Natural plant extract preparation for enhancing salt resistance of corn and application of natural plant extract preparation

Abstract

The invention discloses a natural plant extract preparation for enhancing salt resistance of corn and application of the natural plant extract preparation. According to the preparation, moringa oleifera polysaccharide (MOP) is used as an active ingredient, the stress resistance of corn seedlings under salt stress is remarkably enhanced by irrigating MOP solution with the concentration of 0.05-1.0 g / L at the rhizosphere, and the optimum concentration is 0.2 g / L. The fresh weights of the overground parts and root systems of the corn seedlings can be increased by 127.8% and 53.3% respectively through the concentration treatment; the chlorophyll content is increased by 11.4%, the bound water content is increased by 48.6%, and the potassium-sodium ratio of leaves to soil is remarkably increased; meanwhile, the membrane peroxidation degree is reduced, and the antioxidant enzyme activity is improved. The salt tolerance of the corn is improved through multiple mechanisms of promoting biomass accumulation, enhancing an antioxidant system, improving photosynthetic efficiency, improving water utilization, optimizing ion balance and the like. The preparation is simple to prepare, wide in source, green and environment-friendly, is suitable for stress-resistant cultivation of corn and other crops in saline-alkali soil, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural planting technology, and particularly relates to a MOP preparation for enhancing the salt resistance of corn and application thereof. BACKGROUND

[0002] Land salinization has become an important environmental problem worldwide, severely restricting the sustainable development of agriculture and animal husbandry. How to make full use of salinized land to promote agricultural economic development and improve the ecological environment has become an urgent issue to be solved.

[0003] As an important food crop, corn has moderate salt stress tolerance. Although corn can grow in saline-alkali environments, it will still suffer significant salt stress damage when soil salt stress exceeds a certain threshold. High salt environments can cause water loss from plant cells through osmotic stress, and excessive accumulation of salt ions can cause ion toxicity, disrupting the normal physiological functions of plants. In addition, salt stress can also cause nutrient imbalance in plants, inhibit photosynthesis, accelerate plant aging, and even cause corn to die in severe cases. The combined effects of salt stress significantly affect the growth and yield of corn, becoming an important factor restricting corn production.

[0004] With the continuous growth of global food demand and the continuous expansion of corn planting area, improving the salt resistance of corn has become a key issue in current agricultural technology. Existing salt resistance technologies mainly rely on corn breeding, soil conditioning and exogenous regulation. However, breeding technology has the problems of long cycle and slow effect; soil conditioning agents can improve the soil environment, but their application amount is large, the cost is high, the engineering quantity is large, and the improvement of large-area saline-alkali land still faces great challenges. Therefore, it is urgent to develop an efficient, low-cost, convenient-to-apply and rapid-acting salt resistance technology.

[0005] Studies have shown that salt stress mainly affects plants through three ways: ion toxicity, nutrient imbalance and physiological drought. These salt stresses can damage the integrity of plant cell membranes, generate oxidative damage substances such as malondialdehyde, and cause oxidative damage to plants. Although the antioxidant enzyme system in plants (such as superoxide dismutase, peroxidase, etc.) can remove free radicals to some extent and alleviate oxidative damage, existing water and soil management and chemical improvement methods are often costly and have limited effect. Compared with traditional salt resistance breeding and soil conditioning methods, exogenous regulation methods (such as rhizosphere or foliar application of regulating agents) show significant advantages in light to moderate salt stress soils. These methods have short cycles, low labor requirements, and are easy to apply, with low cost and rapid effectiveness. Therefore, exogenous regulation technology provides an effective and economical solution under light to moderate salt stress conditions.

[0006] Moringa Oleifera Polysaccharide (MOP) is a natural polysaccharide extracted from the leaves of Moringa oleifera, a tropical deciduous tree native to India. Widely used in traditional medicine, MOP has been extensively studied and recognized in the medical and health care fields for its multiple biological activities as a major functional ingredient of natural plant extracts. Its known effects include lowering blood sugar and blood lipids, antioxidant, enhancing immunity, delaying aging, and anti-tumor, etc. In recent years, due to its natural origin, high safety and significant activity, MOP has attracted increasing attention in various fields. From the chemical composition, MOP is rich in isothiocyanate, flavonoids, polyphenols, phenolic acids and other active substances, with strong antioxidant properties. These components can effectively scavenge free radicals generated in plants under stress, slow down the lipid peroxidation process, thereby protecting the plant cell membrane structure and reducing oxidative damage. In addition, the natural plant hormones and osmotic regulation substances contained in MOP can help improve the plant's adaptability to abiotic stress such as drought, salinity and low temperature. Studies have shown that MOP can significantly enhance the overall stress resistance of plants by regulating the osmotic balance and activating antioxidant enzyme systems (such as superoxide dismutase and peroxidase).

[0007] Currently, the main application fields of MOP in China are concentrated in nutritional food, health tea and animal feed, etc. Especially in the production of livestock and poultry, studies have shown that it can significantly improve the growth performance and immune function of animals. However, the application of natural plant extracts in crop salt-tolerance regulation, especially in food crops such as corn, has not been systematically studied or reported in public literature.

[0008] As a moderately salt-tolerant food crop, corn faces multiple stresses when planted in saline-alkali land, including physiological drought, ion toxicity and nutrient imbalance. The existing traditional breeding techniques and soil improvement methods have limitations in efficiency and cost, and are difficult to promote in a wide range of saline-alkali land. Therefore, the development of a natural, safe, environmentally friendly, and potentially antioxidant and osmotic regulation exogenous regulatory substance has become a practical demand to solve the problem of corn salt tolerance. SUMMARY

[0009] The present application first attempts to apply MOP to the regulation of corn salt stress, providing a green, efficient and low-cost new technology for corn planting in saline-alkali land, in order to promote the sustainable growth of corn in saline-alkali land environment, improve crop salt tolerance and increase yield.

[0010] To achieve the above-mentioned application purposes, the present application provides the following technical solutions: In a first aspect, the present application provides a method for enhancing the salt resistance of corn, comprising: applying a natural plant extract preparation to the rhizosphere; the active ingredient of the natural plant extract preparation is moringa polysaccharide. By applying the natural plant extract (MOP) to the rhizosphere, the growth vigor and stress resistance of corn seedlings under salt stress conditions are significantly enhanced.

[0011] The natural plant extract preparation is an aqueous solution, wherein the concentration of moringa polysaccharide is 0.05-1.0 g / L, preferably the concentration is 0.1-0.5 g / L, and more preferably the concentration is 0.2 g / L. By optimizing the concentration, the salt resistance effect can be significantly improved.

[0012] The application conditions of the rhizosphere irrigation are as follows: 25-35 mL of the natural plant extract preparation is applied to each corn, and the irrigation frequency is once every 2-4 days, and the irrigation is continuously applied for 2-4 times.

[0013] The rhizosphere irrigation starts about 7 days after the corn seedlings emerge, and the corn seedlings are seedlings growing to 2-4 true leaf stages.

[0014] The dosage form of the natural plant extract preparation is aqueous solution, powder (including soluble powder, wettable powder), granules, water dispersible granules, suspension, microemulsion, emulsion, concentrated solution, slow-release agent, etc.

[0015] Aqueous solution: direct dissolution for use (consistent with the experiment); powder / soluble powder: convenient for storage and transportation, and dissolved for use; granules / water dispersible granules: more stable and convenient to use; suspension: suitable for poorly soluble ingredients; microemulsion / emulsion: improve bioavailability; slow-release agent: prolong the action time and reduce the application frequency.

[0016] The corn is corn planted in saline-alkali soil.

[0017] The method of the present application is suitable for mild to moderate saline-alkali soil (EC value 1.0-4.0 mS / cm); or for coastal saline-alkali soil with sodium salt as the main salt type, and the pH value is in the neutral to weak alkaline range (7.5-8.5).

[0018] In a second aspect, the present application provides a natural plant extract preparation for improving the salt resistance of corn, comprising the following components: active ingredient and excipient; the active ingredient is moringa polysaccharide (MOP).

[0019] In the natural plant extract preparation, the concentration of moringa polysaccharide is 0.05 g / L-1.0 g / L.

[0020] Compared with the prior art, the present application has the following beneficial effects: The system research found that the MOP preparation had obvious concentration dependence on the salt tolerance of corn in the concentration range of 0.05-1.0 g / L, and the comprehensive optimum concentration was 0.2 g / L. The biomass accumulation of corn seedlings was significantly promoted under the treatment of this concentration, and the fresh weight of aboveground and root increased by about 127.8% and 53.3%, respectively; at the same time, the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in leaves were reduced, the membrane lipid peroxidation damage was reduced, and the cell membrane stability was improved. MOP treatment also significantly increased the hydroxyl radical clearance rate, superoxide dismutase (SOD) and catalase (CAT) activities, enhanced the antioxidant defense system, and maintained the cell redox balance; the increase of SPAD value indicated the enhancement of chlorophyll synthesis and photosynthesis capacity. Although there was no significant difference in chlorophyll fluorescence parameters (Fv / Fm, Fv / Fo), the overall trend was upward, showing the potential for improvement of photochemical efficiency.

[0021] In addition, MOP treatment significantly optimized the water binding form of corn seedling leaves, reduced the free water content by 59.5%, increased the bound water content by 48.6%, and effectively improved the cell structure stability. The soil analysis results showed that the 0.1-0.2 g / L MOP treatment increased the soil exchangeable potassium content, reduced the exchangeable sodium content, increased the potassium-sodium ratio by 17.7%, and improved the soil ion environment. Plant ion analysis further showed that MOP promoted the absorption and transportation of potassium ions to leaves, inhibited the excessive accumulation of sodium ions in leaves, significantly increased the potassium-sodium ratio in leaves, and optimized the ion balance mechanism of plants, thereby enhancing the ion homeostasis regulation ability under salt stress.

[0022] Overall, MOP preparation significantly enhanced the salt tolerance and growth performance of corn seedlings under salt stress through multiple mechanisms, including promoting biomass accumulation, enhancing antioxidant system, improving photosynthetic efficiency, improving water utilization, and regulating soil-plant ion balance. The preparation of this technology is simple, widely available, non-toxic and environmentally friendly, and is suitable for the stress resistance cultivation and management of corn and other crops in saline-alkali land, and has good ecological popularization value and application prospect. DETAILED DESCRIPTION

[0023] The application will be further described below in conjunction with specific examples, but the application is not limited to the following examples.

[0024] In the following examples, the experimental methods used are conventional methods unless otherwise specified.

[0025] In the following examples, the reagents, materials, instruments, etc. used are commercially available unless otherwise specified.

[0026] Unless otherwise defined, all terms (such as "salt stress", "rhizosphere irrigation", "antioxidant enzyme activity", etc.) used in the present invention are used according to the common definition in the field of agricultural science and plant physiology. "And / or" in the specification means the combination of any one or more of the listed items.

[0027] The present inventors found through systematic research that MOP has obvious growth promotion and stress regulation effects on salt-stressed corn seedlings within a concentration range of 0.05 g / L to 1.0 g / L. Through rhizosphere irrigation treatment, MOP can significantly promote the biomass accumulation of corn seedlings, improve root development, reduce membrane lipid peroxidation levels, enhance antioxidant enzyme activity and free radical scavenging capacity, and at the same time, increase chlorophyll content and photochemical efficiency, improve water binding form and ion balance state of the plant, thereby effectively enhancing the adaptability of corn seedlings to saline-alkali environment. The method uses MOP as the core active component, is green and safe, and is biodegradable, and has good ecological application value.

[0028] Some embodiments of the present invention disclose the application of MOP preparations in enhancing the salt resistance of corn seedlings, using rhizosphere irrigation to relieve salt stress.

[0029] In some embodiments, the concentration range of the MOP preparation used is 0.05 g / L to 1.0 g / L.

[0030] In other embodiments, the concentration range of the MOP preparation used is 0.05 g / L to 0.75 g / L.

[0031] In preferred embodiments, the concentration of MOP used is 0.1 g / L to 0.5 g / L, with 0.2 g / L being the most suitable concentration. At this concentration, MOP shows the best overall effect in promoting biomass growth, enhancing antioxidant defense, optimizing photosynthesis, improving water status, and regulating soil and plant potassium and sodium ion balance.

[0032] Some embodiments of the present invention also disclose a preparation for improving the salt resistance of corn, the active ingredient of which is MOP, which can be directly dissolved in distilled water to prepare a working solution.

[0033] The preparation method of the preparation comprises: accurately weighing MOP powder, dissolving it in distilled water, controlling the concentration of the solution within the range of 0.05 g / L to 1.0 g / L, and thoroughly stirring until completely dissolved to obtain a working solution that can be used for rhizosphere irrigation.

[0034] The application method of the preparation comprises: rhizosphere irrigation of the above-mentioned solution to improve the salt resistance of corn seedlings. Rhizosphere irrigation allows the active ingredient to act directly on the root zone, regulates soil ion balance and activates the antioxidant system of the plant, thereby enhancing the salt tolerance of the plant.

[0035] In a preferred embodiment, the corn seedlings are irrigated when they are about 7 days old and have grown to the stage of 2-3 true leaves. At this stage, the root system of the plants has developed preliminarily stable and is sensitive to rhizosphere regulation and response, facilitating the absorption and utilization of active ingredients.

[0036] In another embodiment, the irrigation timing is the initial stage of salt stress, and the treatment is performed when the plants show slight water loss or the leaf tips turn yellow. Each corn seedling is irrigated with 25-35 mL of MOP solution of the corresponding concentration, ensuring that the solution is uniformly distributed in the rhizosphere area; the irrigation frequency is once every 2-4 days, and the treatment is performed for 2-4 times. All treatments are performed between 9:00 and 10:00 in the morning to avoid the influence of high temperature and strong light on the absorption effect.

[0037] In a preferred aspect of the present application, the 0.2 g / L MOP irrigation treatment can significantly increase the fresh weight of the aboveground and root systems of corn seedlings under salt stress, reduce the MDA and H2O2 contents of the leaves, increase the SOD and CAT activities, hydroxyl radical removal rate, SPAD value, and photochemical efficiency, optimize the ratio of free water to bound water, and maintain ion homeostasis by increasing the soil to plant potassium to sodium ratio, thereby significantly enhancing the salt tolerance and growth performance of corn seedlings.

[0038] In the following examples: The MOP powder used is purchased from Xi'an Ruierli Biological Engineering Co., Ltd.

[0039] The corn seeds are Nongke Nuo 336, purchased from Jingyan Yinan Beijing Seed Technology Co., Ltd.

[0040] The saline-alkali soil sample is collected from a wheat field soil in Huanghua coastal area, Hebei Province, and the soil texture is coastal fluvo-aquic soil, the pH value is 7.8, the EC value is 1.5 mS / cm, the exchangeable sodium is 0.61 cmol / kg, the exchangeable potassium is 0.67 cmol / kg, and it belongs to a typical coastal mild saline-alkali soil, which is suitable for studying the promotion of exogenous substances on the growth and development of corn under mild salt stress.

[0041] The present application is described in detail below in combination with the attached table and specific examples.

[0042] Example 1: A preparation, method and application for improving the salt tolerance of corn seedlings In this embodiment, the preparation for improving the salt tolerance of corn seedlings is a MOP solution with a concentration of 0.1 g / L.

[0043] Preparation method: accurately weigh 0.100 g of MOP powder and dissolve it in 1 L of sterile distilled water to obtain the required solution.

[0044] Use method: after the corn seedlings emerge for 7 days, adopt rhizosphere irrigation method, irrigate 30-35 mL solution per plant, irrigate once every 3 days, irrigate for 3 times continuously, keep the soil humidity at 70%-80% of the field water holding capacity.

[0045] Example 2: A preparation, method and application for improving the salt resistance of corn seedlings In this embodiment, the preparation for improving the salt resistance of corn seedlings is a MOP solution with a concentration of 0.2 g / L.

[0046] Preparation method: accurately weigh 0.200 g of MOP powder, dissolve in 1 L of sterile distilled water, and the required solution is obtained.

[0047] Use method: after the corn seedlings emerge for 7 days, adopt rhizosphere irrigation method, irrigate 30-35 mL solution per plant, irrigate once every 3 days, irrigate for 3 times continuously, keep the soil humidity at 70%-80% of the field water holding capacity.

[0048] Example 3: A preparation, method and application for improving the salt resistance of corn seedlings In this embodiment, the preparation for improving the salt resistance of corn seedlings is a MOP solution with a concentration of 0.5 g / L.

[0049] Preparation method: accurately weigh 0.500 g of MOP powder, dissolve in 1 L of sterile distilled water, and the required solution is obtained.

[0050] Use method: after the corn seedlings emerge for 7 days, adopt rhizosphere irrigation method, irrigate 30-35 mL solution per plant, irrigate once every 3 days, irrigate for 3 times continuously, keep the soil humidity at 70%-80% of the field water holding capacity.

[0051] Example 4: Control treatment (CK) In this embodiment, no MOP is added, only the same volume of deionized water is irrigated, and the rest of the conditions are consistent with each treatment group, which is used to compare the influence of MOP at different concentrations on the salt resistance and physiological and biochemical indexes of corn seedlings.

[0052] Test example MOP's influence on the physiological and biochemical indexes of salt stressed corn I. Experimental method The specific steps of the corn salt resistance experiment are as follows: Soil physical and chemical index determination: pH value is determined by potential method (water-soil ratio 1:2.5), EC value is determined by conductance method (water-soil ratio 1:5), exchangeable potassium and sodium are determined by ammonium acetate extraction-flame photometry, and total salt content is determined by residue drying method.

[0053] Experimental conditions and environment: The study was conducted in the greenhouse of Beijing Academy of Agriculture and Forestry Sciences, and the corn seedlings were planted by pot culture. The saline-alkali soil used in the experiment was sieved through a 2 mm sieve, then water was added and stirred until it was moderately moist. Each pot was sown with 2 full and uniform corn seeds in the center, then covered with soil and sprayed with water to keep it moist, and covered with plastic film to keep it moist. After germination, replace with newspaper covering, and when the plants grow to 2 leaves 1 heart stage, remove the covering to adapt to natural light conditions.

[0054] Four treatment gradients were set up, namely MOP 0 (CK), 0.1, 0.2, 0.5 g / L. The treatment used rhizosphere irrigation with MOP, each plant was irrigated with 25-35 mL of corresponding concentration solution, at 9:00-10:00 in the morning, with an interval of 2-4 days, a total of 2-4 times; the control group was replaced with the same volume of deionized water. During the experiment, the soil water content was maintained at 70%-80% of the field water capacity by adding water to ensure that the soil humidity was stable during the test process and to avoid errors caused by dry and wet changes.

[0055] Three days after the last irrigation treatment, corn seedling leaves were collected for determination of photosynthesis and physiological and biochemical indicators. Leaf photosynthetic fluorescence parameters (Fo, Fm, Fv, Fv / Fm, Fv / Fo, ABS / RC, TRo / RC, ETo / RC, DIo / RC) were determined using a PAM-2500 type chlorophyll fluorometer; SPAD value was determined using a SPAD-502 chlorophyll meter to reflect the change of chlorophyll content; water binding form (free water and bound water) was determined by drying weight difference method to evaluate the leaf water state and cell structure stability. Oxidative stress and antioxidant indicators include malondialdehyde (MDA), hydrogen peroxide (H2O2), hydroxyl radical clearance rate and antioxidant enzymes SOD and CAT activity, which were determined by enzyme marker method.

[0056] The corn seedling plants were harvested 1 week after the treatment ended, and were divided into aboveground and root parts using stainless steel scissors, washed and dried to determine the fresh weight of the aboveground and root parts to calculate the biomass and root-shoot ratio. After drying and crushing, the K + , Na + content and K / Na ratio of plant leaves and roots were determined by inductively coupled plasma mass spectrometry (ICP-MS) to analyze the regulation of MOP on ion absorption and distribution. At the same time, the corresponding potting soil samples were collected to determine the soil exchangeable potassium, sodium content and potassium-sodium ratio to evaluate the improvement effect of MOP on ion balance of saline-alkali soil.

[0057] II. Index detection 1. Aboveground and root biomass of corn seedlings The effect of rhizosphere irrigation with different concentrations of MOP on the growth of corn under salt stress is shown in Table 1.

[0058] Table 1 Fresh weight of corn seedling shoots and roots

[0059] The results showed that, compared with the control, MOP treatment significantly promoted the growth of corn seedlings within a certain concentration range. Among them, the treatment of 0.2 g / L MOP had the most significant effect, with the fresh weight of shoots increasing by about 127.8% and the fresh weight of roots increasing by about 53.3%, reaching a statistically significant level. The treatment of 0.1 g / L MOP also showed a promoting effect, with the fresh weight of shoots increasing by about 72.2% and the fresh weight of roots increasing by about 40.0%. However, when the concentration of MOP increased to 0.5 g / L, the growth-promoting effect was weakened, with the fresh weight of shoots and roots increasing by about 55.6% and 20.0%, respectively, indicating that the promoting effect of MOP on corn seedling growth was concentration-dependent, with 0.2 g / L being the optimal concentration. The root-shoot ratio of corn seedlings in each treatment group showed a decreasing trend compared with the control, but did not reach a statistically significant level. The above data showed that MOP rhizosphere irrigation treatment helped to promote the growth of salt-stressed corn seedlings and increase the biomass of salt-stressed corn seedlings, with the best effect at a concentration of 0.2 g / L.

[0060] MDA and H2O2 in salt-stressed corn seedling leaves MDA (malondialdehyde) and H2O2 (hydrogen peroxide) are important physiological indicators for evaluating plant salt tolerance. H2O2, as a reactive oxygen species produced by excess light energy caused by salt stress, can exacerbate cell membrane lipid peroxidation, leading to an increase in MDA and H2O2 content, and thus damage the selectivity and permeability of the cell membrane.

[0061] The MDA and H2O2 contents in corn seedling leaves were determined by enzyme labeling instrument method, and the analysis results are shown in Table 2.

[0062] Table 2 H2O2 and MDA in corn seedling leaves

[0063] The results showed that different concentrations of MOP treatment all showed a trend of reducing the content of MDA and H2O2 in the leaves of salt-stressed maize seedlings. Among them, the effect of 0.2 g / L MOP treatment was the most obvious, the H2O2 content of maize seedling leaves decreased from 3.62±0.11 μmol / g to 3.04±0.87 μmol / g, decreased by about 16.0%; the MDA content decreased from 255.2±27.6 nmol / g to 227.9±50.3 nmol / g, decreased by about 10.7%. 0.1 g / L MOP treatment also showed a certain alleviating effect, the H2O2 content decreased to 3.24±0.78 μmol / g, decreased by about 10.5%, and the MDA content decreased to 236.1±32.4 nmol / g, decreased by about 7.5%. However, when the concentration of MOP increased to 0.5 g / L, the H2O2 content increased to 3.68±0.61 μmol / g, slightly higher than the control level, and the MDA content was 243.7±55.3 nmol / g, only decreased by about 4.5%, indicating that high concentration of MOP weakened the effect of alleviating oxidative stress. Although the data between each treatment group did not reach the statistical significant difference level (p>0.05), the 0.2 g / L concentration treatment showed the best trend in reducing ROS accumulation and membrane lipid peroxidation degree. The above data showed that the rhizosphere irrigation treatment of MOP at an appropriate concentration (0.2 g / L) could help to reduce the ROS accumulation in the leaves of salt-stressed maize seedlings, reduce the degree of leaf membrane lipid peroxidation, and improve the stability of cell membrane, which helped to enhance the tolerance of maize seedlings to salt stress.

[0064] Hydroxyl radical scavenging capacity and antioxidant enzyme activity of salt-stressed maize seedling leaves Strong hydroxyl radical scavenging capacity is of great significance for plants to resist oxidative stress in adversity. SOD (superoxide dismutase) and CAT (catalase) are key defense factors for plants to cope with adversity, and are usually positively correlated with the antioxidant regulation capacity of plants. In this experiment, the kit provided by Beijing Solabio Science and Technology Co., Ltd. was used.

[0065] The hydroxyl radical scavenging capacity, SOD activity and CAT activity of maize seedlings were determined by enzyme marker method.

[0066] Table 3 Hydroxyl radical scavenging capacity and antioxidant enzyme activity of maize seedling leaves

[0067] The results (Table 3) showed that the effects of different concentrations of MOP on the antioxidant system of maize seedlings under salt stress showed a concentration-dependent characteristic. Both 0.1 g / L and 0.2 g / L MOP treatments significantly increased the hydroxyl radical scavenging capacity of maize seedlings, with 0.2 g / L treatment being the best, increasing the leaf hydroxyl radical scavenging rate from 37.9±8% to 65.3±8.2%, an increase of about 72.3% (p<0.05); the 0.1 g / L treatment reached 59.5±9.4%, an increase of about 57.0% (p<0.05). However, when the concentration increased to 0.5 g / L, the hydroxyl radical scavenging rate decreased to 42.8±7.2%, with no significant difference from the control, indicating that high concentration of MOP weakened the promotion effect on hydroxyl radical scavenging capacity.

[0068] In terms of antioxidant enzyme activity, MOP treatment significantly increased the activities of two key enzymes, SOD and CAT, in leaves. SOD activity showed a clear concentration effect: SOD activity increased significantly from 38.5±7.8 U / g to 70.9±11 U / g under 0.2 g / L treatment, an increase of about 84.2% (p<0.05), which was the optimal concentration; 0.5 g / L and 0.1 g / L treatments reached 51.8±17.9 U / g and 46.8±10 U / g, respectively, with increases of about 34.5% and 21.6%. CAT activity showed an increasing trend with increasing MOP concentration, with the highest value of 850.1±135.7 U / (g·min) under 0.5 g / L treatment, an increase of about 161.0% (p<0.05); 0.2 g / L treatment reached 695.9±177.2 U / (g·min), an increase of about 113.7% (p<0.05); 0.1 g / L treatment reached 539.2±180 U / (g·min), an increase of about 65.5%.

[0069] Comprehensive analysis showed that the optimal concentration of MOP treatment for different antioxidant indicators was different: 0.2 g / L concentration was the best for improving hydroxyl radical scavenging capacity and SOD activity, while 0.5 g / L concentration was the most significant for promoting CAT activity. Overall, 0.2 g / L MOP treatment showed a more balanced promotion effect on the three indicators of hydroxyl radical scavenging capacity, SOD and CAT activity, effectively maintaining the redox balance, reducing oxidative stress and cell oxidative damage, and thus enhancing the salt tolerance of salt-stressed maize seedlings.

[0070] Fluorescence series parameters of maize seedling leaves Chlorophyll fluorescence parameters have important significance in the study of plant stress resistance. Fv / Fo and Fv / Fm as core indicators can directly reflect the potential and actual photochemical activity of plant photosystem II under stress conditions, and monitor the operation state of plant photosystem efficiently. The changes of Fo, Fm, Fv and other parameters reveal the dynamic response of photosynthetic organs to stress and provide early signals of stress damage. At the same time, ABS / RC, TRo / RC, ETo / RC and DIo / RC and other parameters can accurately analyze the absorption, transmission and dissipation process of light energy, helping to understand how plants adjust photosynthetic strategy to maintain growth under stress. These parameters provide scientific basis for exploring plant stress resistance mechanism. The results of photosynthetic fluorescence series parameters analysis of corn seedling leaves are shown in Table 4 and Table 5.

[0071] Table 4 Chlorophyll fluorescence parameters and photochemical efficiency of corn seedling leaves

[0072] Table 5 Light energy absorption, transmission and utilization of corn seedling leaves

[0073] The results showed that the effects of different concentrations of MOP on the photochemical efficiency parameters of corn seedling leaves showed a certain concentration-dependent characteristic. Compared with the control, 0.1 g / L and 0.2 g / L MOP treatment showed no significant difference in Fo, Fm, Fv, Fv / Fo and Fv / Fm of corn seedling leaves, but showed an improvement trend. Among them, 0.1 g / L treatment increased Fv, Fv / Fo and Fv / Fm by 5.67%, 5.80% and 1.15% respectively, showing the most obvious effect; 0.2 g / L treatment increased Fv, Fv / Fo and Fv / Fm by 4.79%, 5.88% and 1.28% respectively; while 0.5 g / L treatment increased Fv, Fv / Fo and Fv / Fm by only 1.46%, 3.29% and 0.64% respectively, and the improvement effect weakened. These data suggested that appropriate concentration of MOP rhizosphere irrigation treatment had the potential to improve the photochemical efficiency of corn seedling leaves under salt stress, and 0.1-0.2 g / L was the more appropriate concentration range The regulation of MOP treatment on various parameters also showed concentration effect in terms of light energy absorption, transmission and utilization. The ABS / RC and TRo / RC of corn seedling leaves treated with 0.2 g / L MOP increased by 4.41% and 3.09% respectively, with the largest increase, indicating that it enhanced the absorption and capture ability of light energy; ABS / RC and TRo / RC treated with 0.1 g / L increased by 1.97% and 1.89% respectively; ABS / RC and TRo / RC treated with 0.5 g / L increased by 1.64% and 1.01% respectively. While ETo / RC decreased in the three concentrations, with 0.2 g / L treatment decreased by 3.46%, 0.1 g / L treatment decreased by 2.16%, and 0.5 g / L treatment decreased by 1.84%, which may imply that the efficiency of light energy transmission has decreased, which is speculated to be related to the blockage of energy transmission. At the same time, DIo / RC showed an increasing trend with the increase of MOP concentration, with 0.2 g / L treatment increased by 9.17%, 0.1 g / L treatment increased by 2.08%, and 0.5 g / L treatment increased by 3.81%, indicating that the energy dissipation has been enhanced. Although there was no statistically significant difference between the treatment groups (p>0.05), 0.2 g / L concentration showed the most obvious change trend in regulating light energy utilization parameters.

[0074] SPAD value detection of corn seedling leaves Salt stress usually inhibits the synthesis of chlorophyll in plants, and thus affects the efficiency of photosynthesis. To evaluate the effect of MOP on the photosynthesis of corn seedlings, the SPAD value of corn seedling leaves was detected using SPAD-502 type chlorophyll meter.

[0075] Chlorophyll content is an important indicator of plant photosynthetic capacity, and SPAD value can effectively reflect the chlorophyll content and photosynthetic capacity of plants. The SPAD value detection results of corn seedling leaves are shown in Table 5. The results show that the effects of different concentrations of MOP treatment on the SPAD value of corn seedling leaves are significantly different. Compared with the control group (31.5±2.9), the SPAD value of corn seedling leaves treated with 0.2 g / L MOP solution was significantly increased, reaching 35.1±5.1, with an increase of 11.4% (p<0.05), and the effect was the most significant. The SPAD value of 0.1 g / L MOP treatment was 30.9±1.8, which was basically the same as the control, and decreased by 1.9%. It is worth noting that when the concentration of MOP increased to 0.5 g / L, the SPAD value decreased to 27.9±4.5, which was 11.4% lower than the control (p<0.05), indicating that high concentration of MOP had an inhibitory effect on the synthesis of chlorophyll in corn seedling leaves. In summary, the rhizosphere irrigation treatment of MOP at an appropriate concentration (0.2 g / L) can effectively improve the chlorophyll synthesis of salt-stressed corn seedling leaves and enhance the photosynthetic capacity of corn seedling plants, but high concentration (0.5 g / L) treatment has a negative effect, further confirming the concentration-dependent characteristics of MOP on the photosynthetic physiology of corn seedlings.

[0076] Free water and bound water content of salt-stressed corn seedling leaves The free water and bound water content in plants is closely related to their physiological metabolism and stress resistance. Free water is a good solvent in cells and participates in various biochemical reactions. Higher free water content usually indicates that the plant metabolism is active and the cell physiological process is vigorous, which is beneficial to growth and development. Bound water is closely related to the structural stability of cells, and higher bound water content usually indicates that plant cells have stronger stress resistance and can maintain the stability of cell structure and function under adverse conditions such as drought, high temperature, and low temperature, reducing water loss and cell damage. The results of plant water binding form analysis are shown in Table 6.

[0077] Table 6 Free water and bound water content of corn seedling leaves

[0078] The results showed that the regulation of different concentrations of MOP on the water combination form of maize seedling leaves under saline-alkali soil planting conditions showed a significant concentration-dependent effect. Compared with the control, all MOP treatments significantly reduced the free water content of maize seedling leaves, while significantly increasing the bound water content. Among them, the 0.2 g / L MOP treatment had the most significant regulation effect, the free water content of the leaves decreased from 0.42±0.03% to 0.17±0.03%, a decrease of about 59.5% (p<0.05), with the largest decrease; the bound water content increased from 0.37±0.03% to 0.55±0.05%, an increase of about 48.6% (p<0.05), with the highest increase. The 0.1 g / L MOP treatment also showed obvious regulation effect, the free water content decreased to 0.28±0.03%, a decrease of about 33.3% (p<0.05); the bound water content increased to 0.48±0.08%, an increase of about 29.7% (p<0.05). When the MOP concentration increased to 0.5 g / L, the free water content decreased to 0.32±0.1%, a decrease of about 23.8% (p<0.05); the bound water content was 0.47±0.08%, an increase of about 27.0% (p<0.05), the regulation effect was weaker than that of 0.2 g / L treatment, but still better than the control.

[0079] The comprehensive analysis showed that MOP treatment effectively regulated the water combination form in plant body by significantly reducing the free water content and increasing the bound water content of maize seedling leaves, thereby slowing down plant metabolism, enhancing plant cell structure stability, and improving the salt tolerance of maize seedlings. Among them, 0.2 g / L was the most suitable concentration, which showed the best effect in reducing free water content and increasing bound water content, and could more effectively help maize seedlings maintain cell function stability and enhance adversity adaptation ability under salt stress conditions.

[0080] Soil exchangeable potassium and sodium content and ratio Soil exchangeable potassium and sodium content and ratio are important indicators for evaluating the fertility status of saline-alkali soil and the degree of salt stress. Exchangeable potassium, as an essential macronutrient for plants, not only participates in various physiological metabolic processes in plants, but also plays a key role in osmoregulation and ion balance. High exchangeable sodium content is one of the main characteristics of saline-alkali soil, and excessive sodium ions can damage soil structure, inhibit the absorption of nutrients such as potassium by plants, and have toxic effects on plants. The ratio of soil potassium to sodium is a comprehensive indicator of soil ion balance. A higher potassium to sodium ratio generally indicates a lighter degree of soil salinization, which is beneficial to the absorption of nutrients by plant roots and growth and development, and can also alleviate the stress effects of sodium ions on plants. Therefore, optimizing the ratio of soil potassium to sodium is of great significance for improving the saline-alkali soil environment and enhancing the salt tolerance of crops. The results of the determination of soil exchangeable potassium, exchangeable sodium content and potassium to sodium ratio are shown in Table 7.

[0081] Table 7 Soil potassium and sodium content and ratio

[0082] In terms of soil exchangeable potassium content, different concentrations of MOP treatment showed a certain trend. Compared with the control (0.669±0.047 cmol / kg), the 0.1 g / L MOP treatment had the most obvious effect, with an exchangeable potassium content of 0.705±0.018 cmol / kg, an increase of about 5.4% compared with the control; the 0.5 g / L and 0.2 g / L treatments were 0.697±0.041 cmol / kg and 0.686±0.004 cmol / kg, respectively, an increase of about 4.2% and 2.5% compared with the control. However, the difference between the treatment groups did not reach a statistically significant level (p>0.05).

[0083] In terms of soil exchangeable sodium content, MOP treatment showed a trend of reducing soil exchangeable sodium. The 0.1 g / L treatment had the most significant reduction effect, with an exchangeable sodium content of 0.551±0.060 cmol / kg, a decrease of about 9.7% compared with the control (0.610±0.049 cmol / kg); the 0.5 g / L and 0.2 g / L treatments were 0.586±0.017 cmol / kg and 0.590±0.034 cmol / kg, respectively, a decrease of about 3.9% and 3.3%, respectively. The difference between the treatment groups did not reach a statistically significant level (p>0.05).

[0084] In terms of soil potassium and sodium ratio, the 0.1 g / L MOP treatment significantly increased the soil potassium and sodium ratio, from 1.099±0.025 in the control to 1.293±0.166, an increase of about 17.7% (p<0.05), with the most significant effect; the 0.5 g / L and 0.2 g / L treatments had potassium and sodium ratios of 1.189±0.042 and 1.166±0.064, respectively, an increase of about 8.2% and 6.1% compared with the control, but not reaching a significant level. In summary, MOP treatment effectively improved the soil potassium and sodium ratio by increasing the exchangeable potassium content and reducing the exchangeable sodium content, with 0.1 g / L being the most suitable concentration, and the best effect on optimizing the ion balance of saline-alkali soil and relieving sodium salt stress.

[0085] Plant root and leaf potassium and sodium content and ratio The contents of potassium and sodium ions and their ratio in plant roots and leaves are key physiological indicators reflecting plant salt tolerance and nutrient absorption capacity. Potassium ion is an essential macronutrient for plant growth and development, and is involved in important physiological processes such as photosynthesis, enzymatic reactions, and osmotic regulation. Excessive accumulation of sodium ions under salt stress can disrupt cell ion balance, inhibit potassium ion absorption and transport, cause ion toxicity, damage cell membrane structure and enzyme activity, and ultimately affect normal plant growth. The potassium-to-sodium ratio in plants is an important indicator for evaluating plant salt tolerance. A higher potassium-to-sodium ratio indicates that the plant has a stronger ability to selectively absorb potassium ions, reject or compartmentalize sodium ions, maintain ion homeostasis in cells, and ensure normal physiological metabolism. The root system, as the main organ for nutrient absorption, directly reflects the selective absorption characteristics of plants to soil ions through its potassium-to-sodium ratio. The leaf potassium-to-sodium ratio reflects the coordination ability of ion transport and distribution in plants. Therefore, analyzing the potassium and sodium contents and their ratio in plant roots and leaves is of great significance for understanding plant salt tolerance mechanisms and evaluating the effectiveness of salt-resistant treatments. The results of the determination of potassium and sodium contents and their ratio in the shoots and roots of maize seedlings are shown in Table 8.

[0086] Table 8 Potassium and sodium contents and their ratio in the shoots and roots of maize seedlings

[0087] In terms of potassium ion content and distribution, the effects of different concentrations of MOP on leaf potassium content showed a significant concentration-dependent manner. The leaf potassium content reached the highest value of 51.666 ± 3.728 g / kg under 0.5 g / L treatment, which was significantly higher than that of the control (25.514 ± 1.420 g / kg) by about 102.5% (p < 0.05). The leaf potassium contents under 0.1 and 0.2 g / L treatments were 33.969 ± 1.949 and 34.238 ± 2.550 g / kg, respectively, which were significantly higher than that of the control by about 33.1% and 34.2% (p < 0.05). The root potassium content slightly increased to 10.523 ± 0.491 g / kg under 0.1 g / L treatment, while it decreased to 8.923 ± 0.481 and 8.627 ± 0.605 g / kg under 0.2 and 0.5 g / L treatments, respectively. The leaf-to-root potassium ratio significantly increased with increasing MOP concentration, reaching 5.986 ± 0.604 under 0.5 g / L treatment, which was about 139.7% higher than that of the control (p < 0.05), indicating that MOP promoted the transport of potassium ions to the shoots.

[0088] In terms of sodium ion content and distribution, the 0.5 g / L treatment significantly increased leaf sodium content to 7.197 ± 0.787 g / kg (p < 0.05), while the 0.1 and 0.2 g / L treatments had no significant difference in leaf sodium content compared to the control. Root sodium content was significantly increased to 16.510 ± 0.977 g / kg (p < 0.05) under the 0.1 g / L treatment, indicating that this concentration promoted the interception of sodium ions in the roots.

[0089] In terms of the potassium-sodium ratio, all MOP treatments significantly increased the leaf potassium-sodium ratio (p < 0.05), with the 0.5 g / L treatment reaching 7.460 ± 0.794, an increase of about 44.5%. The root potassium-sodium ratio was significantly reduced under the 0.1, 0.2, and 0.5 g / L treatments (p < 0.05), indicating that MOP treatment effectively optimized plant ion balance and enhanced salt tolerance by promoting potassium ion transport to the leaves and limiting sodium ion transport to the aboveground parts.

[0090] The results of the experiments showed that the rhizosphere irrigation treatment of MOP had a clear concentration-dependent effect on the growth promotion and stress resistance regulation of maize seedlings under salt stress. The optimal concentration was 0.2 g / L, which showed the best or better effects in promoting biomass accumulation, reducing oxidative stress damage, enhancing antioxidant defense capacity, improving photosynthetic capacity, optimizing water metabolism, and improving ion balance. This concentration significantly increased the soil potassium-sodium ratio (an increase of 17.7%) and optimized the plant ion distribution strategy: the leaf potassium content increased significantly by about 34.2%, the leaf potassium-sodium ratio increased significantly by about 24.4%, and the root potassium-sodium ratio decreased significantly by about 28.2%. This indicated that MOP effectively maintained plant ion balance and enhanced the salt tolerance of maize seedlings by promoting potassium ion transport to the aboveground parts and limiting sodium ion transport to the leaves. The 0.1 g / L treatment had a second-best effect, while the 0.5 g / L high-concentration treatment significantly increased the leaf potassium content (an increase of 102.5%) and the potassium-sodium ratio, but showed inhibitory effects on key growth indicators such as biomass and SPAD value, indicating that excessive concentration may lead to ion imbalance. This study provides important concentration reference for the practical application of MOP in maize cultivation in saline-alkali soils from the perspectives of physiology, biochemistry, and soil-plant ion synergistic regulation.

[0091] Natural plant extracts, as a widely available, green, and pollution-free natural substance, have significant ecological advantages. They are safe for humans and animals and do not burden the ecological environment. Their application method is simple and cost-effective, and they can effectively enhance the stress resistance of maize under salt stress, have important agricultural application value and broad prospects for popularization, and are an ideal choice for addressing the challenges of planting in saline-alkali soils.

[0092] While the application has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various modifications or changes can be made therein without departing from the spirit and scope thereof. Accordingly, it is intended that all such modifications and changes be included within the scope of the application as claimed.

Claims

1. A method of enhancing salt tolerance in maize, comprising, The application relates to a natural plant extract preparation for rhizosphere irrigation, and belongs to the technical field of plant protection. The active ingredient of the natural plant extract preparation is moringa polysaccharide. The natural plant extract preparation is an aqueous solution, and the concentration of the moringa polysaccharide is 0.05-1.0 g / L.

2. The method of claim 1, wherein, The rhizosphere irrigation is carried out at a frequency of once every 2-4 days, and the irrigation is continuously carried out for 2-4 times.

3. The method of claim 1, wherein, The rhizosphere irrigation is started about 7 days after the corn seedlings grow to the stage of 2-4 true leaves.

4. The method of claim 3, wherein, The dosage form of the natural plant extract preparation is one of the following: water agent, powder, granule, water dispersible granule, suspension, microemulsion, emulsifiable concentrate, concentrated solution and slow-release agent.

5. The method of claim 1, wherein, The corn is planted in saline-alkali soil.

6. The method of claim 1, wherein, The saline-alkali soil has the following physicochemical indexes: the EC value is 1.0-4.0 mS / cm, and the pH value is 7.5-8.

5.

7. The method of claim 6, wherein, The application comprises the following components: active ingredient and auxiliary materials.

8. A natural plant extract formulation for improving salt tolerance in maize, characterized in that, The active ingredient is moringa polysaccharide.

9. The natural plant extract preparation according to claim 8, characterized in that, The moringa polysaccharide is a natural polysaccharide extracted from the leaves of a moringa tree. The concentration of the moringa polysaccharide in the natural plant extract preparation is 0.05 g / L-1.0 g / L.

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