbon-based nanoenzymes at appropriate concentrations can effectively promote cotton yield under saline-alkali soil conditions. Simultaneously, after spraying a carbon-based nanoenzyme aqueous solution with a concentration of 50 μg / mL, Figure 2 The malondialdehyde (MDA) content in the cotton leaves shown was significantly lower than that in the control group by 47.2%, indicating that spraying carbon-based nanoenzyme aqueous solution can effectively remove reactive oxygen species and reduce membrane lipid peroxidation damage. Figure 3 The Rubisco enzyme activity in the leaves shown was 44.4% higher than that in the control group, confirming its significant enhancement of photosynthetic carbon assimilation capacity. At harvest, 15 representative plants from each plot were selected, and their height was measured from the base of the stem to the top using a steel tape measure. Figure 4 As shown, the plant height of the three concentration treatment groups increased by 14%, 7% and 4%, respectively, demonstrating a significant concentration-dependent growth-promoting effect. Figure 5As shown, after spraying with a 50 μg / mL carbon-based nanozyme aqueous solution, the total nitrogen content of cotton plants increased by approximately 33.3% compared to the control group. This synergistic improvement in the above physiological indicators explains, mechanistically, how carbon-based nanozymes promote crop growth and yield formation under salt stress by reducing oxidative stress and improving light energy utilization efficiency. Furthermore, the selected plants were divided into three parts: roots, stems, and leaves. The samples were then dried in an oven to constant weight, and the dry weight of each organ was measured to analyze the dry matter accumulation of cotton plants. All treatment groups showed good promoting effects. Compared to the control group, the dry matter content of roots, stems, and leaves in the 50 μg / mL treatment group increased significantly by 56.87%, 39.62%, and 53.35%, respectively (Figure 6), and the total phosphorus content increased by approximately 35% (Figure 6). Figure 7 As shown in the figure, it exhibits optimal biomass accumulation. This result indicates that carbon-based nanozymes not only enhance the absorption and assimilation of key nutrients such as nitrogen and phosphorus by plants, but also provide a more sufficient material and energy basis for growth and metabolism under salt stress conditions.

[0047] like Figure 8 As shown, a high-resolution transmission electron microscope image of the carbon-based nanozyme prepared in this embodiment shows that the carbon-based nanozyme has a distinct lattice structure. Through analysis of about 100 particles, the lattice spacing of the carbon-based nanozyme was measured to be about 0.31 nm.

[0048] Example 2

[0049] This embodiment provides a method for preparing carbon-based nanozymes, which includes the following steps:

[0050] S1. Preparation of precursor solution: Add 1 g chitosan and 5 g ascorbic acid to 30 ml of ultrapure water and sonicate until a homogeneous and clear precursor solution is formed.

[0051] S2, hydrothermal reaction: The precursor solution obtained in S1 was transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed and placed in an oven. The hydrothermal reaction was carried out at 190 °C for 6 h. After the hydrothermal reaction was completed, the reactor was allowed to cool naturally to room temperature (25 °C) to obtain the reaction product.

[0052] S3. Purification and Collection: Use 10.00% hydrochloric acid or 0.50 mol∙L⁻¹ hydrochloric acid. -1 The pH of the reaction product obtained in S2 was adjusted to 6.7 with sodium hydroxide solution. Then, large particulate impurities were removed by filtration through a microporous membrane with a pore size of 0.22 μm. After purification, the product was purified by dialyzing through a dialysis bag with an 800 Da cutoff diameter for 36 h. Finally, the product was freeze-dried at -60 ℃ for 50 h to obtain solid carbon-based nanozyme powder.

[0053] Application and comparative experiments were conducted:

[0054] At the experimental base, foliar spraying was applied to the "Jindao 112" variety during the tillering stage. The carbon-based nanoenzyme powder prepared in this embodiment was dissolved in water to prepare three concentrations of carbon-based nanoenzyme aqueous solutions: 50 μg / ml, 150 μg / ml, and 200 μg / ml. An equal volume of water was used as a control. The application rate was 50 L per acre, and the soil salinity was maintained at a uniform 0.70%. All treatment groups grew under these conditions. Regarding the antioxidant system, such as... Figure 9 As shown, spraying with a 50 μg / mL carbon-based nanoenzyme aqueous solution increased the activity of catalase (CAT) in rice leaves by approximately 25.7%, effectively enhancing the plant's endogenous antioxidant enzyme system, accelerating H2O2 scavenging, and alleviating salt stress-induced oxidative damage. Regarding plant biomass accumulation, the 50 μg / mL treatment group significantly promoted the accumulation of substances in various organs. Figure 10 The increased biomass in roots, stems, and leaves indicates that carbon-based nanozymes can systematically promote the overall growth and structural development of crops under salt stress. Regarding the activity of key photosynthetic enzymes, such as... Figure 11 As shown, the Rubisco enzyme activity in the 50 μg / mL treatment group increased by approximately 22.4%, further confirming that carbon-based nanozymes can significantly enhance photosynthetic carbon assimilation efficiency, providing more abundant photosynthetic products for plant growth under salt stress. The systematic enhancement of CAT activity, biomass, and Rubisco enzyme activity demonstrates that foliar spraying with an appropriate concentration of carbon-based nanozyme aqueous solution can effectively promote the vegetative growth of rice under saline-alkali soil conditions.

[0055] Example 3

[0056] This embodiment provides a method for preparing carbon-based nanozymes, which includes the following steps:

[0057] S1. Preparation of precursor solution: Add 1 g of ethylenediamine and 6 g of glutathione to 30 ml of ultrapure water and sonicate until a homogeneous and clear precursor solution is formed.

[0058] S2, hydrothermal reaction: The precursor solution obtained in S1 is transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed and placed in an oven. The hydrothermal reaction is carried out at 200 °C for 8 h. After the hydrothermal reaction is completed, the reactor is allowed to cool naturally to room temperature (25 °C) to obtain the reaction product.

[0059] S3. Purification and Collection: Use 15.00% hydrochloric acid or 1.00 mol∙L⁻¹ hydrochloric acid. -1The pH of the reaction product obtained in S2 was adjusted to 7.0 with sodium hydroxide solution. After removing large particulate impurities by filtration through a microporous membrane with a pore size of 0.22 μm, the product was purified by dialysis through a dialysis bag with a cutoff diameter of 1000 Da for 72 h. Finally, the product was freeze-dried at a temperature of -60 ℃ for 72 h to obtain solid carbon-based nanozyme powder.

[0060] In this embodiment, the amino-containing compound in S1 can also be polyethyleneimine; the hydrothermal reaction temperature in S2 can also be 182℃, 193℃, 184℃, 185℃, 186℃, 187℃, 188℃, 189℃, 191℃, 192℃, 193℃, 194℃, 195℃, 196℃, 197℃, 198℃, or 199℃, and the reaction time can also be 5.5 h, 5.7 h, 5.8 h, 5.9 h, 6.2 h, 6.5 h, 6.7 h, 6.8 h, 6.9 h, 7.0 h, 7.2 h, 7.4 h, 7.5 h, 7.7 h, 7.8 h, or 7.9 h; the pH value of the reaction product in S3 can also be 6.6, 6.7, 6.8, or 6.9; and the mass fraction of hydrochloric acid can also be 4.00. %, 5%, 6%, 8%, 9%, 11%, 12%, 13% or 45.00%; the molar concentration of sodium hydroxide solution can also be 0.30 mol∙L. -1 0.40 mol∙L -1 0.60 mol∙L -1 0.70 mol∙L -1 0.80 mol∙L -1 Or 0.90 mol∙L -1 The molecular weight cutoff of the dialysis bag can also be 600 Da, 700 Da, 900 Da or 950 Da; the dialysis time can also be 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, 55 h, 60 h or 65 h; the freeze-drying time can also be 25 h, 30 h, 35 h, 40 h, 45 h, 50 h, 55 h, 60 h or 65 h.

[0061] Application and comparative experiments were conducted:

[0062] At the experimental base, one-year-old "Zhengmai 379" wheat plants were treated with foliar spraying during the jointing stage. The carbon-based nanozyme powder prepared in this embodiment was dissolved in water to prepare three concentrations of carbon-based nanozyme aqueous solutions: 50 μg / ml, 150 μg / ml, and 200 μg / ml. An equal volume of water was used as a control. The application rate was 30 L per acre, and the soil salinity was maintained at 0.80%. All treatment groups grew under these conditions. At harvest, 10 representative plants from each plot were selected and divided into root, stem, and leaf sections. The samples were then dried in an oven to constant weight, and the dry weight of each organ was measured for analysis of wheat plant dry matter accumulation (e.g., ...). Figure 12 (As shown). Regarding overall plant growth, carbon-based nanozyme treatment significantly promoted the accumulation of total biomass. The 50 μg / mL treatment group increased the total biomass by approximately 14.4%, further confirming the overall growth-promoting effect of simultaneous increase in dry matter in all organs (roots, stems, and leaves). This result indicates that carbon-based nanozymes provide a more sufficient material and energy basis for growth and metabolism under salt stress. Meanwhile, as... Figure 13 The peroxidase (POD) activity increased by approximately 74.6%. This indicates that carbon-based nanozymes can synergistically activate multiple endogenous antioxidant enzymes, systematically enhancing reactive oxygen species scavenging capacity, thereby effectively alleviating salt stress-induced oxidative damage. The Fv / Fm value of PSII increased by approximately 34.8% (e.g., Figure 14 (As shown in the figure), indicating that carbon-based nanozymes can not only enhance light energy capture and conversion efficiency, but also simultaneously promote the activity of key carbon assimilation enzymes, thereby comprehensively improving the photosynthetic performance of leaves under salt stress.

[0063] The above results, including synergistic enhancement of POD activity, improved photosynthetic performance (PSII), and significant accumulation of biomass in various organs, indicate that carbon-based nanozymes effectively alleviate salt stress inhibition and comprehensively enhance the physiological adaptability and yield potential of crops in saline-alkali environments.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. Application of a carbon-based nanozyme in promoting salt tolerance and nutrient absorption in plants.

2. The application of the carbon-based nanoenzyme according to claim 1 in promoting plant salt tolerance and nutrient absorption, characterized in that, The carbon-based nanoenzyme is used for crop cultivation in saline-alkali soil environments. The application method is as follows: dissolve the carbon-based nanoenzyme in water to prepare a carbon-based nanoenzyme aqueous solution, and spray the carbon-based nanoenzyme aqueous solution onto the leaves of the crop.

3. The application of the carbon-based nanoenzyme according to claim 2 in promoting plant salt tolerance and nutrient absorption, characterized in that, The crops include cotton, rice, and wheat; the salinity of the saline-alkali soil is 0.60-0.80%; the concentration of the carbon-based nanoenzyme aqueous solution is 50 μg / ml, 150 μg / ml, or 200 μg / ml, and the application rate is 30-50 L per acre.

4. A method for preparing carbon-based nanozymes, characterized in that, The preparation method includes the following steps: S1. Preparation of precursor solution: Add amino-containing compounds and carboxyl-containing organic acids to ultrapure water and sonicate until a homogeneous and clear precursor solution is formed. S2, hydrothermal reaction: The precursor solution obtained in S1 is transferred to a reaction vessel and hydrothermal reaction is carried out under sealed conditions. After the hydrothermal reaction is completed, it is cooled to room temperature to obtain the reaction product. S3. Purification and Collection: Adjust the pH value of the reaction product obtained in S2, then filter it, purify it by dialysis, and finally freeze-dry it to obtain carbon-based nanozymes.

5. The method for preparing a carbon-based nanozyme according to claim 4, characterized in that, The amino-containing compound in S1 is urea, chitosan, ethylenediamine or polyethyleneimine; the carboxyl-containing organic acid is citric acid, ascorbic acid or glutathione; the mass-volume ratio of the amino-containing compound, the carboxyl-containing organic acid and the ultrapure water is 1 g: (4-6) g: 30 ml.

6. The method for preparing a carbon-based nanozyme according to claim 4, characterized in that, The hydrothermal reaction described in S2 is carried out at a temperature of 180-200 ℃ for 5-8 h.

7. The method for preparing a carbon-based nanozyme according to claim 4, characterized in that, In step S3, the pH of the reaction product is adjusted to 6.5-7.0 using acidic and alkaline solutions. The acidic solution is hydrochloric acid with a mass fraction of 3.00-15.00%, and the alkaline solution is a solution with a molar concentration of 0.20-1.00 mol∙L⁻¹. -1 The process involves using a sodium hydroxide solution; filtration is performed using a microporous membrane with a pore size of 0.22 μm; dialysis is performed using a dialysis bag with a molecular weight cutoff of 500-1000 Da, and the dialysis time is 24-72 h; the freeze-drying temperature is -60 ℃, and the time is 24-72 h.

8. A carbon-based nanozyme, characterized in that, It is prepared by the method for preparing a carbon-based nanozyme according to any one of claims 4-7.

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