Drought-resistant growth-promoting soil-planting composite substrate suitable for dry-hot valley, and preparation method and application thereof

Abstract

The application discloses a kind of drought-resistant growth solid soil-plant complex matrix suitable for dry-hot valley and its preparation method and application, belong to ecological restoration matrix technical field.The composite matrix includes mature sludge nutrient soil, microencapsulated bacterial agent, overburned magnesium oxide-potassium dihydrogen phosphate compound, composite buffer component, water-retaining-salt-resistant component, tea polyphenol-phytic acid compound.Microencapsulated bacterial agent uses heat-resistant domesticated bacillus subtilis and drought-resistant domesticated mucorales as core, proline as osmotic protectant, calcium alginate as inner shell, chitosan quaternary ammonium salt as outer shell;Composite buffer component includes PHA-coated citric acid particles and the like;Water-retaining-salt-resistant component is obtained by compounding water-retaining agent and modified attapulgite.The composite matrix realizes mechanical consolidation and microbial activity compatibility, water-retaining drought resistance and salt regulation coordination, organic solid waste resource utilization and effective control of secondary fermentation risk through the synergistic cooperation of six components, adapts to dry-hot valley environment.

Description

Technical Field

[0001] This invention belongs to the field of ecological restoration substrate technology, specifically a drought-resistant, growth-promoting, soil-stabilizing, and vegetation-growth composite substrate suitable for hot and dry valleys, its preparation method, and its application. Background Technology

[0002] The arid and hot valley region experiences consistently high temperatures and low rainfall, with evaporation far exceeding precipitation. Rainfall is unevenly distributed in time and space, and severe seasonal droughts are frequent. Coupled with factors such as foehn winds, steep slope instability, and short-duration torrential rain erosion, slopes simultaneously face triple erosion from drought, torrential runoff, and strong winds. These extremely harsh site conditions place extremely high demands on the consolidation strength, water retention and drought resistance, long-term nutrient supply, and microbial survival stability of the vegetation substrate. If the substrate cannot adapt to the regional stress environment, problems such as substrate loss, water depletion, poor vegetation emergence, and premature fading of restoration effects can easily occur, significantly increasing the cost of ecological restoration materials and subsequent maintenance. Furthermore, preparing harmless organic solid waste as a slope restoration substrate can not only solve the solid waste disposal problem but also improve the shortcomings of the region's native soil, which is lacking in organic matter and nutrients. Therefore, developing a multifunctional vegetation substrate based on organic solid waste is a core technical approach for the ecological restoration of steep slopes in arid and hot valleys.

[0003] However, due to the unique site conditions of hot and dry valleys, including strong evaporation, intense wet and dry cycles, combined water and wind erosion, and the harsh physical and chemical properties of the native soil, traditional hydroseeding technology and ordinary improved vegetation substrates are difficult to adapt to the site conditions. In practical applications, the following four technical challenges are encountered: Firstly, the region experiences a dry season lasting 6-7 months, during which there is almost no effective rainfall to replenish soil moisture. Extreme maximum temperatures on bare soil slopes and substrate surfaces can reach 55-65℃. Conventional single-type water-retaining agents rapidly degrade their water-locking performance under high temperatures. Organic matter within the substrate undergoes rapid mineralization and decomposition under high-temperature stress, compounded by the continuous strong transpiration from foehn winds, easily leading to the drought and death of seedlings on the slope surface. Simultaneously, long-term soil evaporation causes salts within the substrate to migrate upwards along capillary pores, eventually accumulating in large quantities on the substrate surface, forming salt infiltration stress. The combined effects of soil drought and salt stress inhibit normal seedling survival, and existing commercially available plant substrates generally lack targeted salt regulation functions. Secondly, conventional exogenous growth-promoting bacteria are not immobilized and protected using porous carriers, making them highly susceptible to rapid inactivation under the harsh conditions of high temperature and drought in the region. Furthermore, general-purpose microbial strains have poor compatibility with local drought-resistant shrub and grass species, resulting in very limited actual effects of the strains in promoting root growth and enhancing plant resistance.

[0004] Secondly, arid red soil is widely distributed in the hot and dry valleys. This type of soil exhibits typical swelling and shrinkage characteristics: it expands dramatically when it absorbs water, and shrinks and cracks severely when it dries. This repeated cycle leads to the destruction of the internal cementation structure of the substrate and the continuous development of microcracks. Conventional vegetation substrates are not designed with buffer pore structures adapted to soil swelling and shrinkage. Under the repeated wet and dry cycles in the region, the structural integrity of the substrate continuously deteriorates. During the rainy season, short-term heavy rainfall and runoff directly erode the substrate, causing sediment loss. During the dry season, continuous strong winds erode the fine particles on the surface of the substrate, causing dust loss.

[0005] Third, ordinary vegetation substrates without added inorganic consolidation components have low cohesion. When applied to steep slopes, they are prone to collapse due to concentrated heavy rain, and the stability of the slope structure cannot be guaranteed. Although increasing the amount of consolidation material can significantly enhance the overall mechanical strength of the substrate, commonly used consolidation cementitious materials such as cement continuously release alkaline substances during hydration, causing a sharp increase in pH value in the early stage. Furthermore, due to the scarcity of rainfall and weak leaching in dry and hot valleys, the alkalinity of the substrate remains high for a long time. Excessively high pH value of the substrate can kill functional microbial communities and burn the delicate roots of seedlings.

[0006] Fourth, uncomposted organic solid waste contains a large amount of unstable and easily degradable organic matter. After the substrate is sprayed onto the slope, the external water supply will meet the metabolic conditions of microorganisms, activating their vigorous aerobic respiration and metabolism. This leads to secondary fermentation inside the substrate and a sharp increase in local temperature, directly scorching the newly formed radicles and early seedlings. At the same time, the massive proliferation of microorganisms will produce a significant nitrogen biological fixation effect. Microorganisms compete for readily available nitrogen nutrients in the substrate, resulting in nitrogen deficiency in seedlings, leading to yellowing, stunted growth, and even death.

[0007] Based on this, the development of a multifunctional vegetation substrate that can simultaneously achieve water retention and drought resistance, salt regulation, resistance to expansion and contraction erosion from wet and dry cycles, consolidation on steep slopes and compatibility with microorganisms, long-term slow release of nutrients, and inhibition of secondary fermentation has significant engineering application value and ecological scientific significance. Summary of the Invention

[0008] The purpose of this invention is to provide a drought-resistant, soil-stabilizing, and plant-based composite substrate suitable for hot and dry valleys, as well as its preparation method and application, to effectively solve the problems of poor water retention and drought resistance, insufficient compatibility between soil stabilization and slope protection and microorganisms, easy nutrient loss, and low survival rate of microbial agents in existing ordinary improved plant substrates under extreme hydrothermal conditions in hot and dry valleys.

[0009] The objective of this invention is achieved through the following technical solution: A drought-resistant, soil-stabilizing, and vegetation-supporting composite substrate suitable for hot and dry valleys comprises the following components by weight: 100 parts of well-rotted sludge nutrient soil, 3-8 parts of microencapsulated bacterial agent, 1.5-4 parts of overburned magnesium oxide-potassium dihydrogen phosphate compound, 0.8-2 parts of composite buffer component, 0.4-1.5 parts of water-retaining and salt-inhibiting component, and 0.3-0.6 parts of tea polyphenol-phytic acid compound; wherein: The composted sludge nutrient soil is a product of deep composting of sludge from urban sewage treatment plants through aerobic composting, with a seed germination index GI≥80% and electrical conductivity EC≤3mS / cm. The microencapsulated bacterial agent is a double-shell core-shell particle with a mixture of compound growth-promoting bacteria and proline as the core, and sequentially coated with a calcium alginate layer and a chitosan quaternary ammonium salt layer. The compound growth-promoting bacteria consist of heat-resistant Bacillus subtilis and drought-resistant Tuberculosus mosieuria. The Bacillus subtilis underwent heat acclimation treatment, which included: subjecting Bacillus subtilis to multiple rounds of high-temperature directional screening, so that the acclimated Bacillus subtilis, under culture conditions of 50~60℃, had an OD600 value ≥1.0 in the fermentation broth and a spore formation rate ≥85%. The *Morchella mosierifolia* underwent drought acclimation treatment, which included: under low water stress conditions, using host plants to conduct multiple rounds of live symbiotic subculture screening of *Morchella mosierifolia*, so that the acclimated *Morchella mosierifolia* had a significantly higher mycorrhizal colonization rate on the host roots than before acclimation when the substrate moisture content was 30-60% of field capacity.

[0010] The composite buffer component is composed of calcium humate, diatomaceous earth, calcium carbonate, and PHA-coated citric acid particles. The water-retaining and salt-inhibiting component is a compound of potassium polyacrylate water-retaining agent and modified attapulgite clay; The modified attapulgite is obtained by modifying attapulgite with chitosan quaternary ammonium salt; The overburned magnesium oxide is low-activity magnesium oxide obtained by calcining magnesite at a high temperature of 1550~1650℃.

[0011] Preferably, the preparation method of the microencapsulated bacterial agent is as follows: Bacillus subtilis, after being acclimated to a heat-resistant state, is fermented and cultured to the logarithmic growth phase. Proline is added to a final concentration of 5-15 mmol / L, followed by the addition of drought-resistant *Dendrobium mossioides* agent, and the mixture is stirred until homogeneous. The mixture is then mixed with a 2-4 wt% sodium alginate solution and added dropwise to a 3-5 wt% calcium chloride solution for cross-linking for 15-30 minutes, forming a single-layer microcapsule with a core of compound growth-promoting bacteria and proline, and a shell of calcium alginate. After washing with deionized water, the microcapsule is immersed in a 0.1-0.3 wt% chitosan quaternary ammonium salt solution for secondary coating, forming an outer chitosan quaternary ammonium salt layer. The microencapsulated bacterial agent is then vacuum-dried until the moisture content is ≤15%. In this method, the calcium alginate layer provides mechanical protection and Mg... 2+The chitosan quaternary ammonium salt layer provides a function to delay the diffusion of proline, and the two layers work together to enhance the survival ability of the bacterial agent in high temperature and drought environment.

[0012] Preferably, in the overburned magnesium oxide-potassium dihydrogen phosphate compound, the molar ratio of overburned magnesium oxide to potassium dihydrogen phosphate is 2~4:1.

[0013] Preferably, in the composite buffer component, the mass ratio of calcium humate, diatomaceous earth, calcium carbonate and PHA-coated citric acid particles is 1:3~5:0.1~0.3:0.5~1; the PHA-coated citric acid particles have a citric acid content of 40~60wt%, a polyhydroxyalkanoate weight-average molecular weight of 50000~150000Da, and a particle size of 50~200μm.

[0014] Preferably, in the water-retaining and salt-resistant component, the mass ratio of potassium polyacrylate water-retaining agent to modified attapulgite is 1:0.3~0.8; the particle size of the potassium polyacrylate water-retaining agent is 80~120 mesh; and the content of chitosan quaternary ammonium salt in the modified attapulgite is 8~15wt%.

[0015] Preferably, the preparation method of the composted sludge nutrient soil is as follows: dewatered sludge from urban sewage treatment plants is mixed with corn stalk powder at a wet weight ratio of 1:0.3~0.5, the C / N ratio is adjusted to 25~30:1, the moisture content is 55~65%, and the mixture is inoculated with a high-temperature resistant fermentation agent for aerobic composting treatment. The compost temperature is ≥55℃ for a duration of not less than 15 days, and the total composting cycle is not less than 45 days. After sieving, the GI is ≥80% and EC is ≤3mS / cm to obtain the composted sludge nutrient soil.

[0016] Preferably, the method for preparing the modified attapulgite is as follows: Attapulgite is thermally activated at 350-400℃ for 2-3 hours and then cooled to room temperature. The thermally activated attapulgite is mixed with a chitosan quaternary ammonium salt solution at a solid-liquid ratio of 1:8-12 and stirred at 60-70℃ for 4-6 hours. After centrifugation, the mixture is washed with deionized water, dried at 80-90℃ to constant weight, and pulverized through an 80-120 mesh sieve to obtain modified attapulgite.

[0017] Preferably, the method for preparing the PHA-coated citric acid particles is as follows: Citric acid is pulverized to 50-200 μm as the core material; PHA is dissolved in dichloromethane to prepare a 5-10 wt% solution; citric acid particles are dispersed in the PHA solution, and slowly added to a 0.5-1 wt% polyvinyl alcohol aqueous solution with stirring. After emulsification, the organic solvent is removed by vacuum evaporation, and the solution is vacuum dried until the residual solvent content is below the detection limit; the solidified particles are collected by filtration, washed with deionized water, and dried to obtain PHA-coated citric acid particles with a particle size of 50-200 μm. In this method, citric acid is uniformly coated in a PHA matrix, and the PHA gradually degrades in the soil environment, achieving a continuous slow release of citric acid. By controlling the molecular weight of PHA and the thickness of the coating layer, the release rate of citric acid can be adjusted to match the hydration process of the gelation system and the long-term pH stability requirements of the substrate.

[0018] Furthermore, to achieve the above objectives, the present invention also provides a method for preparing a drought-resistant, growth-promoting, soil-stabilizing, and vegetation-based composite substrate. A tea polyphenol-phytic acid compound is premixed with a portion of well-rotted sludge nutrient soil at a mass ratio of 1:8~12, and aged at 25~30℃ for at least 48 hours. This mixture is then stirred with the remaining well-rotted sludge nutrient soil and a composite buffer component to obtain a basic premix. Subsequently, a microencapsulated bacterial agent and a water-retaining and salt-inhibiting component are added, and the mixture is stirred at 25~35℃. Finally, an overburned magnesium oxide-potassium dihydrogen phosphate compound is added and stirred until homogeneous to obtain the final product.

[0019] In the preparation method provided above, the tea polyphenol-phytic acid compound is first mixed with some well-rotted sludge nutrient soil and aged. This allows the polyphenolic hydroxyl groups of tea polyphenols to form an organic complex with the humic acid in the sludge organic matter through hydrogen bonding and hydrophobic interactions, thereby reducing the free state concentration and molecular diffusion rate of tea polyphenols.

[0020] Subsequently, a graded mixing process was adopted to separate the gelling components from other components, avoiding premature contact with moisture and reaction of the gelling components; at the same time, the microencapsulated bacterial agent and organic functional components were mixed with the superburned magnesium oxide-potassium dihydrogen phosphate compound in stages to maximize the protection of the activity of functional bacteria.

[0021] Furthermore, to achieve the above objectives, the present invention also provides the application of drought-resistant, growth-promoting, and soil-stabilizing vegetation substrates in the ecological restoration of steep slopes in dry and hot river valleys.

[0022] Compared with the prior art, the beneficial effects of the present invention are: This invention addresses the technical challenges of high-temperature and high-evaporation conditions, cyclical expansion and contraction between dry and wet conditions, combined water and wind erosion, and secondary fermentation of organic solid waste in arid and hot valleys. It provides a drought-resistant, soil-stabilizing, and vegetation-supporting composite substrate suitable for arid and hot valleys. The functions of each component in this composite substrate are as follows: Well-rotted sludge nutrient soil: provides a stable source of organic matter and nutrients for the substrate, making up for the shortcomings of the original soil in the dry and hot valleys, which is lacking in organic matter and nutrients.

[0023] Microencapsulated bacterial agent: Employing a double-shell core-shell structure, the core consists of heat-acclimated Bacillus subtilis and drought-acclimated Corydalis mosieurica, with proline as a permeation protectant, calcium alginate as the inner shell, and chitosan quaternary ammonium salt as the outer shell. This structure offers several functionalities: First, after heat acclimation, Bacillus subtilis can metabolize normally at 50-60℃, continuously exerting its growth-promoting functions such as phosphorus solubilization and plant growth hormone secretion in the hot, dry valley environment. Second, after subculture acclimation under low water stress, Corydalis mosieurica exhibits significantly enhanced mycorrhizal infection ability against host plants under drought conditions, expanding the effective water absorption range of plant roots. Third, the chitosan quaternary ammonium salt outer shell delays the diffusion of proline out of the microcapsule, prolonging its permeation protection effect on the bacterial cells. This microencapsulation significantly improves the survival rate of the bacterial agent in the high-temperature, drought environment after substrate spraying, solving the problem of rapid inactivation of conventional exogenous bacterial agents under extreme hydrothermal stress.

[0024] Overburned magnesium oxide-potassium dihydrogen phosphate complex: Overburned magnesium oxide reacts with potassium dihydrogen phosphate to form a stable hydrated gel phase of potassium magnesium phosphate dihydrate. During the initial hydration phase, the pH of the system can rise to 8.8-9.2 in a short period. At this point, the citric acid slowly released from the PHA in the composite buffer component chelates Mg in real time. 2+ And neutralize OH - This system maintains a stable pH level of 7.5–8.5 over a long period, thus avoiding the damage to functional microorganisms and seedling roots caused by the strong alkalinity of conventional cement hydration. Simultaneously, the cementitious system exhibits early strength and rapid hardening characteristics, providing excellent early consolidation capacity for steep slope substrates. Its hydration products possess micro-expansion properties, which can partially offset the shrinkage stress generated by the wet-dry cycle of dry red soil in hot, dry valleys, reducing the development of microcracks in the substrate.

[0025] The composite buffer components are as follows: First, PHA-coated citric acid particles partially break due to mechanical shearing during the initial gelation stage, releasing a small amount of citric acid that chelates with overburned magnesium oxide, delaying the setting time of the gelling components and expanding the high-temperature construction operation window. Second, PHA gradually degrades under the action of soil microorganisms, continuously releasing citric acid and maintaining the long-term pH stability of the substrate. Third, the well-developed porous structure of diatomaceous earth can physically adsorb and retain ammonium nitrogen, reducing nitrogen leaching. Fourth, calcium carbonate acts as a pH safety cushion, dissolving and consuming H₂ when the local accumulation of PHA degradation products leads to a decrease in pH. + It maintains the stability of the acid and alkaline environment of the substrate; at the same time, the citric acid released by the PHA-coated citric acid particles reacts with the calcium ions in the substrate to generate calcium citrate, which can fill the micropores and microcracks of the substrate and improve the bonding strength of the crack surface to a certain extent.

[0026] Water-retaining and salt-inhibiting components: The water-retaining agent extends the effective water supply cycle of vegetation under drought conditions through repeated water absorption and release cycles; the modified attapulgite soil fills the capillary channels of the substrate through its micro-nano pore structure, increasing the resistance to upward water migration. Together with the water-retaining agent, it synergistically reduces the rate of water loss driven by evaporation, alleviating water stress under strong evaporation conditions in hot and dry valleys.

[0027] Tea polyphenol-phytic acid compound: Tea polyphenols inhibit the activity of microbial proteases through phenolic hydroxyl groups, while phytic acid inhibits the activity of metalloproteinases by chelating metal ions. The two work together to block the aerobic metabolic pathways of miscellaneous bacteria in organic solid waste, preventing secondary fermentation heat damage and nitrogen biological fixation caused by the first water replenishment after substrate spraying.

[0028] There is a synergistic relationship among the above six components: PHA-coated citric acid particles delay flash coagulation in the early stage of gelation through the immediate release of a small amount of citric acid; in the middle and late stages of gelation, PHA degradation continuously releases acid to maintain pH stability; simultaneously, citric acid forms a weak calcium citrate gel with calcium ions in the substrate, reducing the surface moisture evaporation rate and indirectly slowing down the migration and concentration of proline to the surface; PHA degradation products serve as a carbon source for microorganisms, promoting the colonization activity of the microencapsulated bacterial agent after release; based on this, the hydration process of the overburned magnesium oxide-potassium dihydrogen phosphate compound and the formation of the shell structure of the bacterial agent microcapsules are synchronized: the high ionic strength environment in the early stage of the gelation reaction delays flash coagulation. The slow swelling rate of the outer shell keeps the microbial agent embedded during the intense gelation stage. Once gelation is nearing completion and hydration products stabilize, the shell gradually swells, releasing the microbial agent after the substrate's chemical environment has stabilized, achieving a temporal match between agent release and the gelation process. Simultaneously, the tea polyphenol-phytic acid complex, through pre-aging with partially decomposed sludge nutrient soil, forms hydrogen-bonded complexes between tea polyphenols and humic acid, reducing their free-state concentration and diffusion rate. While retaining its inhibitory effect on microbial fermentation, this reduces non-target contact of tea polyphenols with *Tetranychus mosieboldii* spores, effectively mitigating the conflict between fermentation inhibition and growth-promoting fungal functions. These three factors synergistically ensure the comprehensive performance of the substrate in the extreme environment of a dry-hot valley from three dimensions: ease of construction, protection of microbial agent activity, and functional compatibility.

[0029] In summary, this invention achieves compatibility between mechanical consolidation of the substrate and microbial activity, synergy between water retention and drought resistance and salt regulation, and effective control of the risks of secondary fermentation and resource utilization of organic solid waste through the synergistic combination of six components. It is suitable for extreme site conditions such as high temperature, strong evaporation, drought, barrenness, and steep slopes in hot and dry valleys. Detailed Implementation

[0030] Example 1 I. Raw material preparation: (1) Preparation of composted sludge nutrient soil: Dewatered sludge (moisture content of about 80%) from urban sewage treatment plants was mixed with corn straw powder (passed through a 20-mesh sieve) at a wet weight ratio of 1:0.4, and the C / N ratio was adjusted to 28:1 with a moisture content of 60%. The mixture was then inoculated with a high-temperature resistant fermentation agent (the high-temperature resistant fermentation agent was a commercially available compound thermophilic bacteria for garden composting, with an effective viable count ≥2.0 × 10⁻⁶ on a dry basis). 9 The compost, containing CFU / g of *Bacillus stearothermophilus*, *Actinomyces thermophilus*, and *White rot fungi* in a 1:1:1 ratio of viable bacteria (added at 0.2% of the total mass of the mixture), is subjected to aerobic composting. The compost pile is 1.5m high, turned every 5 days, and maintained at ≥55℃ for 18 days, with a total composting cycle of 50 days. After composting, large, uncomposted particles are removed by sieving (passing through a 5mm sieve). Seed germination index (GI) is 87%, organic matter content is 28%, moisture content is 28%, pH is 7.2, and electrical conductivity (EC) is 2.1 mS / cm, yielding the matured sludge nutrient soil. Heavy metal content (As, Pb, Cd, Cr, Hg) and pathogen indicators (fecal coliforms, Ascaris egg mortality rate) all meet the requirements of the standard "Sludge Quality for Landscaping and Disposal of Sludge from Urban Wastewater Treatment Plants".

[0031] (2) Preparation of microencapsulated bacterial agents: ① Heat acclimation of Bacillus subtilis: Commercially available lyophilized Bacillus subtilis powder was inoculated into LB liquid medium at a rate of 0.3 g / 100 mL and cultured at 37℃ and 180 rpm for 20 h with shaking to activate the bacteria until OD600 = 1.2. The activated bacterial culture was then transferred to fresh LB liquid medium at a 5% inoculum rate, with an initial culture temperature of 37℃. Every 24 h, the culture was transferred to fresh medium at a 5% inoculum rate, increasing the temperature by 2℃ every three transfers, gradually raising the temperature to 55℃. The culture was then stably passaged at 55℃ for 6 generations (transferring once every 24 h). After the culture was completed, heat-resistant strains with OD600 = 1.1 at 55℃ were screened, with a generation time of 52 min and a spore formation rate of 85%. These were considered heat-acclimated Bacillus subtilis strains and stored at 4℃ on slant culture for later use. The domesticated strains can metabolize stably at 60℃ for a long time and can withstand short-term high-temperature shocks of 65℃, which is compatible with the diurnal temperature difference and extreme high-temperature fluctuations in the dry-hot valley.

[0032] ② Drought tolerance acclimatization of *Tetranychus mosierifolius*: The acclimatization substrate was peat moss: river sand = 2:1 (volume ratio). The culture conditions were 25±2℃, 3000 lux, 16h light / 8h darkness, and 60%~70% humidity. The original *Tetranychus mosierifolius* inoculum (commercially available, spore density approximately 30 spores / g) was inoculated into the rhizosphere of 30-day-old *Rhizomys purpurea* seedlings (10g inoculum per pot). Under normal water supply conditions (substrate moisture content of 70% of field capacity), the mycorrhizal root segments and rhizosphere substrate were harvested, and the spore density was measured to be 55 spores / g. New *Rhizoma Sinensis* seedlings were re-inoculated with activated spores. Subculturing was carried out under low water stress conditions (45% of field capacity) with a substrate moisture content of 125%. Harvesting was conducted every 8 weeks, with four consecutive subculturing cycles, ultimately yielding a drought-tolerant acclimatization inoculant with a spore density of 58 spores / g. This inoculant was stored at 4℃ for later use. The low-moisture environment inhibits massive spore proliferation; the purpose of acclimatization is to enhance the drought-tolerant activity of the spores, not to increase the total spore count.

[0033] ③ Inoculate heat-tolerant Bacillus subtilis at a 5% inoculum size into 500 mL of LB liquid medium and ferment at 37°C and 180 rpm until OD600 = 1.5. Continue culturing for 12-24 h to induce spore formation. Microscopic examination confirms a spore formation rate of 85%. Subsequently, centrifuge at 8000 rpm and 4°C for 10 min, collect the bacterial cells, and resuspend them in sterile physiological saline to a bacterial concentration of 2 × 10⁻⁶. 8 CFU / mL. Add proline to a final concentration of 10 mmol / L and stir well. Then add drought-resistant and domesticated Bacillus subtilis fungicide (added at a mass ratio of 1:1 between Bacillus subtilis bacterial solution and Bacillus subtilis fungicide), stir well, and obtain a compound bacterial solution.

[0034] ④ Dissolve sodium alginate in deionized water to prepare a 3wt% sodium alginate solution, sterilize at 121℃ for 15 min, and cool to room temperature. Mix the compound bacterial solution with the 3wt% sodium alginate solution at a volume ratio of 1:1. Add the mixture dropwise to 500mL of 4wt% calcium chloride solution using a syringe, and cross-link for 20 min to form a single-layer microcapsule with compound growth-promoting bacteria and proline as the core and calcium alginate as the shell. Wash three times with deionized water, immerse in 200mL of 0.2wt% chitosan quaternary ammonium salt (90% substitution degree) solution for 8 min for a second coating, and then vacuum dry at 38℃ and -0.09MPa until the moisture content is 12% to obtain the microencapsulated bacterial agent. The microcapsules had a particle size of 0.8–1.5 mm, a final proline concentration of 10 mmol / L, and a chitosan quaternary ammonium salt layer thickness of approximately 12 μm. Plate counting analysis showed that the bacterial survival rate after microencapsulation was 82%, and the AMF (arbuscular mycorrhizal fungi) spore germination rate was 78% of the germination rate before drying. After sealing, the microcapsules were stored at 4°C for later use. After step blue staining, the outer chitosan quaternary ammonium salt layer appeared light blue (contrasting with the colorless inner calcium alginate layer), and the interface between the two shell layers was clearly distinguishable.

[0035] (3) Preparation of water-retaining and salt-inhibiting components: ① The raw attapulgite ore (passed through a 200-mesh sieve) was placed in a muffle furnace and thermally activated at 380℃ for 2.5 hours, then cooled to room temperature. The thermally activated attapulgite was mixed with a 3wt% chitosan quaternary ammonium salt (substitution degree 90%) solution at a solid-liquid ratio of 1:10 (g:ml), and stirred at 65℃ for 5 hours. After centrifugation (4000rpm, 10min), the mixture was washed three times with deionized water, dried at 85℃ to constant weight, and pulverized through a 100-mesh sieve to obtain modified attapulgite with a chitosan quaternary ammonium salt content of 12wt%.

[0036] The chitosan quaternary ammonium salt content in modified attapulgite was determined by thermogravimetric analysis (TGA). The specific test conditions were as follows: 5–10 mg of sample was accurately weighed and placed in an alumina crucible. Under a nitrogen atmosphere (flow rate 50 mL / min), the temperature was increased from room temperature (25 °C) to 800 °C at a rate of 10 °C / min. The chitosan quaternary ammonium salt content was calculated based on the percentage of weight loss in the temperature range of 300 °C to 600 °C. 1 g of each sample, before and after modification, was added to 50 mL of deionized water and ultrasonically dispersed for 5 min. The zeta potential of the suspension was then measured using a zeta potential meter. The zeta potential of unmodified attapulgite was -25 to -35 mV, while that of modified attapulgite was +15 to +25 mV, indicating successful grafting of the quaternary ammonium salt.

[0037] ② Add the above modified attapulgite clay and potassium polyacrylate water-retaining agent (particle size 80~120 mesh, water absorption ratio in deionized water 400g / g) into a mixer at a mass ratio of 0.5:1, and stir at 80rpm for 15min at room temperature until uniform to obtain the water-retaining and salt-resistant component.

[0038] (4) Preparation of the composite buffer component: ① Citrate (food grade) pulverizes and sieves to a size of 100-150 μm to use as the core material. Dissolve polyhydroxyalkanoates (PHA, weight average molecular weight 100,000 Da) in dichloromethane to prepare an 8 wt% solution. Disperse the citric acid particles in the PHA solution (citric acid to PHA mass ratio 1:1), and slowly add an equal volume of 0.8 wt% polyvinyl alcohol (88% degree of alcoholysis, weight average molecular weight 100,000) aqueous solution while stirring. Emulsify at 8000 rpm for 5 min in a homogenizer, remove dichloromethane by vacuum evaporation at 40℃, and then vacuum dry at 40℃ (vacuum degree -0.095 MPa) until the solvent residue is below the detection limit (gas chromatography detection of dichloromethane residue <1 ppm). Filter and collect the solidified particles, wash three times with deionized water, and dry at 45℃ to constant weight to obtain PHA-coated citric acid particles. The citric acid content is 50 wt%, and the particle size is 100-180 μm. The degradation half-life of the PHA coating is greater than 180 days at 30°C and 60% relative humidity, and greater than 30 days at 55°C.

[0039] ② Add calcium humate (humic acid content ≥60%), diatomaceous earth (food grade, passed through a 200-mesh sieve), calcium carbonate (light calcium carbonate, passed through a 300-mesh sieve) and the above-mentioned PHA-coated citric acid particles into a mixer at a mass ratio of 1:4:0.2:0.8, and stir at 60 rpm for 20 minutes at room temperature until uniform to obtain the composite buffer component.

[0040] (5) Preparation of overburned magnesium oxide-potassium dihydrogen phosphate compound: Magnesite raw material was calcined at 1600℃ for 3h to obtain overburned magnesium oxide (MgO content ≥93%). The activity of overburned magnesium oxide was determined by citric acid neutralization method. 2.0g of overburned magnesium oxide sample was accurately weighed and added to 100mL of 1mol / L citric acid solution, and 3-5 drops of phenolphthalein indicator were added. Under constant temperature stirring at 25℃, the time required for the solution to change from colorless to pink was recorded with a stopwatch. In this example, the neutralization time was measured to be 140 seconds (indicating that the MgO activity is moderate, corresponding to an initial setting time of about 20-30min for magnesium potassium phosphate cement). Overburned magnesium oxide and potassium dihydrogen phosphate (passed through a 200-mesh sieve) were added to a mixer at a molar ratio of 3:1 and mixed thoroughly for 20min under dry conditions at room temperature to obtain the overburned magnesium oxide-potassium dihydrogen phosphate compound, which was then sealed and stored in a moisture-proof container.

[0041] (6) Preparation of tea polyphenol-phytic acid compound: Mix tea polyphenol (purity ≥ 98%) with 70wt% phytic acid aqueous solution at a mass ratio of 1:1 (the mass of phytic acid is calculated based on the mass of the aqueous solution), stir at room temperature for 10 minutes until uniform, and the tea polyphenol-phytic acid compound is obtained.

[0042] II. Preparation of drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate.

[0043] (1) Pre-aging step: Take 5% (5 parts) of the total amount of composted sludge nutrient soil, mix tea polyphenol-phytic acid compound (0.5 parts) with this part of composted sludge nutrient soil, and age it at 30℃ for 50h to obtain pre-aged fermentation inhibited sludge material.

[0044] (2) Graded mixing step: Take 3 parts of the overburned magnesium oxide-potassium dihydrogen phosphate compound as a premix for use as a gelling premix. Add the remaining composted sludge nutrient soil (95 parts), the above-mentioned pre-aged fermentation inhibiting sludge material and composite buffer component (1.5 parts) into a mixer and stir at 80 rpm for 15 min to obtain the basic premix. Add the microencapsulated bacterial agent (5 parts) and water-retaining-salt-inhibiting component (1 part) to the basic premix and stir slowly at 50 rpm for 12 min at 30℃. Finally, add the gelling premix and continue to stir at 50 rpm for 8 min until uniform, thus obtaining the drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate. The finished product has a moisture content of 22% and a pH value of 7.6. After sealing and packaging, store at room temperature away from light.

[0045] Example 2 This embodiment adjusts some parameters based on Embodiment 1, as follows: (1) In the preparation of nutrient soil for decomposed sludge, the wet weight ratio of sludge to corn straw powder is 1:0.3, the C / N ratio is 25:1, the moisture content is 55%, the pile temperature is ≥55℃ for 15 days, the total cycle is 45 days, GI=82%, and EC=2.8mS / cm.

[0046] (2) The final concentration of proline in the microencapsulated bacterial agent is 5 mmol / L, the concentration of sodium alginate is 2 wt%, the concentration of calcium chloride is 3 wt%, the cross-linking time is 15 min, the concentration of chitosan quaternary ammonium salt is 0.1 wt%, the soaking time is 5 min, and the drying temperature is 35℃.

[0047] (3) The molar ratio of the overburned magnesium oxide-potassium dihydrogen phosphate compound is 2:1.

[0048] (4) The mass ratio of calcium humate, diatomaceous earth, calcium carbonate and PHA-coated citric acid particles in the composite buffer component is 1:3:0.1:0.5.

[0049] The mass ratio of modified attapulgite to water-retaining agent in the water-retaining and salt-blocking component is 0.3:1.

[0050] (5) Amounts of each component in the preparation of the composite matrix: 3 parts microencapsulated bacterial agent, 1.5 parts overburned magnesium oxide-potassium dihydrogen phosphate compound, 0.8 parts composite buffer component, 0.4 parts water-retaining-salt-inhibiting component, and 0.3 parts tea polyphenol-phytic acid compound. In the pre-aging step, 3 parts of well-rotted sludge nutrient soil (calculated as 10 times the amount of 0.3 parts of tea polyphenol-phytic acid compound) were taken, and the tea polyphenol-phytic acid compound was mixed with the 3 parts of well-rotted sludge nutrient soil. The aging conditions were the same as in Example 1 to obtain pre-aged fermentation-inhibiting sludge material. In the graded mixing step, the remaining well-rotted sludge nutrient soil was 97 parts.

[0051] The remaining steps and parameters are the same as in Example 1.

[0052] Example 3 This embodiment adjusts some parameters based on Embodiment 1, as follows: (1) In the preparation of nutrient soil for decomposed sludge, the wet weight ratio of sludge to corn straw powder is 1:0.5, the C / N ratio is 30:1, the moisture content is 65%, the pile temperature is ≥55℃ for 20 days, the total cycle is 52 days, GI=90%, and EC=2.5mS / cm.

[0053] (2) The final concentration of proline in the microencapsulated bacterial agent is 15 mmol / L, the concentration of sodium alginate is 4 wt%, the concentration of calcium chloride is 5 wt%, the cross-linking time is 30 min, the concentration of chitosan quaternary ammonium salt is 0.3 wt%, the soaking time is 10 min, and the drying temperature is 40℃.

[0054] (3) The molar ratio of the overburned magnesium oxide-potassium dihydrogen phosphate compound is 4:1.

[0055] (4) The mass ratio of calcium humate, diatomaceous earth, calcium carbonate and PHA-coated citric acid particles in the composite buffer component is 1:5:0.3:1.

[0056] (5) The mass ratio of modified attapulgite to water-retaining agent in the water-retaining and salt-resistant component is 0.8:1.

[0057] (6) Amounts of each component in the preparation of the composite matrix: 8 parts microencapsulated bacterial agent, 4 parts overburned magnesium oxide-potassium dihydrogen phosphate compound, 2 parts composite buffer component, 1.5 parts water-retaining and salt-inhibiting component, and 0.6 parts tea polyphenol-phytic acid compound. In the pre-aging step, 6 parts of well-rotted sludge nutrient soil (calculated as 10 times the amount of 0.6 parts of tea polyphenol-phytic acid compound) were taken, and the tea polyphenol-phytic acid compound was mixed with the 6 parts of well-rotted sludge nutrient soil. The aging conditions were the same as in Example 1 to obtain pre-aged fermentation-inhibiting sludge material. In the graded mixing step, the remaining well-rotted sludge nutrient soil was 94 parts.

[0058] The remaining steps and parameters are the same as in Example 1.

[0059] Comparative Example 1 Based on Example 1, the tea polyphenol-phytic acid complex was not added, and the pre-aging step was omitted. The remaining components and preparation steps were the same as in Example 1.

[0060] Comparative Example 2 Comparative Example 2a: Based on Example 1, the microencapsulated bacterial agent contained only heat-acclimated Bacillus subtilis, without the addition of *Bacillus mosierifolius*. The remaining components and preparation steps were the same as in Example 1.

[0061] Comparative Example 2b: Based on Example 1, the microencapsulated bacterial agent contained only drought-tolerant and acclimatized *Bacillus mosierifolius*, without the addition of heat-tolerant and acclimatized *Bacillus subtilis*. The remaining components and preparation steps were the same as in Example 1.

[0062] Comparative Example 3 Based on Example 1, diatomaceous earth was not added to the composite buffer component; instead, calcium humate, calcium carbonate, and PHA-coated citric acid particles were mixed in a mass ratio of 1:0.2:0.8, and the amount of the composite buffer component added to the substrate remained 1.5 parts. The remaining components and preparation steps were the same as in Example 1. Comparative Example 4 Based on Example 1, the overburned magnesium oxide-potassium dihydrogen phosphate compound was replaced with an equal mass of ordinary silicate cement (PO 42.5), without changing the dosage. The remaining components and preparation steps were the same as in Example 1.

[0063] Comparative Example 5 Based on Example 1, the water-retaining and salt-barrier component was replaced with an equal mass of modified attapulgite. The remaining components and preparation steps were the same as in Example 1.

[0064] Comparative Example 6 Based on Example 1, Bacillus subtilis was fermented directly using the original strain without heat acclimation; and *Tetranychus mosierifolius* was fermented directly using the original inoculum without drought acclimation. The remaining components and preparation steps were the same as in Example 1.

[0065] Comparative Example 7 Based on Example 1, the tea polyphenol-phytic acid compound was not pre-aged and was directly mixed with all the composted sludge nutrient soil (i.e., 100 parts) and the composite buffer component. The remaining components and preparation steps were the same as in Example 1.

[0066] Comparative Example 8 The PHA-coated citric acid particles in the composite buffer component were replaced with uncoated citric acid particles of equal mass (even if the effective citric acid content was the same as in Example 1). The remaining components and preparation steps were the same as in Example 1. Comparative Example 9 Based on Example 1, the secondary coating step with chitosan quaternary ammonium salt was omitted in the preparation of the microencapsulated bacterial agent; that is, only microcapsules with a single layer of calcium alginate were prepared without immersion in the chitosan quaternary ammonium salt solution. The remaining components and preparation steps are the same as in Example 1.

[0067] Comparative Example 10 Based on Example 1, instead of preparing microencapsulated bacterial agents, an equal volume of free composite growth-promoting bacterial solution was used (the bacterial solution concentration and strain composition were the same as the composite bacterial solution before microencapsulation in Example 1, with a final proline concentration of 10 mmol / L). This solution was added together with the water-retaining and salt-barrier components during the substrate fractionation mixing step, without the sodium alginate and calcium chloride crosslinking step, and without the addition of sodium alginate, calcium chloride, and chitosan quaternary ammonium salt. The remaining components and preparation steps were the same as in Example 1.

[0068] Comparative Example 11 Based on Example 1, the modified attapulgite in the water-retaining and salt-barrier component was replaced with an equal mass of unmodified attapulgite (only thermally activated at 380°C, without chitosan quaternary ammonium salt modification). The remaining components and preparation steps were the same as in Example 1.

[0069] Comparative Example 12 Based on Example 1, proline was not added in the preparation of the microencapsulated bacterial agent. The remaining components and preparation steps were the same as in Example 1.

[0070] Experimental Example All experiments were performed in triplicate, and the average value of the results was taken. The relative standard deviation (RSD) of each test index should be ≤5%.

[0071] Experimental Example 1: Comprehensive test of substrate mechanical properties, corrosion resistance, water retention and drought resistance, salinity control and long-term durability (results are shown in Tables 1 and 2). 1.1 Mechanical Property Testing of Substrates: The consolidation strength and mechanical properties of the substrates were determined using an unconsolidated undrained quick-shear test system. The composite matrices obtained in Examples 1-3, Comparative Examples 3, 4, 8, and 11 were each added to water to a moisture content of 22%, stirred thoroughly, and then placed into a ring sample mold with a diameter of 61.8 mm and a height of 20 mm. The matrices were cured for 7 days at a temperature of 25±2℃ and a relative humidity of 60±5%. After curing, the cohesion c was measured under standard test conditions (shear rate 0.8 mm / min). Simultaneously, the substrates cured for 7 days were taken, and deionized water was added at a soil-to-water ratio of 1:5. The mixture was shaken and extracted for 30 minutes, and the pH value of the extract was measured using a pH meter.

[0072] 1.2 Dry-wet cycle durability test: The substrate specimens cured for 7 days were subjected to dry-wet cycle treatment: drying in a 55±2℃ forced-air drying oven for 12 hours, followed by immersion in deionized water at 25±2℃ for 12 hours constituted one cycle, and a total of 10 cycles were performed. The mass of the specimen was measured after every 2 cycles, and the mass loss rate was calculated (mass loss rate = (initial mass - mass after cycle) / initial mass × 100%). After 10 cycles, the cohesion was measured by an unconsolidated undrained quick shear test, and the cohesion retention rate was calculated (cohesion retention rate = cohesion after cycle / initial cohesion × 100%). Separately, specimens cured for 28 days and subjected to 3 dry-wet cycles were cut, and the cross-sections were observed using scanning electron microscopy (SEM) at magnifications of 500× and 2000×.

[0073] 1.3 Setting Time and Long-Term pH Stability Test: Under constant temperature conditions of 35±1℃, the substrates obtained from Examples 1-3, Comparative Examples 3, 4, 8, and 11 were mixed with water at a water-cement ratio of 0.3 and the initial and final setting times were determined using the Vicat method. Separately, each substrate was cured at 25±2℃ and 60±5% relative humidity for 28 days, and the pH value was measured weekly at a soil-to-water ratio of 1:5 for 12 consecutive weeks.

[0074] 1.4 Nitrogen Loss Rate Determination: The substrates obtained in Examples 1-3, Comparative Examples 3, 4, 8, and 11 were added with water to a moisture content of 60% and cured at 25±2℃ for 7 days. After curing, rainfall was simulated at a rate of 2.0 L / min for 30 minutes, and all leachate was collected. The total nitrogen content in the leachate was determined using alkaline potassium persulfate digestion-ultraviolet spectrophotometry. Simultaneously, the initial total nitrogen content of the substrate was determined, and the nitrogen loss rate was calculated (nitrogen loss rate = total leached nitrogen / initial total nitrogen content of substrate × 100%).

[0075] 1.5 Slope Erosion Resistance Experiment: A standardized indoor slope model trench (2.0m long × 0.5m wide × 0.3m deep) was constructed with a slope inclination of 35°. Natural soil (bulk density 1.3g / cm³) was filled and reinforced with mesh. The composite substrates obtained in Examples 1-3, Comparative Examples 3, 4, 8, and 11 were uniformly sprayed onto the slope using a spraying process to a thickness of 10cm. A non-woven fabric (15g / m²) was laid on the surface to simulate field protection measures. After curing at 25±2℃ for 7 days, an artificial rainfall erosion experiment was conducted with a fixed rainfall intensity of 2.0L / min (rainfall uniformity ≥85%). Observations were continuous for 30 minutes, and all runoff sediment samples were collected every 5 minutes using a collection bucket. The collected mixture was allowed to settle for 24 hours, the supernatant was removed, and the mixture was dried at 105℃ to constant weight. The cumulative sediment erosion amount over 30 minutes was calculated.

[0076] 1.6 Wind Erosion Test: The substrates obtained from Examples 1-3, Comparative Examples 3, 4, 8, and 11 were cured for 7 days under the conditions described in 1.1, then cut into 10cm×10cm×3cm pieces and placed in the wind tunnel test section. They were subjected to continuous wind erosion for 2 hours at a wind speed of 15m / s and a temperature of 35±2℃. The mass of the test blocks before and after the test was measured, and the wind erosion mass loss rate was calculated.

[0077] 1.7 Water Retention and Drought Resistance Test: A comparative test of water evaporation was conducted using the weighing method. The composite substrates obtained in Examples 1-3, Comparative Examples 5, and Comparative Example 11 were mixed evenly with natural soil at a ratio of 10%, and filled into cylindrical PVC containers (sealed at the bottom) with a diameter of 10 cm and a height of 15 cm. The filling height of each container was 10 cm, and the filling bulk density was controlled at 1.3 g / cm³. Deionized water was added to adjust the initial moisture content to 60% of the field capacity, and the containers were placed in a constant temperature drying oven at 55±2℃. Water replenishment was stopped for 7 consecutive days after the start of the test. On the 7th day, the containers were weighed at regular intervals, and the weight change of each container was recorded. The cumulative water evaporation over 7 days was calculated, and the water retention rate (water retention rate = (initial moisture content - cumulative evaporation over 7 days) / initial moisture content × 100%) was used to evaluate the water retention and drought resistance performance of the substrate.

[0078] 1.8 Salt Surface Polymerization Test: The substrates obtained in Examples 1-3, Comparative Examples 5, and Comparative Example 11 were filled into an acrylic glass soil column with an inner diameter of 5 cm and a height of 20 cm, with a filling height of 15 cm and a bulk density controlled at 1.3 g / cm³. A Marshall bottle was connected to the bottom of the soil column, and simulated groundwater containing NaCl (concentration 0.5 g / L) was continuously supplied, with the liquid level maintained 2 cm above the bottom of the soil column. The soil column was placed in a constant temperature drying oven at 55±2℃ for continuous evaporation for 14 days. After the evaporation, the substrate in the soil column was sampled in layers of 0-1 cm (surface layer) and 3-5 cm (bottom layer). Deionized water was added to each layer at a soil-to-water ratio of 1:5, and the samples were shaken and extracted for 30 min. The EC value of the extract was measured using a conductivity meter, and the salt surface polymerization coefficient was calculated (salt surface polymerization coefficient = surface layer EC value / bottom layer EC value). The closer the salt surface polymerization coefficient is to 1.0, the more uniform the salt distribution between the upper and lower layers, and the better the salt inhibition and surface polymerization performance.

[0079] Table 1: Test results of mechanical properties, corrosion resistance and long-term durability Table 2. Test results of water retention, drought resistance, and salinity regulation. From Table 1 and Table 2, we can see that: The matrices prepared in Examples 1-3 all exhibited a 7-day cohesion ≥25.2 kPa and a pH value ≤7.7, indicating that the overburned magnesium oxide-potassium dihydrogen phosphate composite provided sufficient early consolidation strength while preventing the strong alkalinity of cement from damaging microorganisms and seedling roots. The initial setting time at 35℃ was ≥18 min, indicating that the PHA-coated citric acid particles effectively delayed the flash setting of magnesium phosphate cement under high-temperature conditions through the immediate release of a small amount of citric acid, providing a reasonable operating window for high-temperature construction in dry-hot valleys. After 10 wet-dry cycles, the cohesion retention rate was ≥79.8%, the mass loss rate was ≤4.8%, and the pH value remained between 6.9 and 7.2 after 12 weeks. Observation of microcracks revealed granular calcium citrate deposits, indicating that the PHA-coated citric acid particles continuously degraded and released acid, maintaining long-term pH stability, and the calcium citrate deposition enhanced the bonding strength of the crack surface. The 7-day moisture retention rate was ≥60.5%, and the salt surface aggregation coefficient was ≤4.4, indicating that the water-retaining and salt-blocking components effectively alleviated drought stress and salt infiltration stress through repeated water absorption and release cycles of the water-retaining agent and the salt regulation effect of the modified attapulgite. The cumulative sediment erosion amount in 30 minutes was ≤228g / m², the wind erosion mass loss rate was ≤3.8%, and the nitrogen loss rate was ≤23.5%, indicating that the substrate has good comprehensive resistance to water erosion, wind erosion, and nutrient retention.

[0080] In Comparative Example 4, replacing the overburned magnesium oxide-potassium dihydrogen phosphate compound with ordinary silicate cement resulted in a significant increase in pH to a strongly alkaline range after 7 days. After wet-dry cycles, the cohesion retention rate decreased significantly, and both mass loss and wind erosion loss rates increased significantly. Even after 12 weeks, the pH remained strongly alkaline, indicating that the high alkalinity and high shrinkage of the cement severely impaired the microbial compatibility and long-term anti-expansion / shrinkage durability of the substrate. In Comparative Example 8, replacing PHA-coated citric acid particles with uncoated citric acid significantly shortened the initial setting time at 35°C. After 12 weeks, the pH decreased significantly, and SEM observation revealed no deposits on the surface of microcracks. This indicates that the uncoated citric acid, after its concentrated release in the early stages, exhausted its buffering capacity, failing to achieve long-term pH stability and microcrack repair. In Comparative Example 3, the absence of diatomaceous earth significantly increased the nitrogen loss rate, indicating that diatomaceous earth's ability to absorb NH4+ was compromised. + Electrostatic adsorption is a key mechanism for reducing nutrient leaching. In Comparative Example 5, the moisture retention rate decreased significantly after 7 days due to the absence of a water-retaining agent, indicating that the water-retaining agent plays an irreplaceable role in maintaining the moisture content of the substrate under drought conditions. In Comparative Example 11, the salt surface aggregation coefficient increased significantly due to the use of unmodified attapulgite, indicating that chitosan quaternary ammonium salt modification is the core mechanism for inhibiting salt surface aggregation.

[0081] Experiment Example 2: Survival of microbial agents, synergistic effect of two microorganisms and growth promotion under high temperature and drought conditions (results are shown in Tables 3 and 4). 2.1 High-Temperature Storage Survival Rate Test of Bacterial Agents: 50g of each of the composite substrates obtained in Examples 1-3, Comparative Examples 6, 9, 10, and 12 were spread evenly in sterile petri dishes with a diameter of 9cm (approximately 1cm thick) and placed in a constant temperature incubator at 55±1℃. After 72h, samples were taken, and the survival rate of Bacillus subtilis was determined using the plate counting method: 10g of substrate was added to 90mL of sterile physiological saline, shaken at 180rpm for 30min to fully disperse the bacteria, serially diluted, and spread onto LB agar plates, incubated at 37℃ for 24h, and counted. The germination rate of AMF spores was determined by the step blue staining method: 20g of substrate was taken, and AMF spores were separated by wet sieving and decanting (sieve apertures of 500μm, 250μm, and 45μm). The material on the 45μm sieve was collected, and 0.4% step blue staining solution was added for staining for 10min. The proportion of germinating spores was counted under a microscope (100×) (germination was defined as spores with visible germination tubes extending out, and no less than 200 spores were counted per sample).

[0082] 2.2 Vegetation Promotion Effect Experiment: Using natural soil (passed through a 5mm sieve, bulk density 1.3g / cm³, field capacity approximately 25%) as the substrate, the composite substrates obtained in Examples 1-3, Comparative Examples 2a, and Comparative Example 2b were uniformly mixed with the topsoil (0-5cm depth) at a ratio of 10%, with pure soil without added substrate serving as a blank control. Plastic flowerpots with an upper diameter of 15cm and a height of 12cm were used, each containing 1.5kg of soil. Sudan grass was used as the model plant for the comparative experiment. 60 seeds were evenly sown in each pot (sowing depth approximately 1cm). After sowing, the initial soil moisture content was adjusted to 60% of field capacity using a spray method. The plants were cultivated under conditions of 25±1℃, light intensity of 3000 lux, and photoperiod of 16h / d. During the cultivation period, water was replenished daily using a weighing method to maintain the soil moisture content at 55%-65% of field capacity. On day 28, the seed germination rate was counted (with the first true leaf fully unfolded as the germination standard). A 1cm×1cm grid board was used to cover the surface of the pot, the number of vegetation coverage grids was counted, and the vegetation coverage was calculated.

[0083] 2.3 Determination of plant biomass and mycorrhizal infection rate: After 28 days of cultivation, the aboveground parts of the plants in each treatment group in 2.2 were cut off at the base, and the roots were carefully separated from the soil and rinsed clean with deionized water. The aboveground parts and roots were placed in kraft paper bags and dried in an oven at 65℃ until constant weight (about 48h). The dry weight of the aboveground parts and the dry weight of the roots were measured using an analytical balance. Take fresh fine roots (diameter <1mm), cut them into 1cm segments, add 10% KOH solution, and treat with 90℃ water bath for 30min for clearing. After rinsing with deionized water, acidify with 2% HCl for 5min, add 0.05% Triben Blue staining solution, and stain with 90℃ water bath for 20min. After decolorization, randomly select 30 root segments to prepare slides. Under a microscope (100×), observe the mycorrhizal structure using the grid cross method, count the number of root segments containing arbuscular structures, vesicles, or hyphal circles, and calculate the mycorrhizal infection rate (infection rate = number of infected root segments / total number of observed root segments × 100%).

[0084] Table 3: Results of microbial agent survival rate test Table 4: Test results of synergistic growth-promoting effect of dual bacteria As can be seen from Tables 3 and 4: Examples 1-3 effectively solved key technical problems in the ecological restoration of arid and hot river valley slopes, such as rapid inactivation of bacterial agents under extreme hydrothermal stress and incomplete growth-promoting function of single strains. Specifically, under 55℃ / 72h conditions, the bacterial survival rate was ≥60.2% and the AMF germination rate was ≥50.5%, indicating that the double-shell core-shell structure of calcium alginate-chitosan quaternary ammonium salt combined with proline osmotic protection provided effective protection for the survival of the bacterial agents in high-temperature and arid environments. After 28 days, the germination rate was ≥73.5%, vegetation coverage was ≥63.2%, and mycorrhizal infection rate was ≥44.5%, all significantly improved compared to the control group. The aboveground dry weight and root dry weight were also superior to the control group, indicating that the phosphorus-solubilizing and auxin-secreting functions of Bacillus subtilis and the mycorrhizal symbiotic water absorption function of *Bacillus mosierifolius* formed a synergistic complementary relationship, achieving a dual effect of "growth promotion + drought resistance".

[0085] In Comparative Example 10, the use of free bacterial solution instead of microencapsulated bacterial agent significantly reduced both bacterial survival rate and AMF germination rate, indicating that microencapsulation is a key protective measure for bacterial agent survival in high-temperature and drought environments. In Comparative Example 6, the lack of acclimatization of the bacterial agent resulted in a significant decrease in both bacterial survival rate and AMF germination rate. In Comparative Example 9, the removal of the chitosan quaternary ammonium salt secondary coating led to a decrease in bacterial survival rate, indicating that the chitosan quaternary ammonium salt coating layer makes a substantial contribution to protecting the activity of the bacterial agent. In Comparative Example 12, the absence of proline significantly reduced bacterial survival rate, indicating that proline, as a permeability protectant, is indispensable for maintaining bacterial activity under high-temperature and drought conditions. In Comparative Example 2a, containing only Bacillus subtilis and excluding *Tetranychus mosierifolius*, the mycorrhizal infection rate was 0, and the root dry weight was significantly lower, indicating that AMF mycorrhizal symbiosis makes an independent contribution to expanding the root water absorption range and promoting root development. In Comparative Example 2b, since it contained only *Bacillus mosierifolius* and not *Bacillus subtilis*, the germination rate and aboveground dry weight were both low after 28 days, indicating that the phosphorus-solubilizing and auxin-secreting functions of *Bacillus subtilis* make an independent contribution to promoting seed germination and aboveground growth.

[0086] Experiment Example 3: Secondary fermentation inhibition effect and AMF protection test (experimental results are shown in Table 5).

[0087] 3.1 Secondary Fermentation Temperature Rise Test: Take 300g of each of the composite substrates obtained in Examples 1-3, Comparative Example 1, and Comparative Example 7, add water to a moisture content of 60% (simulating watering after construction), stir evenly, and then put them into a 500mL insulated glass container (the container was preheated to 45℃). Wrap the outer wall of the container with polyurethane foam for insulation. Insert a temperature probe (accuracy ±0.1℃) into the center of the substrate through the central hole of the container lid, and place the container in a constant temperature incubator at 45±1℃. Connect a multi-channel temperature recorder and continuously monitor for 72 hours, automatically recording temperature data every 30 minutes. Record the highest temperature at the center of the substrate and calculate ΔTmax (ΔTmax = highest temperature - initial temperature 45℃). ΔTmax is used to characterize the degree of heat generation during secondary fermentation.

[0088] 3.2 Determination of available nitrogen content: The substrate was soaked in water to a moisture content of 60% and incubated at 45±1℃ for 72 hours before sampling. KCl extraction was used: 10g of substrate (accurate to 0.01g) was added to 50mL of 1mol / L KCl solution and extracted by shaking at 25±1℃ and 180rpm for 1 hour. The extract was collected by filtering with quantitative filter paper. NH4 was determined using the indophenol blue colorimetric method (wavelength 625nm). + NO3- content was determined by ultraviolet spectrophotometry (wavelengths 220 nm and 275 nm). — -N content, the sum of the two is the available nitrogen content.

[0089] 3.3 Determination of AMF spore germination rate: 20g of sample was taken from the substrate after 72h of culture in 3.1. AMF spores were separated by wet sieve decanting (sieve apertures of 500μm, 250μm, and 45μm). The material on the 45μm sieve was collected, stained with 0.4% step blue staining solution for 10min, and observed under a microscope (100×). The proportion of germinating spores was counted (spores with visible germination tubes were counted as germination, and no less than 200 spores were counted per sample).

[0090] Table 5: Results of Secondary Fermentation Inhibition Effect and AMF Protection Test Table 5 shows that: Examples 1-3 effectively solved key technical problems in the ecological restoration of hot and dry valley slopes, including the heat damage from secondary fermentation of organic solid waste after root watering, nitrogen bio-fixation, and the non-target inhibition of AMF spores by tea polyphenols. Specifically, the secondary fermentation ΔTmax was ≤5.2℃, and the available nitrogen content after 72 hours was ≥70.2 mg / kg, indicating that tea polyphenols inhibited microbial protease activity through phenolic hydroxyl groups, and phytic acid inhibited metalloproteinase activity through chelation of metal ions. These two factors synergistically blocked the aerobic metabolic pathways of miscellaneous bacteria, effectively preventing the heat damage from secondary fermentation and nitrogen depletion caused by root watering after substrate spraying, providing a safe temperature and nutrient environment for seedling germination. The AMF spore germination rate was ≥50.5%, indicating that the pre-aging step reduced the free concentration of tea polyphenols after forming hydrogen-bonded complexes with humic acid, effectively reducing non-target contact with *Tetranychus mosieboldii* spores while retaining the inhibitory effect on miscellaneous bacterial fermentation.

[0091] In Comparative Example 1, due to the absence of the tea polyphenol-phytic acid compound, the ΔTmax of secondary fermentation increased significantly, and the available nitrogen content decreased significantly. This indicates that the intense aerobic metabolism of bacteria in the organic solid waste leads to a sharp increase in the internal temperature of the substrate and the large-scale fixation of nitrogen by microorganisms, which will severely burn the seed radicle and cause nitrogen deficiency in seedlings. In Comparative Example 7, because the tea polyphenol-phytic acid compound was not pre-aged, the germination rate of AMF spores decreased significantly. This indicates that the unaged tea polyphenols exist in the substrate in a free state, and after contact with *Tetranychus mosieboldii* spores, they exerted a non-target inhibition on their germination.

Claims

1. A drought-resistant, soil-stabilizing, and vegetation-supporting composite substrate suitable for hot and dry river valleys, characterized in that, Includes the following components by weight: 100 parts of well-rotted sludge nutrient soil, 3-8 parts of microencapsulated bacterial agent, 1.5-4 parts of overburned magnesium oxide-potassium dihydrogen phosphate compound, 0.8-2 parts of composite buffer component, 0.4-1.5 parts of water-retaining and salt-inhibiting component, and 0.3-0.6 parts of tea polyphenol-phytic acid compound; wherein: The composted sludge nutrient soil is the product of deep composting treatment of sludge from urban sewage treatment plants through aerobic composting. The microencapsulated bacterial agent is a double-shell core-shell particle with a mixture of compound growth-promoting bacteria and proline as the core, and sequentially coated with a calcium alginate layer and a chitosan quaternary ammonium salt layer. The compound growth-promoting bacteria consist of heat-resistant Bacillus subtilis and drought-resistant Tuberculosus mosieuria. The composite buffer component is composed of calcium humate, diatomaceous earth, calcium carbonate, and PHA-coated citric acid particles. The water-retaining and salt-inhibiting component is a compound of potassium polyacrylate water-retaining agent and modified attapulgite clay; The modified attapulgite is obtained by modifying attapulgite with chitosan quaternary ammonium salt; The preparation method of the microencapsulated bacterial agent is as follows: The heat-tolerant Bacillus subtilis was fermented and cultured to the logarithmic growth phase. Proline was added to a final concentration of 5-15 mmol / L, followed by the addition of drought-tolerant Coptis chinensis agent, which was stirred evenly. The mixture was then mixed with sodium alginate solution and added dropwise to calcium chloride solution for cross-linking, forming a single-layer microcapsule with a core of compound growth-promoting bacteria and proline, and a shell of calcium alginate. After washing with deionized water, the microcapsule was immersed in chitosan quaternary ammonium salt solution for secondary coating, forming an outer chitosan quaternary ammonium salt layer. The microencapsulated bacterial agent was then vacuum dried to a moisture content ≤15%. The preparation method of the PHA-coated citric acid particles is as follows: Citric acid was pulverized to 50-200 μm to serve as the core material; PHA was dissolved in dichloromethane to prepare a 5-10 wt% solution; citric acid particles were dispersed in the PHA solution, and slowly added to a 0.5-1 wt% polyvinyl alcohol aqueous solution with stirring. After emulsification, the organic solvent was removed by vacuum evaporation, and the solution was vacuum dried until the residual solvent content was below the detection limit; the solidified particles were collected by filtration, washed with deionized water, and dried to obtain PHA-coated citric acid particles with a particle size of 50-200 μm.

2. The drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to claim 1, characterized in that, In the overburned magnesium oxide-potassium dihydrogen phosphate compound, the molar ratio of overburned magnesium oxide to potassium dihydrogen phosphate is 2~4:

1.

3. The drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to claim 1, characterized in that, In the composite buffer component, the mass ratio of calcium humate, diatomaceous earth, calcium carbonate, and PHA-coated citric acid particles is 1:3~5:0.1~0.3:0.5~1; the PHA-coated citric acid particles contain 40~60wt% citric acid, have a weight-average molecular weight of 50000~150000 Da for polyhydroxyalkanoates, and have a particle size of 50~200μm.

4. The drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to claim 1, characterized in that, In the water-retaining and salt-resistant component, the mass ratio of potassium polyacrylate water-retaining agent to modified attapulgite is 1:0.3~0.8; the particle size of the potassium polyacrylate water-retaining agent is 80~120 mesh; and the content of chitosan quaternary ammonium salt in the modified attapulgite is 8~15wt%.

5. The drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to claim 1, characterized in that, The preparation method of the decomposed sludge nutrient soil is as follows: dewatered sludge from urban sewage treatment plants is mixed with corn stalk powder at a wet weight ratio of 1:0.3~0.5, the C / N ratio is adjusted to 25~30:1, the moisture content is 55~65%, and the mixture is inoculated with a high-temperature resistant fermentation agent for aerobic composting treatment. The compost temperature is ≥55℃ for a duration of not less than 15 days, and the total composting cycle is not less than 45 days. After sieving, the GI is ≥80% and EC is ≤3mS / cm to obtain the decomposed sludge nutrient soil.

6. The drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to claim 1, characterized in that, The method for preparing the modified attapulgite is as follows: Attapulgite is thermally activated at 350-400℃ for 2-3 hours and then cooled to room temperature. The thermally activated attapulgite is mixed with a chitosan quaternary ammonium salt solution at a solid-liquid ratio of 1:8-12 and stirred at 60-70℃ for 4-6 hours. After centrifugation, the mixture is washed with deionized water, dried at 80-90℃ to constant weight, and pulverized through an 80-120 mesh sieve to obtain modified attapulgite.

7. A method for preparing the drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to any one of claims 1-6, characterized in that, The tea polyphenol-phytic acid compound is premixed with a portion of the decomposed sludge nutrient soil at a mass ratio of 1:8~12 and aged at 25~30℃ for more than 48 hours. Then, it is mixed with the remaining decomposed sludge nutrient soil and the composite buffer component to obtain the basic premix. Subsequently, microencapsulated bacterial agent and water-retaining and salt-inhibiting components are added and stirred at 25~35℃. Finally, the superburned magnesium oxide-potassium dihydrogen phosphate compound is added and stirred until uniform to obtain the finished product.

8. The application of the drought-resistant, growth-promoting, soil-stabilizing, and vegetation-supporting composite substrate according to any one of claims 1-6 in the ecological restoration of steep slopes in dry and hot river valleys.

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