Tomato straw carbon dots as well as preparation method and application thereof

Abstract

The invention provides tomato straw carbon dots as well as a preparation method and application thereof, and belongs to the field of nano technologies and nano materials. The method comprises the following steps: crushing tomato straws, adding water according to a mass ratio of 1: (90-110), carrying out ultrasonic treatment, and heating at 130-200 DEG C for 6-10 hours; after centrifugation, filtration and dialysis, freeze drying is performed, and the tomato straw carbon dots are prepared. The tomato straw carbon dots are used as a root promoting agent or a plant growth auxiliary agent, the germination potential, the germination rate and the number of radicles and lateral roots of muskmelon seeds can be effectively increased, the root system of muskmelon seedlings is promoted to be more robust, and the plant growth vigor is more vigorous. In a saline-alkali soil environment, the tomato straw carbon dot aqueous solution can also be used for treating melon seeds to obtain a good effect, melon root systems can reach the growth level in non-saline-alkali soil, and the effect is remarkable.

Description

Technical Field

[0001] The invention belongs to the field of nanotechnology and nanomaterials, and specifically relates to a tomato straw carbon dot and a preparation method and application thereof. Background Art

[0002] During the summer harvest and autumn and winter every year, a large amount of straw is piled up in the farmland. Burning straw in rural areas can cause environmental pollution, easily cause fires, damage the soil and waste land resources. The straw of solanaceous vegetables such as tomatoes, eggplants, and peppers is different from the straw of ordinary grain crops. It has an inhibitory effect on the growth of the next crop of vegetables, so it cannot be directly returned to the field. At the same time, if the amount of returned to the field is too large or the tillage is uneven, it is easy to cause a conflict between soil microorganisms and crop seedlings for nutrients, and even yellow seedlings, dead seedlings, and reduced production. The comprehensive development and utilization of straw is faced with the dilemma of immature technology, large investment, and poor results.

[0003] Carbon quantum dots (CQDs), also known as carbon dots (CDs), as a new type of fluorescent nanomaterial, exhibit many excellent properties, such as photostability, good biocompatibility, hydrophilicity and easy surface modification. They have been widely used in agriculture, bioimaging, biosensing, fluorescent labeling and optoelectronic devices.

[0004] my country is the country with the largest tomato planting area and the highest yield in the world. By 2022, the planting area and yield will reach 1.1692 million hectares and 69.7077 million tons respectively, resulting in a large amount of accumulation and idleness of tomato straw, which has caused a series of environmental problems. The harmless treatment and resource utilization of tomato straw have become one of the pain points of horticultural production (Zhang Feixue et al., 2023). However, there is no research on the use of tomato straw as a carbon source in the preparation of carbon quantum dots using biomass carbon sources.

[0005] The melon root system has the characteristic of early development, but the regeneration ability of the melon root system is weak. Generally, it is difficult to recover after the roots are damaged. If the seedlings are transplanted, they should be transplanted as early as possible to avoid root damage. The melon root system is prone to corking. The older the seedlings are, the deeper the corking is, and it is difficult to root. It is difficult to recover after the roots are damaged. If the roots are damaged before pollination, the roots can slowly recover after the stress is lifted; but if the roots are damaged after pollination, it is difficult for the plant to recover, and continuous wilting and withering will occur. Therefore, once there is a problem with the melon root system, it will directly affect the healthy growth of the melon. At present, there are relatively few studies on melon root problems, and there are few products or methods to solve related problems. Summary of the invention

[0006] The purpose of the present application is to overcome at least one of the deficiencies of the prior art. To this end, in a first aspect of the present application, a tomato straw carbon dot and a preparation method thereof are provided.

[0007] The second aspect of the present application provides the application of tomato straw carbon dots in promoting the growth of plant roots, especially the growth of plant roots in saline-alkali land environments.

[0008] The third aspect of the present application provides a melon root promoter and a plant growth promoter in a saline-alkali land environment.

[0009] The fourth aspect of the present application provides a method for growing melon seedlings and a method for growing plants in a saline-alkali land environment.

[0010] The technical solution adopted in this application is:

[0011] A method for preparing tomato straw carbon dots (TS-CDs: Tomato Straw Carbon Dots) comprises the following steps:

[0012] (1) Crush tomato straw;

[0013] (2) Weigh tomato straw powder, add water in a mass ratio of 1:(90-110), and continue ultrasonic treatment for 25-35 minutes; transfer the suspension to a reactor and heat at 130-200°C for 6-10 hours;

[0014] (3) centrifuging the obtained mixture at 3000 r / min-8000 r / min for 15-35 min; after centrifugation, collecting the supernatant and filtering it to obtain a liquid product;

[0015] (4) dialyzing the obtained liquid product;

[0016] (5) The dialysis solution is freeze-dried to prepare tomato straw carbon dots.

[0017] In some embodiments, in step (2), heating is performed at 160-180° C. for 8-9 h.

[0018] In some of the embodiments, in step (3), the obtained mixture is centrifuged at 4000-5000 r / min for 20-30 min.

[0019] The rotation speed and time during centrifugation are to separate the quantum dot solution and the reactant residue, thereby speeding up the filtration process and preventing the residue from clogging the filter paper to the greatest extent.

[0020] In some of the embodiments, the filtration in step (3) is vacuum filtration, and the pore size of the filter membrane used in the vacuum filtration is 0.22 μm-0.6 μm.

[0021] The purpose of filtration is to remove the residues that are not completely reacted during the reaction.

[0022] In some of the embodiments, the dialysis bag used for dialysis in step (4) has a molecular weight cutoff of 3500 μm.

[0023] A tomato straw carbon dot, wherein the raw material for preparing the tomato straw carbon dot is tomato straw.

[0024] In some of the embodiments, the raw material for preparing the tomato straw carbon dots is tomato straw, which is obtained by the above-mentioned preparation method.

[0025] Application of tomato straw carbon dots in promoting root growth of plants, including melon.

[0026] Application of tomato straw carbon dots in promoting root growth of plants in saline-alkali soil environments, wherein the plants include melons.

[0027] A melon root promoter, wherein the active ingredient of the root promoter is tomato straw carbon dots, and the concentration is not higher than 200 μg ml -1 .

[0028] A plant growth aid in saline-alkali land environment, wherein the active ingredient of the plant growth aid is tomato straw carbon dots, and the concentration is not higher than 200 μg ml -1 The main function of the adjuvant is to promote root growth. The root growth includes but is not limited to root growth during seed germination, promoting root regrowth of plants after root cutting after transplantation, and / or root growth of plants after transplantation.

[0029] A method for growing melon seedlings, comprising soaking seeds and accelerating germination, wherein the concentration used in the soaking and germination process is 50-200 μg·ml -1 Melon seeds were treated with tomato straw carbon dots aqueous solution.

[0030] In some embodiments, seeds are dried in the sun before soaking and germination. For example, 2 to 3 days before sowing, melon seeds are placed in a sunny place for 1 to 2 days to increase the vitality of the melon seeds.

[0031] A method for planting plants in a saline-alkali land environment comprises the following steps: during the planting process of the plants, the plant seeds are treated with a tomato straw carbon dot aqueous solution and then transplanted to the saline-alkali land, and / or, the plant seedlings are treated with a tomato straw carbon dot aqueous solution and then transplanted to the saline-alkali land, and / or, after planting the plant seeds or plants in the saline-alkali land, the tomato straw carbon dot aqueous solution is used for watering.

[0032] The beneficial effects of this application are:

[0033] The present application utilizes discarded tomato straw to prepare tomato straw carbon dots (TS-CDs) by a hydrothermal method, thereby utilizing the discarded straw, reducing the accumulation of discarded straw, and avoiding environmental pollution caused by incineration.

[0034] The tomato straw carbon dots of the present application can effectively promote the root growth of melons. Experiments have shown that using a tomato straw carbon dot aqueous solution to treat melon seeds during the seed soaking and germination process can effectively improve the germination potential, germination rate, and number of radicles and lateral roots of melon seeds. When raising seedlings in plug trays, continuing to spray the tomato straw carbon dot aqueous solution can promote a stronger root system for the melon seedlings and a more vigorous growth of the plants.

[0035] In a saline-alkali land environment, good results can be achieved by treating melon seeds with the tomato straw carbon dot aqueous solution of the present application. The melon root system can reach the growth level in non-saline-alkali land, and the effect is significant. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the hydrothermal synthesis process of CDs.

[0037] Figure 2 Characterization of carbon dots prepared using tomato straw as the carbon source, where A is the TEM image of TS-CDs and B is the particle size distribution diagram.

[0038] Figure 3 : Fluorescence emission spectra of carbon dots at different excitation wavelengths.

[0039] Figure 4 UV-visible absorption spectrum of TS-CDs.

[0040] Figure 5 is the Fourier transform infrared spectrum of TS-CDs.

[0041] Figure 6 X-ray diffraction of TS-CDs.

[0042] Figure 7 X-ray photoelectron spectrum of TS-CDs.

[0043] Figure 8 For the cytotoxicity experiment, the viability of African green monkey kidney epithelial cells treated with different concentrations of TS-CDs.

[0044] Fig. 9 The phenotypes of adventitious root regeneration in melon at different time periods.

[0045] Fig.10 The changes in the root primordium of melon adventitious root regeneration in different time periods (the white arrow in the figure points to the protrusion of the root primordium).

[0046] Fig.11was water and 150 μg ml -1 Related indices of root regeneration from melon adventitious roots after TS-CDs treatment.

[0047] Among them, (A) is the root length of melon adventitious root regeneration induced by TS-CDs on different days; (B) is the root surface area of ​​melon adventitious root regeneration induced by TS-CDs on different days; (C) is the root projection area of ​​melon adventitious root regeneration induced by TS-CDs on different days; (D) is the root volume of melon adventitious root regeneration induced by TS-CDs on different days; (E) is the average root diameter of melon adventitious root regeneration induced by TS-CDs on different days; (F) is the total number of root tips of melon adventitious root regeneration induced by TS-CDs on different days; (G) is the number of branches of melon adventitious root regeneration induced by TS-CDs on different days; (H) is the number of intersections of melon adventitious root regeneration induced by TS-CDs on different days.

[0048] Fig.12 Longitudinal paraffin sections of melon seedling stems with different treatments.

[0049] Fig.13 The phenotypes of adventitious root regeneration in melon after being treated with water and different concentrations of TS-CDs for 7 days.

[0050] Fig.14 Figure 2 is the fluorescence emission spectra of carbon dots at different reaction temperatures at the same excitation wavelength.

[0051] Fig.15 Figure 2 is the fluorescence emission spectra of carbon dots at different reaction times at the same excitation wavelength.

[0052] Fig.16 The phenotypes of carbon dots in adventitious root regeneration of melon at different reaction temperatures.

[0053] Fig.17 The phenotypes of carbon dots in adventitious root regeneration of melon under different reaction times.

[0054] Fig.18 The phenotype of TS-CDs on adventitious root regeneration in tomato.

[0055] Fig.19 TS-CDs promote melon seed germination phenotype.

[0056] Fig. 20 TS-CDs alleviate the salt tolerance phenotype of melon seeds.

[0057] Fig.21 Spray 150 μg ml after the cotyledons are flattened -1 The carbon dots solution can promote the growth phenotype of melon seedlings.

[0058] Fig. 22150 μg ml for irrigation after planting -1 The carbon dot solution can promote the survival phenotype. DETAILED DESCRIPTION

[0059] The experimental methods in the following examples of the present invention, where no specific conditions are specified, are usually carried out under conventional conditions or under conditions recommended by the manufacturers. The various commonly used chemical reagents used in the examples are all commercially available products.

[0060] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0061] The terms "including" and "having" and any variations thereof of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, device, product or equipment comprising a series of steps is not limited to the listed steps or modules, but may optionally include steps not listed, or may optionally include other steps inherent to these processes, methods, products or equipment.

[0062] In the present invention, the term "multiple" refers to two or more than two. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0063] This application uses a hydrothermal method to synthesize tomato straw CDs. The process diagram is shown in Figure 1 .

[0064] A method for preparing tomato straw carbon dots (TS-CDs: Tomato Straw Carbon Dots) comprises the following steps:

[0065] (1) Crush tomato straw;

[0066] (2) Weigh tomato straw powder, add water in a mass ratio of 1:(90-110), and continue ultrasonic treatment for 25-35 minutes; transfer the suspension to a reactor and heat at 130-200°C for 6-10 hours;

[0067] (3) centrifuging the obtained mixture at 3000 r / min-8000 r / min for 15-35 min; after centrifugation, collecting the supernatant and filtering it to obtain a liquid product;

[0068] (4) dialyzing the obtained liquid product;

[0069] (5) The dialysis solution is freeze-dried to prepare tomato straw carbon dots.

[0070] In the process of preparing straw carbon dots, the role of ultrasound is mainly reflected in the following aspects: accelerating the dispersion and peeling of materials, improving the surface activity of materials, promoting physical reactions, improving the uniformity of materials, etc.

[0071] In some embodiments, in step (2), the ultrasonic power is 150W and the frequency is 40kHz. The ultrasonic device used in the technical solution of this application is a laboratory ultrasonic device, and those skilled in the art can adjust the parameters of the ultrasonic device according to actual conditions.

[0072] In some embodiments, in step (2), heating is performed at 160-180° C. for 8-9 h.

[0073] In some of the embodiments, in step (3), the obtained mixture is centrifuged at 4000-5000 r / min for 20-30 min.

[0074] The rotation speed and time during centrifugation are to separate the quantum dot solution and the reactant residue, thereby speeding up the filtration process and preventing the residue from clogging the filter paper to the greatest extent.

[0075] In some of the embodiments, the filtration in step (3) is vacuum filtration, and the pore size of the filter membrane used in the vacuum filtration is 0.22 μm-0.6 μm.

[0076] The purpose of filtration is to remove the residues that are not completely reacted during the reaction.

[0077] In some of the embodiments, the dialysis bag used for dialysis in step (4) has a molecular weight cutoff of 3500 μm.

[0078] The purpose of dialysis is to retain the desired macromolecules and remove extremely small molecules.

[0079] In some embodiments, the freeze drying in step (5) is achieved by using a freeze dryer.

[0080] A tomato straw carbon dot, wherein the raw material for preparing the tomato straw carbon dot is tomato straw.

[0081] In some of the embodiments, the raw material for preparing the tomato straw carbon dots is tomato straw, which is obtained by the above-mentioned preparation method.

[0082] Application of tomato straw carbon dots in promoting root growth of plants, including melon.

[0083] A melon root promoter, wherein the active ingredient of the root promoter is tomato straw carbon dots, and the concentration is not higher than 200 μg ml -1 .

[0084] A method for growing melon seedlings, comprising soaking seeds and accelerating germination, wherein the concentration used in the soaking and germination process is 50-200 μg·ml -1 Melon seeds were treated with tomato straw carbon dots aqueous solution.

[0085] In some embodiments, seeds are dried in the sun before soaking and germination. For example, 2 to 3 days before sowing, melon seeds are placed in a sunny place for 1 to 2 days to increase the vitality of the melon seeds.

[0086] Seed drying is to spread the selected seeds evenly on clean paper or straw mats and choose a clear, windless and sunny day to dry them. Turn the seeds every 2 hours to allow them to be evenly exposed to sunlight. Drying the seeds can promote seed ripening, enhance seed vitality, and improve seed germination potential and germination rate. At the same time, the ultraviolet rays and high temperatures in the sun can kill some pathogens carried on the seeds and reduce the occurrence of diseases transmitted through seeds. Moreover, the drier the seeds are, the faster they absorb water when soaked later, which is conducive to seed germination.

[0087] A method for planting plants in a saline-alkali land environment comprises the following steps: during the planting process of the plants, the plant seeds are treated with a tomato straw carbon dot aqueous solution and then transplanted to the saline-alkali land, and / or, the plant seedlings are treated with a tomato straw carbon dot aqueous solution and then transplanted to the saline-alkali land, and / or, after planting the plant seeds or plants in the saline-alkali land, the tomato straw carbon dot aqueous solution is used for watering.

[0088] The following is a description of the specific examples. The melon seeds used in the following examples and comparative examples are all of the "Yangjiaomi" variety.

[0089] The tomato straw used in the embodiments of the present application refers to the dried product of the whole tomato plant (including stems and leaves) obtained after the tomato fruit is harvested and air-dried or baked. During the air-drying or baking of the whole plant and the subsequent transportation process, the leaves are easy to fall off, so the tomato straw is mainly composed of the stems, with a small amount of leaves retained.

[0090] Example 1: Preparation of tomato straw carbon dots

[0091] (1) Wash and dry the tomato stalks, then crush them into powder using a grinder and sieve them.

[0092] (2) Weigh 3 g of tomato straw powder and 300 mL of double distilled water into a beaker (1:100), and treat with ultrasound (power 150 W, frequency 40 kHz) for 30 min. Transfer the suspension into a 500 mL polyvinyl fluoride reactor, heat at 200 °C for 6 h, and wait for the reactor to cool to room temperature.

[0093] (3) The resulting mixture was centrifuged at 8000 r / min for 15 min. After centrifugation, the supernatant was collected and filtered under reduced pressure using a 0.22 μm filter membrane to obtain an orange-yellow liquid product.

[0094] (4) The obtained product was transferred into a dialysis bag with a molecular weight cutoff of 3500 μm, placed in a large beaker filled with deionized water, and dialyzed for 3 days, changing the water every 24 hours until the liquid was basically colorless.

[0095] (5) The solution in the dialysis bag is tomato straw carbon dots (TS-CDs). After freezing, it is placed in a freeze dryer and freeze-dried into carbon dot powder, which is then collected and stored at 4°C for later use.

[0096] Example 2: Preparation of tomato straw carbon dots

[0097] (1) Wash and dry the tomato stalks, then crush them into powder using a grinder and sieve them.

[0098] (2) Weigh 3 g of tomato straw powder and 300 mL of double distilled water into a beaker (1:100), and treat with ultrasound (power 150 W, frequency 40 kHz) for 30 min. Transfer the suspension into a 500 mL polyvinyl fluoride reactor, heat at 180 ° C for 8 h, and wait for the reactor to cool to room temperature.

[0099] (3) The resulting mixture was centrifuged at 4000 r / min for 20 min. After centrifugation, the supernatant was collected and filtered under reduced pressure using a 0.22 μm filter membrane to obtain an orange-yellow liquid product.

[0100] (4) The obtained product was transferred into a dialysis bag with a molecular weight cutoff of 3500 μm, placed in a large beaker filled with deionized water, and dialyzed for 3 days, changing the water every 24 hours until the liquid was basically colorless.

[0101] (5) The solution in the dialysis bag is tomato straw carbon dots (TS-CDs). After freezing, it is placed in a freeze dryer and freeze-dried into carbon dot powder, which is then collected and stored at 4°C for later use.

[0102] Test Example 1

[0103] The tomato straw carbon dots prepared in Example 2 were characterized.

[0104] In the characterization of carbon dots, (1) TEM is used to observe the structure, size and dispersity of carbon quantum dots and determine whether their particle size range meets the requirements of the composite nanometer level. (2) Fluorescence emission spectra under different excitation wavelengths are used to observe the luminescence characteristics of carbon quantum dots under different excitation wavelengths and determine the optical properties of the prepared carbon dots. (3) UV-visible absorption spectra can provide information on the electronic structure of nanoparticles. In the measurement of the biological effects of nanomaterials, the UV-visible absorption of nanoparticles will cause signal interference in the biological effect experiment. (4) In the Fourier transform infrared spectroscopy experiment, because the vibration of different chemical bonds of carbon dots has a specific absorption frequency in the infrared region, the structure of carbon quantum dots can be determined by observing the position and intensity of each peak in the spectrum image. (5) In the identification of material states, different material states have different diffraction effects on X-rays, so X-ray diffraction spectra (XRD) can be used to distinguish between crystalline and amorphous states. Generally, the XRD spectrum of amorphous materials is a straight line. The XRD of diffuse peaks that appear at low 2θ angles that we usually encounter is generally composed of liquid solids and gas solids. (6) X-ray photoelectron spectroscopy (XPS) can confirm the presence of hydrophilic groups on the surface of carbon quantum dots, proving that they have good water solubility.

[0105] In the following characterization experiments, the transmission electron microscope images of CDs were completed using a transmission electron microscope (TEM). The fluorescence (Photoluminescence, PL) spectrum was measured using a fluorescence spectrophotometer. The ultraviolet-visible (Ultraviolet-visible, UV-Vis) absorption spectrum was measured using an ultraviolet-visible absorption spectrometer. The Fourier transform infrared (Fourier transforminfrared spectrometer, FT-IR) spectrum was measured using a Fourier transform infrared spectrometer. The X-ray photoelectron spectrum (X-ray photoelectron spectrum, XPS) and diffraction (X-ray diffratometer, XRD) were measured by an electron spectrometer and an X-ray diffractometer, respectively.

[0106] Results Figure 2-Figure 7 .

[0107] Figure 2 Characterization of carbon dots prepared using tomato straw as the carbon source, where A is the TEM image of TS-CDs and B is the particle size distribution diagram. Figure 3 : Fluorescence emission spectra of carbon dots at different excitation wavelengths. Figure 4 UV-visible absorption spectrum of TS-CDs. Figure 5 is the Fourier transform infrared spectrum of TS-CDs. Figure 6 is the X-ray diffraction spectrum of TS-CDs. Figure 7 X-ray photoelectron spectrum of TS-CDs.

[0108] like Figure 2 As shown in A, it can be seen with the naked eye that the carbon dots prepared using tomato straw as the carbon source in the present application are approximately spherical in shape, uniform in size, well dispersed, and have no agglomeration phenomenon. Figure 2 B is the particle size distribution diagram after TEM image analysis. Figure 2 B shows that the average diameter of TS-CDs is 2.17 nm, which meets the particle size requirements of nanomaterial carbon dots.

[0109] Figure 3 A is the fluorescence emission spectra of tomato straw carbon dots at different excitation wavelengths. The TS-CDs (Tomato straw carbon dots) prepared in Example 2 were irradiated with excitation light of 300, 325, 350, 375, 400, 425, 450, 475, 500, and 525 nm, respectively. It can be seen that the fluorescence intensity is the highest when irradiated with the excitation light of 350 nm ( Figure 3 A). Then, the TS-CDs were irradiated with an excitation light of 350 nm. It can be seen that the peak of the emitted light is around 455 nm. The wavelength range of blue light is 450-480 nm. Therefore, it can be proved that the TS-CDs prepared in Example 2 are carbon dots that emit blue fluorescence, and the fluorescence intensity emitted is the strongest when irradiated with an excitation light of 350 nm ( Figure 3 B). This indicates that the prepared tomato straw carbon dots have good optical properties.

[0110] from Figure 4 It can be seen from the UV-visible absorption spectrum of TS-CDs that in the ultraviolet wavelength range of 200-800nm, the absorbance of TS-CDs gradually decreases with the increase of the excitation wavelength, and it has a strong absorption capacity in the ultraviolet region of 200-470nm ( Figure 4 ); at the same time, a strong absorption peak is shown at 286nm, which is attributed to the transition of the chromophore. The absorption peak at 286nm in the UV-visible spectrum can be attributed to the π→π* transition of electrons in the conjugated system of the carbon core, indicating that Ts-CDs have excellent luminescence ability. The emission characteristics of Ts-CDs can be attributed to the energy characteristics of down-conversion, indicating its optoelectronic properties.

[0111] The surface functional groups of TS-CDs were detected by Fourier transform infrared spectroscopy, such as Figure 5 As shown, 3421cm -1 and 1649cm -1The stretching vibration regions of OH and C=O are 1103cm -1 The stretching vibrations of CO and CN and the single bond skeleton vibration of CC are shown in Figure 2. This indicates that the synthesized tomato straw carbon dots have various organic functional groups, which can improve the hydrophilicity and stability of carbon dots in aqueous systems and promote the further functionalization and application of carbon dots.

[0112] exist Figure 6 In the X-ray diffraction spectrum of TS-CDs, the characteristic peaks of carbon dots usually appear in the 2θ angle range of 20-30°. Among them, the strongest peak is usually around 25°. Figure 6 As shown in the figure, a very broad diffraction package appears near the peak at about 25°, which proves that the prepared carbon dots are amorphous structures ( Figure 6 ).

[0113] Figure 7 X-ray photoelectron spectrum of TS-CDs. It can be seen from the full spectrum that the TS-CDs prepared in Example 2 contain three elements: C, N and O. TS-CDs contain three peaks, located at 284.03, 398.95 and 532.26 eV, corresponding to C1s (71.6%), N1s (23.36%) and O1s (5.04%), respectively. The N1s spectrum can fit a peak of 398.98 eV, which belongs to CN. The two peaks of O1s are located at 531.68 and 532.82 eV, which belong to OH and CO, respectively. The C1s spectrum illustrates the existence of CC / C=C (283.99 eV), CN (285.19 eV), C=O (287.88 eV) and OCO (285.96 eV). The above FTIR and XPS spectra both show that the surface of the TS-CDs of the present application is rich in hydrophilic groups (-OH and -COOH), which is consistent with the excellent water dispersibility.

[0114] Test Example 2

[0115] In order to ensure the biological safety of TS-CDs, African green monkey kidney epithelial cells were treated with TS-CDs prepared in Example 2 at different concentrations to conduct cytotoxicity experiments, and the cell survival rate 3 days after treatment was calculated.

[0116] Cytotoxicity test method: African green monkey kidney epithelial cells (Marc-145) in good growth state were transferred to 96-well plates and inoculated into each well with about 1×10 4cells, and the same sample was repeated 3 times. The culture plate was placed in a constant temperature incubator and incubated for 24 hours. After discarding the culture medium and washing with phosphate buffered saline (PBS), 200 μL of CDs culture medium dilutions of different concentrations were added to each well, with water as a control, and incubated for 24 hours. Then 10 μL CCK-8 solution (CCK-8 kit) was added to each well. After adding the reagent, the culture plate was gently shaken to help mix. Then it was returned to the incubator and incubated for 2 hours. The OD value at 450nm was measured using a microplate reader to calculate the cell viability. The experiment was set up with three independent biological replicates.

[0117] Results Figure 8 , Figure 8 The results showed that when the concentration of TS-CDs was no more than 150 μg·mL -1 Under the condition of , the cell survival rate was stable at more than 95%, and there was no obvious toxic side effect. However, when the concentration was higher than 150 μg·mL -1 The cell survival rate decreased gradually with the increase of TS-CDs concentration. -1 When the concentration of tomato straw carbon dots is less than 200 ng / ml, the cell survival rate drops to 67%, which is 33% lower than the control, showing a certain degree of cytotoxicity. In summary, the tomato straw carbon dots of the present application can promote growth at a concentration of no more than 200 ng / ml.

[0118] Example 3: Application of tomato straw carbon dots prepared in Example 2 as root promoter in melon growth

[0119] After germination, the seeds of the melon variety 'Yangjiaomi' were selected and sown. When the cotyledons of the seedlings were flattened, the seedlings with the same growth were selected for root cutting (root cutting was performed at the junction of the green and white stems with a sharp blade). After root cutting, the seedlings were fixed in a centrifuge tube with a sponge. The centrifuge tube contained 150 μg mL -1 The TS-CDs aqueous solution (prepared in Example 2) and water were used as two treatments, and three replicates were set for each.

[0120] Determination of root indexes of melon adventitious root regeneration induced by TS-CDs: On the third day, the seedlings were placed in a root scanner to take pictures and analyze the relevant root indexes. After that, the analysis was carried out every day until the seventh day when the treatment was completed. The root indexes were measured by a root scanner.

[0121] Determination of the changes in the number of root primordia and cytology of melon adventitious root regeneration induced by TS-CDs: Use the same treatment method as above, gently wipe the solution on the roots of the seedlings with paper after treatment, put them under a stereo microscope to take pictures and observe, put the seedlings back into the centrifuge tubes to continue culturing, take pictures and observe once a day until the roots of both treatments grow on the fourth day. In order to ensure the uniformity of the experiment, the same seedling was observed every day. The changes in the root primordia were measured by stereo microscope; paraffin sections were measured by Wuhan Saiweier Biology.

[0122] Fig. 9 was water and 150 μg ml -1 Phenotype of melon adventitious root regeneration after TS-CDs treatment. Fig. 9 The results showed that on the third day, no roots grew in either treatment group; on the fourth day, only the 150 μg·ml -1 The melon seedlings treated with TS-CDs took root; after the fifth day, both treatment groups grew roots. As time went by, the regenerated root system of melon adventitious roots became longer. In the same period of time, from the fourth to the seventh day, after 150 μg ml -1 The roots of the TS-CDs-treated plants were longer and denser than those of the control group, indicating that TS-CDs can promote the regeneration of adventitious roots of melon earlier.

[0123] Among them, water treatment is similar to rooting by cuttings, and the adventitious roots of melons grown by it are weak, small in number, and thin, which is not conducive to later growth. The melon seedlings treated with tomato straw carbon dots are superior to water treatment in terms of root strength and number. At the same time, carbon dot treatment can improve the photosynthesis of plants and is conducive to the accumulation of organic matter.

[0124] Depend on Fig.10 It can be seen that the hypocotyls that were just cut off had no adventitious root primordia. On the first day, no obvious root primordia were observed in the melon adventitious roots treated with water and TS-CDs. On the second day, it can be seen that the melon adventitious roots treated with TS-CDs had a root primordium, while the control group had no root primordium. On the third and fourth days, it can be clearly seen that the root primordia regenerated by the melon adventitious roots treated with TS-CDs were denser than those treated with the water control group. This shows that TS-CDs can promote the generation of root primordia of melon adventitious root regeneration, and the number of root primordia is denser than that of the control group.

[0125] Fig.11 was water and 150 μg ml -1 Related indices of regenerated root system of melon adventitious roots after TS-CDs treatment. Fig.11 A shows that in the same period of time, after 150 μg ml -1The length of melon adventitious roots regenerated by TS-CDs treatment was significantly higher than that of water control group ( Fig.11 A); from the third to the seventh day, after 150 μg ml -1 The surface area of ​​regenerated roots of melon adventitious roots treated with TS-CDs was significantly higher than that of the water control group ( Fig.11 B); in the same period of time, after 150 μg ml -1 The projected root area of ​​melon adventitious roots regenerated by TS-CDs treatment was significantly higher than that of the control group ( Fig.11 C); From the third to the seventh day, after 150 μg ml -1 The volume of regenerated root system of melon adventitious roots treated with TS-CDs was significantly higher than that of the control group ( Fig.11 D); treated for the same period of time, after 150 μg ml -1 The average diameter of regenerated roots of melon adventitious roots treated with TS-CDs was significantly higher than that of the control group ( Fig.11 E); treated for the same period of time, after 150 μg ml -1 The number of regenerated root branches of melon adventitious roots treated with TS-CDs was significantly higher than that of the control group ( Fig.11 F); from the same number of days, after 150μg·ml -1 The total number of root tips regenerated from adventitious roots of melon treated with TS-CDs was significantly higher than that of the control group ( Fig.11 G); in the same period of time, after 150 μg ml -1 The number of root crossings of melon adventitious roots regenerated by TS-CDs treatment was significantly higher than that of the control group ( Fig.11 H). This indicates that TS-CDs can promote the growth of melon roots earlier.

[0126] Fig.12 This is a longitudinal paraffin section of the stem of a melon seedling. It can be seen that 24 hours after treatment, the seedlings treated with TS-CDs produced protrusions of root primordia from the vascular bundle, while the control group did not have protrusions of root primordia in the same period; 60 hours after treatment, the control group had only one protrusion of root primordia, while the TS-CDs-treated seedlings had three protrusions of root primordia, which was significantly more than the control group; 72 hours (3 days) after treatment, a large number of root primordia protruded from the vascular bundle in the control group, and the root primordia treated with TS-CDs in the same period had already broken out of the epidermis to form adventitious roots.

[0127] Screening experiment of TS-CDs growth-promoting concentration: After the cotyledons of melon seedlings were flattened, the roots were cut off and the seedlings after root cutting were placed in 0 μg·mL -1 , 100 μg·mL -1 , 150μg·mL-1 and 200 μg mL -1 After 7 days of treatment with TS-CDs aqueous solution, 9 seedlings were randomly selected for phenotypic observation to evaluate the phenotype of adventitious root regeneration in melon.

[0128] Depend on Fig.13 It can be seen that the adventitious root regeneration of melon treated with TS-CDs was longer and more numerous than that treated with water. 150μg·mL -1 The regeneration root system of melon adventitious roots treated with TS-CDs was higher than that of 100 μg·mL -1 The results of the TS-CDs treatment were significantly better and more consistent. This indicates that with the increase of TS-CDs concentration, the regeneration of melon adventitious roots grew better until the concentration increased to 200 μg·mL -1 When the concentration was less than 150 μg·mL, the effect of TS-CDs on adventitious root regeneration of melon was smaller. -1 There is concentration dependence; when the concentration is 150μg·mL -1 When the concentration of TS-CDs was more than 150 μg·mL, the effect of TS-CDs on adventitious root regeneration of melon was the most significant and uniform. -1 When the concentration is less than 10 μg / mL, the positive effect of promoting adventitious root regeneration is weakened. Therefore, the effective concentration is finally determined as 150 μg / mL -1 optimal.

[0129] The relevant data are shown in Table 1:

[0130] Table 1

[0131]

[0132]

[0133] Example 4: Preparation of tomato straw carbon dots and application of tomato straw carbon dots in promoting adventitious root growth of melon seedlings

[0134] The temperature and time of the reaction in the reactor in step (2) were adjusted to explore the effects of the reaction temperature and reaction time on the tomato straw carbon dots. The other steps were the same as in Example 2.

[0135] The specific steps are as follows:

[0136] (1) Wash and dry the tomato stalks, then crush them into powder using a grinder and sieve them.

[0137] (2) Weigh 3 g of tomato straw powder and 300 mL of double distilled water into a beaker (1:100) and treat with ultrasound for 30 min. Transfer the suspension into a 500 mL polyvinyl fluoride reactor and react at 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C for 8 h or at 180°C for 6 h, 7 h, 8 h, 9 h, 10 h, and wait for the reactor to cool to room temperature.

[0138] (3) The resulting mixture was centrifuged at 4000 r / min for 20 min. After centrifugation, the supernatant was collected and filtered under reduced pressure using a 0.22 μm filter membrane to obtain an orange-yellow liquid product.

[0139] (4) The obtained product was transferred into a dialysis bag with a molecular weight cutoff of 3500 μm, placed in a large beaker filled with deionized water, and dialyzed for 3 days, changing the water every 24 hours until the liquid was basically colorless.

[0140] (5) The carbon dot powder was obtained by freeze-drying in a freezer and stored at 4°C.

[0141] The fluorescence emission spectra of carbon quantum dots prepared at different reaction temperatures were observed at an excitation wavelength of 450nm. It can be seen from the spectrum that the fluorescence signal is strongest when the reaction temperature is 180℃ ( Fig.14 ); At the same time, the fluorescence emission spectra of the carbon quantum dots prepared at different reaction times were observed at an excitation wavelength of 450nm. From the spectrum, it can be seen that the fluorescence signal is strongest when the reaction temperature is 8h ( Fig.15 ). In order to further verify the effect of different reaction temperatures and reaction times on the promotion of adventitious roots in melon seedlings, the inventors conducted rooting experiments at different preparation times and temperatures. The experimental results confirmed the fluorescence emission spectrum results at an excitation wavelength of 450nm. The experimental results proved that the growth of adventitious roots at a reaction temperature of 180°C and a reaction time of 8h was better than that at other times and temperatures ( Fig.16 , Fig.17 ).in Fig.14 and Fig.16 Corresponding to the step (2), tomato straw carbon dots were prepared by reacting at 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 200°C for 8h, wherein Fig.15 and Fig.17 Correspondingly, in step (2), tomato straw carbon dots were prepared by reacting at 180° C. for 6 h, 7 h, 8 h, 9 h, and 10 h.

[0142] It can be seen that the reaction time and reaction temperature in step (2) of the technical solution of the present application are crucial. Too high a temperature or too long a time will lead to serious carbonization of the quantum dots produced, resulting in a decrease in their quality.

[0143] Example 5: Application of the tomato straw carbon dots prepared in Example 2 as a root promoter in tomato growth

[0144] In order to further prove that the root promoter can be applied to other crops, the tomato straw carbon dots were tested in tomato seedlings. The results showed that 150 μg ml -1 On the third day after the tomato seedlings were treated with TS-CDs, the control group had no roots, while the TS-CDs-treated group had adventitious roots. On the fourth day, both groups had adventitious roots. However, after 150 μg ml -1 The adventitious roots of tomato seedlings treated with TS-CDs were superior to those of the control group, proving that 150 μg ml -1 TS-CDs treatment of tomato seedlings can significantly promote the production of adventitious roots ( Fig.18 ).

[0145] Example 6: Use of the tomato straw carbon dots prepared in Example 2 as a root promoter

[0146] Select the melon "Yangjiaomi" seeds with full grains and place them in the prepared carbon dot solution (50, 100, 150 μg ml -1 ) and 0 μg ml -1 As a control (equivalent to water treatment), the seeds were soaked for 10 hours, and then spread on the soaked filter paper (the carbon dot solution or water used for soaking was the same as that used for soaking seeds), and placed in a dark incubator at 28°C for germination. During this process, the filter paper was kept moist to allow normal growth. Three plants were randomly selected for observation and index determination under different concentrations.

[0147] 16 hours after treatment, it was found that the germination potential of the seeds treated with carbon dots was better than that of the control, and the germination rate was better than that of the control at 72 hours. After 72 hours, the growth of the seeds treated with carbon dots was observed to be better than that of the control water treatment, and the number of lateral roots in the carbon dot treatment group was better than that of the control group. In addition, the melon seedlings treated with carbon dots grew uniformly and were generally better than those in the control treatment. Therefore, soaking seeds with carbon dot solution can effectively improve the germination potential, germination rate, and number of radicles and lateral roots of melon seeds ( Fig.19 ).

[0148] Specifically, at 16 h, 50, 100, and 150 μg ml compared with CK -1 The germination potential of carbon dots treatment increased by 27.58%, 35.30%, and -4.77% respectively; at 72h, compared with CK, 50, 100, and 150 μg·ml -1 The germination rates of carbon dots treatment increased by 15.62%, 11.47%, and 12.90%, respectively; at 72h, compared with CK, 50, 100, and 150 μg·ml-1 The number of lateral roots treated with carbon dots increased by 22.90%, 31.00%, and 29.95%, respectively; at 72h, compared with CK, 50, 100, and 150 μg·ml -1 The epicotyls treated with carbon dots increased by 20.69%, 19.76%, and 29.19% respectively; at 72h, compared with CK, 50, 100, and 150 μg·ml -1 The hypocotyls treated with carbon dots increased by 6.91%, 22.43% and 14.42% respectively.

[0149] In conventional melon planting, direct seeding is the main method. This method cannot ensure the uniformity of germination to a certain extent. The radicle grown after direct seeding is weak and the number of lateral roots is small, which is not conducive to growth and later seedbed management. Workers are required to screen and remove poor seedlings and deformed seedlings, which undoubtedly increases production costs. For this problem, the technical solution of this application can effectively solve the problems of germination rate and germination potential, avoid problems such as deformed seedlings caused by poor root growth of melons, reduce the screening process of workers, and greatly reduce production costs.

[0150] Example 7: Use of tomato straw carbon dots in saline-alkali land

[0151] In order to further explore whether carbon dots can alleviate the salt tolerance of melon seeds, the inventors selected full melon seeds and soaked them in 60°C water for disinfection. -1 TS-CDs, 150mM NaCl+100μg·ml -1 TS-CDs, 150mM NaCl+150μg·ml -1 For TS-CDs treatment, seeds were soaked for 10 h, spread on a culture dish covered with two layers of filter paper, an equal amount of water was added to the filter paper, and the seeds were cultured in an incubator in the dark and observed in time.

[0152] The water treatment group simulated the growth of melon seeds in a normal environment, the 150 mM NaCl treatment group simulated the growth of melon seeds in a saline-alkali environment, and the 150 mM NaCl + 50 μg ml -1 TS-CDs, 150mM NaCl+100μg·ml -1 TS-CDs, 150mM NaCl+150μg·ml -1 The TS-CDs treatment group simulated the growth of melon seeds in a saline-alkali environment, so as to investigate the effects of different concentrations of carbon dot solutions on the growth of melon seeds under salt stress.

[0153] At 16 h after treatment, the germination rates of the water treatment group (CK) and the 150 mM NaCl group were 41.66% and 21.66%, respectively; 150 mM NaCl + 50 μg ml -1 TS-CDs, 150mM NaCl+100μg·ml -1 TS-CDs, 150mM NaCl+150μg·ml - 1 The germination rates of TS-CDs were 30%, 40%, and 30%, respectively. That is, at 16 hours, under saline-alkali conditions, the melon seeds treated with TS-CDs could recover to the level under normal conditions.

[0154] Results Fig. 20 The phenotype is the melon root system after 72 hours of culture. The analysis of the melon root system after 7 days of culture showed that compared with the control group, the melon root system treated with 150mM / L NaCl was significantly weaker than that of the control group and had fewer lateral roots. The epicotyls grew delicately. The 150mM / L NaCl treatment affected the normal growth of the melon hypocotyls. -1 TS-CDs, 150mM NaCl+100μg·ml -1 TS-CDs, 150mM NaCl+150μg·ml -1 TS-CDs were simultaneously soaked in 150 mM NaCl and 100 μg ml -1 and 150 μg ml -1 When treated with carbon dot solution, the growth of melon root system (hypocotyl) returned to normal level (the level of water treatment group), and after 150mM NaCl + 150μg ml -1 The epicotyls treated with TS-CDs were slightly stronger than those in the control (water treatment group) but there was no significant difference. At the same time, the ratio of lateral roots and epicotyls treated with 150mM NaCl+TS-CDs returned to the normal level of the control (water treatment group), proving that the salt tolerance of seeds treated with carbon dots increased and the damage caused by salt stress could be effectively alleviated ( Fig. 20 ).

[0155] Saline-alkali land refers to land with high salt content in the soil, which affects the normal growth of vegetation. Generally speaking, the salt content classification standards of saline-alkali land are as follows: the salt content of mild saline-alkali land is 0.1-0.2%, the salt content of moderate saline-alkali land is 0.2-0.4%, and the salt content of severe saline-alkali land is 0.4-0.6%.

[0156] That is, there is about 0.1g of sodium chloride in 100g of soil in light saline-alkali land, and 150mM / L NaCl is about 4.39g of NaCl added to 500ml of water, which is about the salt content range of heavy saline-alkali land, so the salt concentration in this embodiment conforms to the salinity of normal saline-alkali land. This also provides a theoretical basis for the use of this technical solution in saline-alkali land.

[0157] According to the general calculation of the germination rate of all crops for 72 hours or longer (no more than 7 days), the germination rate of general crops can reach more than 95%; in saline-alkali land, due to the high salt content in the soil, it may be difficult for seeds to germinate or easy to die after germination, so the germination rate of saline-alkali land is usually low, which may be only 60%-70% (Liu Jie et al., 2020). According to the existing technology, the germination rate of crop seeds in mild saline-alkali land is about 70% to 80%, the germination rate of moderate saline-alkali land is not described in detail (Yang Kai, 2020), and the germination rate in severe saline-alkali land is less than 50%. In other words, the germination rate of any crop in severe saline-alkali land will be significantly lower than the germination rate of crops planted in conventional soil.

[0158] Therefore, through comparison, it was found that even in a severely saline-alkali environment, good results can be achieved by treating melon seeds with the tomato straw carbon dot aqueous solution of the present application. The melon root system can reach the growth level in non-saline-alkali land, and the effect is significant.

[0159] In actual use, the tomato straw carbon dot aqueous solution can be used in the process of seed soaking and germination, which can effectively promote the growth and development of melon radicle and lateral roots, improve the resistance of melon plants, and improve their ability to absorb nutrients and increase salt tolerance after planting. By treating melon seeds with the tomato straw carbon dot aqueous solution, the damage caused by salt and alkali to melon plants can be effectively alleviated.

[0160] In addition, after the melon seedlings are transferred to the saline-alkali land for planting, they can be treated with tomato straw carbon dot solution from time to time, which can be sprayed or watered to alleviate the problem of poor melon growth caused by saline-alkali land.

[0161] Example 8: Use of the tomato straw carbon dots prepared in Example 2 as a root promoter

[0162] Soak the selected melon seeds in warm water (50-60℃) for 12 hours, and then sow them in 5×10 plug trays containing substrate for seedling cultivation.

[0163] Among them, soaking seeds in warm water is a commonly used seed treatment method. It uses hot water at a certain temperature to soak seeds to eliminate pathogens lurking on the surface or inside of the seeds, while promoting seeds to absorb water and accelerate germination. This method is simple, economical and effective, and is suitable for seed treatment of a variety of crops.

[0164] The matrix is ​​composed of peat, vermiculite and perlite in a volume ratio of 6:2:2, and water is added and stirred until the matrix forms a ball when held by hand and then falls to the ground and then falls apart. The organic matter content is 45% and the pH is 5.8-6.5.

[0165] After the cotyledons of the melon seedlings are flattened, spray the prepared 150 μg ml for three consecutive days. -1 The carbon dot aqueous solution and the control group (CK) continued to be sprayed with water. After 3 days, it was found that the melon seedlings sprayed with the carbon dot solution had stronger root systems and more vigorous plant growth ( Fig.21 ). Melon seedlings can be transplanted when they have about two leaves and one heart. It takes about 25 days from sowing to transplanting.

[0166] Example 9: Use of the tomato straw carbon dots prepared in Example 2 as a root promoter

[0167] Transplant the melon seedlings into the soil. The specific operation method is: when the melon seedlings grow to two leaves and one heart, use a hole puncher to make planting holes 1 to 2 days in advance, and pour in about 1.5 kg of planting water. After the water in the hole seeps dry, carefully and completely put the melon seedlings into the hole. The depth should be 1 cm below the ridge surface. Use loose fine soil to fix the seedlings. Cover the surface of the soil with 1 cm thick fine dry soil and level it with the ridge surface. After surrounding the soil, water it once more (about 0.5 kg per hole) to make the soil ball in close contact with the surrounding soil. Then, check one by one whether the watering has washed away the soil covering the seedling ball. If it has been washed away, take fine dry soil and cover it again to prevent the root system from being damaged due to excessive water loss of the matrix.

[0168] The roots are easily injured during transplanting, causing root damage. After planting, water once every three days with 150 μg ml -1 The control group CK was irrigated with normal seedling-accelerating water every three days.

[0169] Among them, seedling acclimatization refers to the process in which plants need some time to adapt to the new environment and restore their growth ability after transplanting, repotting or environmental changes. In this process, the plant mainly grows and recovers its root system, while the growth of the above-ground part is not obvious. The duration of seedling acclimatization depends on the type of plant and the specific situation. The seedling acclimatization period of large and woody plants may be longer, lasting from one week to two months; while the seedling acclimatization period of small seedlings and herbaceous plants may be shorter, and it only takes 1-2 days to recover. The seedling acclimatization period of melon is generally about 7 days.

[0170] After 7 days, the transplanted seedlings survived successfully. Compared with the control group (CK) watered with normal seedling water, the transplanted seedlings watered with carbon dot aqueous solution had longer roots, more root hairs, and stronger plant growth ( Fig. 22 ).

[0171] Comparative Example 1

[0172] In order to further prove whether carbon quantum dots prepared from other plants have the same effect on the growth of adventitious roots of melon seedlings, the inventors used cucumber straw (specifically cucumber stems) to prepare corresponding carbon quantum dots (the preparation method is the same as that in Example 2).

[0173] After the roots of the normally growing melon seedlings were cut off, they were placed in 150 μg mL -1 tomato straw carbon dots aqueous solution and 150 μg mL -1 The cucumber straw carbon dots were treated in an aqueous solution for 7 days, and seedlings were randomly selected for phenotype observation. The data were statistically analyzed and the results are shown in Table 2, where CK is water treatment:

[0174] Table 2

[0175]

[0176] According to phenotypic observations, although the carbon quantum dots prepared from cucumber straw promoted the adventitious roots of melon seedlings, their effect was weaker than that of the carbon quantum dots prepared from tomato straw (Table 2).

[0177] The data in Table 2 show that the root length, root surface area, root projection area, root volume, root average diameter, total root tip number, branch number, and intersection number of melon in the TS-CDs treatment group increased by 21.89%, 29.85%, 29.83%, 36.67%, 33.25%, 14.77%, 40.94%, and 44.33% respectively compared with CK. The root length, root surface area, root projection area, root volume, root average diameter, total root tip number, branch number, and intersection number of melon in the CS-CDs treatment group increased by 2.47%, 5.60%, 5.59%, 9.36%, 5.63%, 10.49%, 12.81%, and 1.03% respectively compared with CK. In comparison, the effect of TS-CDs is more significant.

[0178] Comparative Example 2

[0179] Li Jingrui et al. (2020) used the melon variety 'Xizhou Mi No. 25' as the experimental material and used GR24 and IAA to experiment on the growth of melon radicle and adventitious roots. They found that GR24 and IAA treatments had significant regulatory effects in promoting the growth of melon radicle and adventitious roots, and the interactions and concentration effects were obvious.

[0180] GR24 is a chemical substance synthesized on the basis of the framework of Strigol. In 2008, researchers from France, Japan, Australia and other countries confirmed that Strigol can inhibit the branching of the aerial parts of plants together with other hormones, and it is the seventh major type of plant hormone. Due to its instability in the soil, GR24 is currently used more as a research material in the laboratory. Because GR24 is affected by soil temperature and GR24 concentration, the higher the temperature, the faster it degrades, and the higher the concentration, the faster it degrades. Therefore, it is not suitable for conventional agricultural promotion.

[0181] Indole-3-acetic acid (IAA) is a type of plant growth regulator. It is a plant hormone analogue and plays an important role in plant growth and development.

[0182] Since the concentration effect of growth hormone is trace, and it has growth-promoting and growth-inhibiting effects at different concentrations, it is inconvenient to use. The inventors found in their research that the tomato straw carbon dots of the present application can promote growth at a concentration of no more than 200ng / ml.

[0183] At the same time, some growth hormones not only have certain effects on plants, but also affect other organisms to a certain extent after decomposition, affecting the ecological balance. As a carbon source, carbon dots have good safety and stability, and have no suspicion of affecting other organisms while ensuring ecological balance.

[0184] In addition, the price of growth hormone is relatively expensive, which increases unnecessary production costs. Carbon dots, as the main way to utilize waste, greatly reduce production costs, can greatly reduce expenditures in terms of price, increase product revenue, and can be suitable for agricultural promotion.

[0185] In addition, both macroelements and trace elements can promote plant rooting. For example, fertilizers that promote plant rooting are mainly nitro fertilizers, and high nitrogen and high phosphorus can promote root growth (Rui Wenli et al., 2012). However, due to the excessive use of chemical fertilizers and hormone substances, the soil has become seriously salinized, the soil has become compacted, and the soil microbial environment has become disordered, resulting in a decrease in the yield and quality of most fruits, vegetables and crops. Therefore, in the process of field fertilization, organic fertilizers and pollution-free effective substances should be preferred to contribute to the early realization of "carbon neutrality" and "carbon peak". Therefore, the tomato straw carbon dots in the technical solution of this application have good prospects for agricultural promotion.

[0186] The above is a further detailed description of the present invention, which should not be regarded as a limitation on the specific implementation of the present invention. For ordinary technicians in the technical field to which the present invention belongs, simple deduction or replacement without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. A method for preparing tomato straw carbon dots, characterized in that: The following steps are involved: (1) Crush tomato straw; (2) Weigh tomato straw powder, add water in a mass ratio of 1:(90-110), and continue ultrasonic treatment for 25-35 minutes; transfer the suspension to a reactor and heat at 130-200°C for 6-10 hours; (3) centrifuging the obtained mixture at 3000 r / min-8000 r / min for 15-35 min; after centrifugation, collecting the supernatant and filtering it to obtain a liquid product; (4) dialyzing the obtained liquid product; (5) The dialysis solution is freeze-dried to prepare tomato straw carbon dots.

2. The preparation method according to claim 1, characterized in that: In step (2), heating is performed at 160-180° C. for 8-9 h.

3. The preparation method according to claim 1, characterized in that: The filtration in step (3) is vacuum filtration, and the pore size of the filter membrane used in the vacuum filtration is 0.22μm-0.6μm.

4. A tomato straw carbon dot, characterized in that: The raw material for preparing the tomato straw carbon dots is tomato straw, which is obtained by using the preparation method described in any one of claims 1-3.

5. Application of tomato straw carbon dots in promoting plant root growth, characterized in that: The plants include melon.

6. Application of tomato straw carbon dots in promoting plant root growth in saline-alkali soil environment, characterized in that: The plants include melon.

7. A melon root growth promoter, characterized in that: The active ingredient of the root promoter is tomato straw carbon dots, with a concentration of no more than 200 μg ml -1 .

8. A plant growth aid for saline-alkali land environment, characterized in that: The active ingredient of the plant growth aid is tomato straw carbon dots, with a concentration of no more than 200 μg ml -1 .

9. A method for growing melon seedlings, characterized in that: The method comprises soaking seeds and accelerating germination, wherein the concentration used in the soaking and accelerating germination process is 50-200 μg·ml -1 Melon seeds were treated with tomato straw carbon dots aqueous solution.

10. A method for growing plants in a saline-alkali land environment, characterized in that: The method comprises the following steps: during the planting process of plants, treating the seeds of the plants with a tomato straw carbon dot aqueous solution and then transplanting them to saline-alkali land, and / or treating the plant seedlings with a tomato straw carbon dot aqueous solution and then transplanting them to saline-alkali land, and / or watering the plant seeds or plants with a tomato straw carbon dot aqueous solution after planting them in saline-alkali land.

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