Method for promoting decomposition of litter in north china larch plantation

Abstract

The present application relates to the technical field of forest management, and particularly relates to a method for promoting decomposition of litter in Larix principis-rupprechtii artificial forest. The method comprises the following steps: S1, reducing canopy density by differential thinning; S2, cleaning and physically crushing the Larix principis-rupprechtii litter layer of the thinning belt, and spreading the crushed litter in the cleaned forest land and / or forming an accumulation belt 0.5 meters away from the plant on both sides; S3, artificially inoculating biological inoculants and increasing nitrogen fertilizer to accelerate the decomposition of litter; wherein the artificial inoculation of biological inoculants comprises inoculating Trichoderma-Penicillium complex inoculants on the surface layer of litter, injecting inoculant-water retaining agent complex in the middle layer, and spraying chitosan solution on the bottom layer; the increase of nitrogen fertilizer comprises embedding slow-release nitrogen fertilizer on the surface layer of litter, loading long-acting nitrogen in the middle layer, and spraying quick-acting nitrogen fertilizer on the bottom layer; S4, directional re-planting of nitrogen-fixing shrubs and sowing of herbaceous plants to construct a multi-element shrub-grass community. The present application has important significance for repairing the soil function of Larix principis-rupprechtii artificial forest, fertilizing the soil, activating nutrient circulation, promoting the regeneration succession of Larix principis-rupprechtii, and realizing the sustainable development of forest ecosystem.

Description

Technical Field

[0001] This invention relates to the field of forest management technology, and in particular to a method for promoting the decomposition of litter in larch plantations in North China. Background Technology

[0002] As a unique tree species in the alpine coniferous forest belt of North China, the North China larch is a core force in the construction of national greening and ecological security barriers. Widely distributed in the upper mountain areas of Hebei, Shanxi, and other provinces, it plays a crucial role in maintaining soil and water conservation, water resources, biodiversity, improving the regional ecological environment, reducing wind and sand damage, and regulating climate through its dense canopy intercepting rainfall and its extensive root network holding the soil. However, current North China larch plantations face a significant imbalance in the ecological function of litter. Due to the long-term monoculture management model, the annual accumulation of litter under the forest canopy is excessive, generally exceeding 10 cm in thickness, and the decomposition rate is extremely low, less than half that of litter in mixed coniferous and broadleaf forests. The thick litter layer forms a dense physical barrier, hindering rainwater infiltration and root respiration, leading to a significant decrease in soil aeration, compression of effective microbial activity space, and consequently, stagnation of soil organic matter mineralization, depletion of available nutrients, and a significant reduction in overall soil fertility compared to mixed forests, exhibiting a clear trend of degradation. According to field investigations, the litter from larch plantations in North China share common characteristics such as high cellulose content, lignin content, C / N ratio, thick accumulation, small contact area with soil microorganisms, cold climate leading to low soil microbial activity, and limited litter species.

[0003] Traditional mechanical tillage methods bury larch litter beneath the soil, disrupting the original soil layers and damaging the topsoil humus layer (O layer) and soil aggregates. This leads to decreased soil porosity, particularly reduced aeration porosity, severely impacting root respiration. Furthermore, during the rainy season in the North China mountains, tilling forest soil exacerbates soil erosion. In addition, tillage brings deep-seated anaerobic bacteria to the surface while burying aerobic decomposing bacteria, resulting in a slower litter decomposition rate and decreased soil enzyme activity. Moreover, mechanical tillage poses safety risks on slopes, and the high labor and machinery costs lead to a significant increase in long-term costs. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the problems of slow decomposition of larch litter, poor nutrient cycling, and resulting soil function decline, this invention provides a method for promoting the decomposition of larch litter in larch plantations in North China. This method enables a paradigm shift in larch plantation litter from "litter accumulation-type degradation" to "nutrient cycling-type health," which is of great significance for restoring soil function, enriching soil, activating nutrient cycling, promoting the regeneration and succession of larch, and achieving sustainable development of the forest ecosystem.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a method for promoting the decomposition of litter in larch plantations in North China, comprising the following steps:

[0008] S1. Reduce canopy closure through differentiated thinning;

[0009] S2. Clean and physically break up the larch litter layer in the thinning zone, and spread the broken litter in the cleared forest area and / or form a pile strip 0.5 meters away from the trees on both sides;

[0010] S3. Artificial inoculation with biological agents and increased application of nitrogen fertilizer to accelerate the decomposition of litter;

[0011] The artificial inoculation of biological agents includes inoculating the surface of the litter with a Trichoderma-Penicillium compound agent, injecting a compound agent-water-retaining agent into the middle layer, and spraying a chitosan solution at the bottom layer; the additional application of nitrogen fertilizer includes embedding slow-release nitrogen fertilizer in the surface of the litter, loading long-acting nitrogen in the middle layer, and spraying fast-acting nitrogen fertilizer at the bottom layer.

[0012] S4. Targeted replanting of nitrogen-fixing shrubs and sowing of herbaceous plants to construct a diverse shrub-grass community.

[0013] According to a preferred embodiment of the present invention, in S1, the differentiated thinning method is as follows: growth thinning is carried out on middle-aged / near-mature forests; Class V trees, Class IV trees and some Class III trees are removed to maintain the canopy closure at 60-65% and improve the light and heat conditions under the forest.

[0014] Among them, Grade V trees are dying / dead trees, characterized by a crown loss rate >75%, dead tips or decayed trunks, extremely weak photosynthetic capacity, posing a source of pests and diseases, and having almost no growth potential. Grade IV trees are compressed trees, characterized by crowns squeezed by upper branches (side branches withered), abnormal height-to-diameter ratio, stagnant growth, and an irreversible competitive disadvantage. Grade III trees are moderately viable trees, characterized by a crown integrity of 60-80%, subject to some lateral compression but still having room to grow. Grade III trees are selectively removed, only thinning out overly dense areas, retaining individuals with excellent trunk shapes as reserve target trees.

[0015] Differential thinning can reduce canopy closure and achieve the following effects: ① Reduce stand density, directly reducing the annual accumulation of litter; ② Improve understory water and heat conditions and increase understory light intensity, providing basic light conditions and growth space for the planting of shrubs and grasses; ③ Increase the variety of litter, increase light, and alleviate the inhibitory effect of low temperatures on microorganisms in high-altitude areas.

[0016] According to a preferred embodiment of the present invention, step S2 is as follows: using a pulverizer to crush larch litter, the crushed particle size is controlled to be 2-5cm; the crushed litter is spread and piled up in a ratio of 7:3, 70% of the crushed litter is evenly spread in the cleaned area, and a loose layer with a thickness of 5-10cm is spread; the remaining 30% of the crushed litter is mixed with the collected broadleaf tree leaves in a ratio of 1:1-2, and after mixing, it is piled up 0.5 meters away from both sides of the larch plant to form a compound pile strip 1-1.5m high and 10-20cm wide, with a spacing of 1-2m between the compound pile strips.

[0017] The crusher is a disc rake crusher; when crushing litter, the surface layer (5-10 cm thick) of the litter layer in forest gaps and thinning zones with a thickness >15 cm is crushed. The broad-leaved trees are mainly birch (birch C / N≈23), aspen, etc. These broad-leaved tree litter have low carbon content (low C / N ratio). The crushed broad-leaved tree litter is mixed with the crushed larch litter to reduce the C / N ratio of the larch litter from 80:1 to below 50:1, creating a low carbon-nitrogen ratio environment for subsequent inoculation with biological agents.

[0018] Larch litter has a high C / N ratio, and microbial decomposition requires maintaining a metabolic balance of C / N ≈ 24. Therefore, when nitrogen is scarce, microorganisms need to fix nitrogen from the soil, leading to their accumulation in the soil and a significant decrease in litter decomposition efficiency. Furthermore, larch litter has a high lignin content (15-25%), requiring microorganisms to consume more energy to synthesize lignin-degrading enzymes (such as laccase and peroxidase), resulting in low microbial activity and limited growth and reproduction.

[0019] Cleaning and physically breaking up litter can remove physical barriers, which has the following effects: ① Reduces the smothering and suppression of shrub and grass seedlings by litter, improving seedling emergence rate, survival rate, and natural regeneration success rate; ② Optimizes the physical structure of litter decomposition by crushing and cleaning, significantly increasing the specific surface area of ​​the litter, exposing more cellulose and lignin sites, and improving microbial contact efficiency (the epidermis of larch needles contains hydrophobic waxes and terpenoid resins, which hinder water penetration and enzyme contact, prolonging the softening period and slowing the decomposition initiation; the fresh wounds created by excessive crushing can significantly accelerate the decomposition process); ③ The natural decomposition of the accumulated area and its synergistic effect with the subsequent inoculation of biological agents produce a large amount of humus, providing a continuous nutrient supply for shrub and grass growth.

[0020] According to a preferred embodiment of the present invention, in S3, the treatment method for the surface of the litter is as follows: a compound microbial agent containing Trichoderma and Penicillium is mixed evenly with forest humus soil and slow-release nitrogen fertilizer, and then applied to the surface of the litter in the cleaned area within 24 hours after rain to increase the variety of microorganisms. The slow-release nitrogen fertilizer is sulfur-coated urea. The nitrogen fertilizer provides a nitrogen source for microorganisms, promotes the rapid colonization of Trichoderma and Penicillium, and at the same time, sulfur-coated urea slowly releases nitrogen (the release peak is from June to August), which is synchronized with the peak period of microbial agent decomposition.

[0021] The treatment method for the middle layer of litter is as follows: Starch-based water-retaining agent, straw fiber, starch binder, microbial spores, and urea-formaldehyde slow-release nitrogen fertilizer are made into cake-shaped slow-release blocks with a diameter of 10-20cm and a thickness of 3-7cm (preferably 10-15cm in diameter and 3-5cm in thickness). The starch-based water-retaining agent, urea-formaldehyde slow-release nitrogen fertilizer, and microbial spores are wrapped in the inner layer of the cake-shaped slow-release blocks to obtain a microbial agent-water-retaining agent composite carrying long-acting nitrogen. Shallow pits of 5-8cm depth are dug in the litter layer, the microbial agent-water-retaining agent composite is placed in, and then the fallen leaves are covered. The composites are arranged at fixed points at intervals of 3-5m in the litter accumulation zone, with 20-30 per acre.

[0022] The treatment method for the bottom layer of litter is as follows: Ammonium nitrate is added to chitosan solution to prepare a composite solution with a nitrogen concentration of 2.5-3.5 g / L and a chitosan concentration of 0.8-1.2%; after inoculating the surface of litter with the composite microbial agent for 10-20 days, the composite solution is sprayed onto the surface of litter using a spraying device. The composite solution penetrates to the bottom layer of litter under the action of gravity; 50-80 L is sprayed per acre.

[0023] According to a preferred embodiment of the present invention, in S3, the ratio of Trichoderma to Penicillium in the compound microbial agent is 2:1, and the viable count of the compound microbial agent is ≥5×10⁻⁶. 8 CFU / g; the humus soil consists of forest undergrowth with a particle size of 2-5 mm and a moisture content of 20-25%; the nitrogen slow-release period of the sulfur-coated urea granules is 2 months, with a particle size of 1-2 mm. The compound microbial agent, humus soil, and slow-release nitrogen fertilizer are mixed evenly at a mass ratio of 1:10:2, and the application rate is 50-80 kg / hm². 2 .

[0024] According to a preferred embodiment of the present invention, in S3, when preparing the microbial agent-water-retaining agent complex carrying long-acting nitrogen, the nitrogen content of the urea-formaldehyde slow-release nitrogen fertilizer is 35-45%, and the amount of starch-based water-retaining agent is 25-40%. The microbial agent spores are at least one of white-rot fungi (such as Phanerochaete chrysosporium), brown-rot fungi, actinomycetes, green streptomyces, and putrefactive pseudomonas, preferably a combination of white-rot fungi and actinomycetes, which can shorten the decomposition half-life of litter by 40-50%. In the early stage of decomposition, organic acids (pH 4.2-5.0) are released, which inhibit the activity of most bacteria, and only acid-resistant fungi such as white-rot fungi can participate. Moreover, white-rot fungi directionally degrade lignin.

[0025] According to a preferred embodiment of the present invention, in S3, after placing the microbial agent-water-retaining agent complex carrying long-acting nitrogen into the shallow pit and covering it with fallen leaves, 30-50g of decomposed sheep manure is added around the microbial agent-water-retaining agent complex around each pit to construct a micro-environment of microorganisms-nitrogen fertilizer-organic matter.

[0026] According to a preferred embodiment of the present invention, in step S3, chitosan is dissolved in an aqueous acetic acid solution with a pH of 5.5-6.5, and ammonium nitrate and 0.1% Tween 80 are added to prepare a nitrogen-containing compound solution. The compound solution is sprayed onto the surface of litter and, under the action of gravity, penetrates downward to the bottom layer of the litter, stimulating the proliferation of indigenous microorganisms.

[0027] To address the issues of high cellulose and lignin content in litter from larch plantations in North China, as well as poor soil microbial activity and diversity, step S3 of this invention combines inoculation with the application of biological agents and nitrogen fertilizer. The surface layer is inoculated with a compound microbial agent and slow-release nitrogen fertilizer, allowing *Trichoderma* and *Penicillium* to rapidly colonize the litter. The middle layer is buried with a microbial agent-water-retaining agent complex carrying long-acting nitrogen, promoting local enrichment of nitrogen and microorganisms and continuously supplying active microorganisms to the surrounding litter. The bottom layer is sprayed with chitosan solution and fast-acting nitrogen fertilizer to activate the proliferation of indigenous microorganisms, increasing the amount of soil microorganisms.

[0028] According to a preferred embodiment of the present invention, in S4, the measure for targeted replanting of nitrogen-fixing shrubs is as follows: during the rainy season of the second year after implementing step S3, nitrogen-fixing shrub seedlings are transplanted and planted in a triangular layout, with a spacing of 3-5m between plants / clumps and a density of [missing information - likely a density per hectare]. 2 Plant 60-120 seedlings per clump, dipping the roots of the nitrogen-fixing shrubs in a mud slurry containing mycorrhizal fungi to improve survival rate. The nitrogen-fixing shrub seedlings are lilac or lespedeza, etc., and the amount of mycorrhizal fungi added to the mud slurry is 0.5-2 wt%, preferably 1 wt%.

[0029] The method for sowing herbaceous plants in forest gaps is as follows: Every year from May to June, sow grass seeds at the edge of the forest gaps at a rate of 4-6 kg / hm². 2After sowing, cover the seeds with a shade net with a light transmittance of 38-42% to keep the soil in the forest gaps moist and ensure successful germination. The preferred grass species are sedge and Thalictrum, which are adapted to the climate of larch plantations in North China. They have good shade tolerance, a low photosynthetic compensation point, and, more importantly, a moderate C / N ratio (25-30) in their leaves, resulting in rapid litter decomposition and accelerated nitrogen turnover within the forest gaps. Furthermore, these grass roots can secrete organic acids to activate soil phosphorus, alleviating soil depletion caused by long-term continuous cropping in plantations.

[0030] (III) Beneficial Effects

[0031] This invention addresses several key limiting factors affecting litter decomposition in North China larch plantations, including excessively high density, thick and monoculture of litter, high cellulose, lignin, and C / N ratios, small contact area with soil microorganisms, poor soil microbial diversity, and low biological activity. Through optimizing stand structure, removing and breaking up litter, inoculating with biological agents, and increasing nitrogen fertilizer application, this invention effectively solves the problem of slow litter decomposition in North China larch plantations. Compared to traditional mechanical tillage methods, this invention causes less damage to the soil structure and native microorganisms, requires less machinery, helps protect native soil layers and soil microbial communities, and allows for zoned management of inter-forest application and deposition, concentrating decomposition-promoting measures in target areas and avoiding ecological disturbance from whole-forest intervention.

[0032] In this invention, the initial decomposition rate of litter is significantly increased by crushing the litter. Combined with a suitable microbial agent and increased nitrogen fertilizer application, the thickness of the litter is significantly reduced within one year. Under the synergistic effect of crushing and the compound microbial agent, the degradation rates of cellulose and lignin are significantly higher than those achieved with a single microbial agent.

[0033] Traditional methods involve inoculating the surface of litter with microbial agents to promote degradation. While this increases the variety of microorganisms and accelerates decomposition, the activity of the microorganisms diminishes in the middle and bottom layers, leading to insufficient decomposition rate. The method of this invention employs a multi-layered, comprehensive biological inoculation approach: surface inoculation with a composite microbial agent – ​​middle layer embedding a long-acting nitrogen + microbial agent + water-retaining agent complex – bottom layer activation with chitosan and fast-acting nitrogen. This not only effectively increases the variety of microorganisms but also stimulates the proliferation of native microorganisms, making the efficiency of this method in promoting litter decomposition significantly more pronounced.

[0034] Traditional methods of inoculating the surface of litter with microbial agents only provide short-term relief and cannot fundamentally solve the problem of slow litter decomposition in larch plantations in North China, nor can they establish a healthy dynamic self-cycle. Constructing a multi-layered biological community structure that combines trees, shrubs, and herbaceous plants, as well as conifers and broadleaf trees, is the fundamental way to achieve efficient litter decomposition, accelerate nutrient cycling, and maintain forest ecological balance. To this end, this invention proposes a four-dimensional technical system: "physical fracturing and drag reduction - layered application of slow-growth nitrogen fertilizer - biological microbial catalysis - plant community synergy." While ensuring eco-friendliness, this system significantly improves litter decomposition efficiency, effectively promotes the restoration of soil function and enhances soil fertility in larch plantations in North China, further activates forest nutrient cycling, and has good ecological benefits and application value. Attached Figure Description

[0035] Figure 1 A flowchart of methods to promote the decomposition of litter in larch plantations in North China.

[0036] Figure 2 This is a schematic diagram illustrating the construction of a multi-species shrub-grass community in the method of this invention.

[0037] Figure 3 This is a schematic diagram showing the location of the accumulation zone after the debris has been cleaned and crushed in the method of the present invention. Detailed Implementation

[0038] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Years of research have confirmed that the main reasons for the slow decomposition of litter in larch plantations are as follows: First, the high stand density and sparse understory shrubs and grasses result in a thick accumulation of litter of a single species, especially in pure stands where the litter thickness is much greater than in mixed stands. This excessive litter accumulation also reduces the contact area with soil microorganisms, slowing down the decomposition process. Second, larch is a coniferous tree, and its litter contains high levels of cellulose, lignin, and a high C / N ratio. Furthermore, the surface litter is acidic, leading to poor soil microbial diversity and an underdeveloped microbial community. Third, the cold climate at high altitudes severely limits the activity and duration of microorganisms that decompose litter, resulting in low decomposition efficiency and the accumulation of large amounts of litter over the years.

[0040] To address the technical challenges of slow litter decomposition in larch plantations, the difficulty in rapidly returning nutrients from litter to the soil, slow soil nutrient cycling, and significantly lower overall soil fertility compared to mixed forests, this invention proposes a method to promote litter decomposition in larch plantations in North China. This method optimizes stand structure through differentiated thinning, targeted replanting of shrubs and grasses to construct a diverse community, increasing the variety of litter types and accelerating decomposition. Furthermore, the litter is pulverized and layered for stratified management, creating favorable growth space for shrubs and grasses. A combination of measures is applied to the surface, middle, and deep layers of the litter, including the introduction of biological agents and increased nitrogen fertilizer, adjusting the carbon-nitrogen ratio of the litter, increasing the variety and activity of microorganisms, and maintaining their sustainability. These measures, combined with the self-regulating and restorative capabilities of the ecosystem, stimulate the activity of native microorganisms and promote the proliferation of native vitamins, thereby achieving a paradigm shift from "litter accumulation-induced degradation" to "nutrient cycling-induced health" in larch plantations. This invention is of great significance for promoting the return of nutrients contained in litter to the soil, restoring the soil function of larch plantations in North China, enriching the soil, activating nutrient cycling, promoting the regeneration and succession of larch in North China, and realizing the sustainable development of forest ecosystems.

[0041] The following description is based on preferred embodiments of the present invention.

[0042] Example 1

[0043] like Figure 1 As shown in the figure, this embodiment provides a method for promoting the decomposition of litter in larch plantations in North China, which includes the following steps one to four:

[0044] Step 1: Reduce canopy closure through differentiated thinning. Specific measures are as follows:

[0045] (1) Implement growth cutting in middle-aged / near-mature forests, removing Class V trees, Class IV trees and some Class III trees (individuals with poor growth), maintaining a canopy closure of 60-65%, and improving the water and heat conditions under the forest.

[0046] By using the aforementioned differentiated thinning, forest density is reduced, directly decreasing the annual accumulation of litter, improving understory water and heat conditions, and increasing understory light intensity. This not only provides basic light conditions and growing space for the planting of shrubs and grasses, but also increases the variety of litter, increases sunlight, and to some extent alleviates the inhibitory effect of low temperatures on microbial activity in high-altitude areas.

[0047] Step Two: Clean and physically break up the larch litter layer in the thinning zone, spreading the broken litter in the cleared area and / or forming a stockpile 0.5 meters away from the trees on both sides. Specific measures are as follows:

[0048] For litter layers thicker than 15cm in forest gaps and thinning zones, first use a disc rake shredder to break them up, controlling the particle size to 2-5cm. Then, treat the broken litter according to a "70% spread + 30% pile" ratio: evenly spread 70% of the broken litter in the cleared area to form a loose layer 5-10cm thick, accelerating decomposition through the fresh wounds created by the breaking up. Mix the remaining 30% of the broken litter with collected birch and aspen broadleaf tree leaves in a 1:1 ratio and pile it 50cm away from the trees on both sides, forming a compound pile strip 1-1.5m wide and 10-20cm high, spaced 1-2m apart. Figure 3 After compounding, the C / N ratio of litter decreased from 80:1 to below 50:1, creating a low carbon-nitrogen ratio environment for subsequent inoculation with microbial agents.

[0049] By clearing and physically breaking up litter, the physical barriers of litter can be removed. On the one hand, this reduces the covering and suppression of shrub and grass seedlings by litter, improving the germination rate, survival rate, and natural regeneration success rate of shrub and grass seedlings. On the other hand, crushing and clearing optimize the physical structure of litter decomposition, significantly increasing the specific surface area of ​​litter, exposing more cellulose and lignin sites, and improving microbial contact efficiency. In addition, the natural decomposition of the accumulated area and its synergistic effect with the subsequent inoculation of biological agents produce a large amount of humus, providing a continuous nutrient supply for shrub and grass growth.

[0050] Step 3: Artificially inoculate with biological agents and apply nitrogen fertilizer to accelerate the decomposition of litter.

[0051] The artificial inoculation with biological agents includes inoculating the surface of the litter with a Trichoderma-Penicillium compound agent, injecting a compound agent-water-retaining agent into the middle layer, and spraying a chitosan solution at the bottom. The application of nitrogen fertilizer includes embedding slow-release nitrogen fertilizer into the surface of the litter, loading long-acting nitrogen fertilizer into the middle layer, and spraying a quick-acting nitrogen fertilizer at the bottom. Specific measures are as follows:

[0052] (1) Surface inoculation with slow-release nitrogen fertilizer

[0053] Mixing Trichoderma and Penicillium at a ratio of 2:1 yields a viable count ≥5 × 10⁻⁶. 8 A compound microbial agent with CFU / g concentration. Mix the compound microbial agent, forest understory humus soil (2-5mm particle size, 20% moisture content), and sulfur-coated urea granules (containing 30% nitrogen, 0% phosphorus and potassium, 1-2mm particle size, slow-release period of 2 months) at a ratio of 1:10:2 to obtain the compound. Apply the compound evenly to the surface of litter in the cleared area within 24 hours after rain to increase the diversity of microorganisms. The application rate is 50-80 kg / hm². 2 Nitrogen fertilizer provides nitrogen source for microorganisms, promoting the rapid colonization of Trichoderma and Penicillium. At the same time, sulfur-coated urea slowly releases nitrogen (peak release period from June to August), coinciding with the peak decomposition period of the inoculant.

[0054] (2) Bury cake-shaped slow-release blocks containing long-acting nitrogen, bacterial agent and water-retaining agent in the middle layer.

[0055] Straw fiber and starch binder are used as the outer layer, and microbial spores, starch-based water-retaining agent, and urea-formaldehyde slow-release nitrogen fertilizer (40% nitrogen content) are wrapped in the inner layer to make a cake-shaped slow-release block with a diameter of about 10 cm and a thickness of 3 cm. Shallow pits 5-8 cm deep are dug in the litter layer, the cake-shaped slow-release blocks are placed in the pits, and then covered with fallen leaves. These blocks are arranged at intervals of 3-5 m in the litter accumulation zone, with 20-30 blocks per acre. When covering with fallen leaves, 50g of well-rotted sheep manure (C / N = 10:1) is added around the cake-shaped slow-release blocks to form a "microorganism-nitrogen fertilizer-organic matter" microzone, promoting local nitrogen enrichment (total nitrogen contribution of approximately 35-60 kg / hm²). 2 ).

[0056] The inner layer comprises approximately 75% (15% nitrogen fertilizer, 30% starch-based water-retaining agent, and the remainder being microbial spores), while straw fiber and starch binder comprise approximately 25%. The microbial spores are a combination of white-rot fungi (such as *Phanerochaete chrysosporium*) and actinomycetes. The starch binder is an environmentally friendly adhesive made primarily from natural starch through physical, chemical, or enzymatic modification; it is biodegradable, regenerable, and non-toxic. The starch-based water-retaining agent can absorb 300-500 times its own weight in water, forming a localized high-humidity microzone (humidity > 65%) around the cake-shaped slow-release block. This maintains continuous microbial activity (e.g., white-rot fungi require humidity > 55% to secrete ligninase), addressing the problem of stagnant litter decomposition caused by drought in North China. Starch-based water-retaining agents contain soluble polysaccharides (such as dextrin), which can serve as an auxiliary carbon source for microorganisms. Together with urea-formaldehyde slow-release nitrogen fertilizer (C / N≈8:1), they can synergistically regulate the C / N ratio of micro-regions to the ideal decomposition threshold of 25-30.

[0057] (3) Spray chitosan and available nitrogen at the bottom layer to activate the proliferation of microorganisms in the bottom soil.

[0058] Chitosan was dissolved in a dilute acetic acid aqueous solution with a pH of 5.5-6.5. Tween 80 was added (to enhance the permeability of the solution) to obtain a chitosan solution. Ammonium nitrate was then added to the chitosan solution to prepare a composite solution with an ammonium nitrate concentration of 3 g / L and a chitosan concentration of 1%. The composite solution was then sprayed evenly onto the surface of larch litter at a rate of 50-80 L per acre, contributing approximately 15-24 kg / hm² of pure nitrogen. 2 The compound solution relies on gravity to penetrate to the bottom layer of litter (penetrating downwards 8-10cm), stimulating the proliferation of indigenous microorganisms and increasing the soil microbial biomass.

[0059] Glycan acts as an inducer of resistance signals and a dual-function agent with both antibacterial and growth-promoting effects: Chitosan decomposition products (such as chitooligosaccharides), as quorum sensing molecules of microorganisms, stimulate indigenous actinomycetes (such as Streptomyces) and white-rot fungi (such as Trametes) to secrete lignin-degrading enzymes (laccase, manganese peroxidase). Chitosan can also inhibit pathogenic bacteria (such as Fusarium) in litter, and promote the colonization of beneficial bacteria (such as Pseudomonas) at the same time. Chitosan forms a semi-permeable membrane on the surface of litter, regulates the water infiltration rate, avoids rapid loss of ammonium nitrate, and maintains air permeability at the same time. Ammonium nitrate provides available NH4 + and NO3 - , reducing the C / N of the litter layer to about 25 and relieving the nitrogen limitation of microorganisms.

[0060] The above measures have the following effects: ① By artificially introducing efficient degrading microbial communities, the decomposition rates of cellulose and lignin are significantly improved, a symbiotic environment is provided for indigenous microorganisms, and microbial diversity is increased; ② The comprehensive top-down application of composite microbial agents, humus soil, water-retaining agents and chitosan forms a three-dimensional carbon-nitrogen regulation and decomposition-promoting network of "upper layer inoculation - middle layer slow release - bottom layer activation", which effectively reduces the C / N ratio in litter and improves the litter decomposition efficiency; the addition of slow-release - long-acting - available nitrogen fertilizer makes the change trend of carbon-nitrogen ratio (C / N) more consistent with the metabolic activity cycle of the microbial agents, maintains the sustainability of microbial activity, and improves the microbial catabolic rate; ④ The coupling is realized through the microorganism-nutrient cycle, producing a synergistic effect and improving the catabolic rate.

[0061] Step 4: Targeted replanting of nitrogen-fixing shrubs and sowing of herbaceous plants to construct a diverse shrub-herb community. The specific measures are as follows:

[0062] In the rainy season (July to August) of the second year after thinning, shrub seedlings such as Syringa and Lespedeza are transplanted, adopting a "triangular" layout with a spacing of 3-5m between plants (clumps) and a density of 60-120 plants (clumps) / hm 2 , the roots are dipped in mud, and 1% mycorrhizal fungal agent is added to the mud to improve the survival rate. From May to June every year, grass seeds such as Carex and Thalictrum are sown by broadcasting at the edge of forest gaps, with a sowing rate of 5kg / hm 2 , covered with a sunshade net with a light transmittance of 40% to keep the soil moist until seedling emergence (as shown Figure 2 in the figure).

[0063] The mycorrhizal fungal agent is a biological preparation made of spores, mycelium or propagules of Mycorrhizal Fungi, which is used for artificial inoculation of plant roots to form mycorrhizal symbionts. This symbiotic relationship can significantly improve the absorption efficiency of plants for water and nutrients, and enhance stress resistance.

[0064] Application Example 1

[0065] This invention has been applied in the Jingoutun Forest Farm of Luanping State-owned Forest Farm in Chengde City, Hebei Province, and the Wangxidong Forest Farm of Xiaowutaishan National Nature Reserve in Hebei Province, both planted with North China larch trees.

[0066] I. Overview of the Experimental Site

[0067] Jingoutun Forest Farm Experimental Site, Luanping State-owned Forest Farm: Located in the Chaohe River Basin of Luanping County, Hebei Province, in a concentrated distribution area of ​​North China larch plantations; forest age 43 years, pure forest canopy closure 0.85, 1073 trees / hectare, average diameter at breast height 16.2 cm, litter thickness 12-18 cm, C / N ratio 85:1, single tree species, understory shrub and grass coverage 15.8%.

[0068] Wangxidong Forest Farm Experimental Site, Xiaowutaishan National Nature Reserve: Xiaowutaishan National Nature Reserve, Hebei Province, subalpine coniferous forest zone; forest age 48 years, pure forest canopy closure 0.90, 1575 trees / hectare, average diameter at breast height 14.4 cm, litter thickness 20-25 cm, C / N ratio 90:1, understory shrub and grass cover 5.6%; microbial activity period <5 months, significantly affected by low temperature stress.

[0069] II. Experimental Design

[0070] At the Jingoutun Forest Farm and Wangxidong Forest Farm experimental sites, treatment groups (T) were established, each covering an area of ​​8 mu (approximately 0.33 hectares), and were designated as the Jingoutun T group and the Wangxidong T group, respectively, implementing differentiated thinning, shrub and grass replanting, litter pulverization and cleanup, microbial inoculation, and nitrogen fertilizer regulation. Control groups (CK) received no intervention in litter decomposition and were designated as the Jingoutun CK group and the Wangxidong CK group. After the measures were implemented, the litter thickness, humus layer thickness, litter volume, topsoil (0-20cm) organic matter content, and total nitrogen content were measured in both the treatment and control areas. These indicators were measured again three years after the measures were implemented.

[0071] III. Implementation Plan

[0072] 1. Differentiated thinning (May 2020)

[0073] In areas with a canopy closure greater than 80%, thinning should be carried out to reduce the canopy closure to 60%.

[0074] 2. Litter crushing and stratification management (June-July 2020)

[0075] Use a disc rake shredder to break up the surface litter. After shredding, clean up the litter and set it aside. Spread 70% of the broken litter evenly in the cleared area between rows of North China larch trees to form a loose layer 3-4m wide and 5-8cm thick. Mix the remaining 30% of the broken litter with the collected birch leaves at a 1:1 ratio and pile it 50cm away from the trees on both sides, 1.2m wide and 10-20cm high, with a 2m spacing between the piles, to reduce the local C / N ratio of the litter to below 50:1.

[0076] 3. Inoculation with biological agents and regulation of nitrogen fertilizer (July-August 2020)

[0077] Surface layer of fallen debris: Inoculate with compound microbial agent + slow-release nitrogen fertilizer. Mix 1 part by weight of Trichoderma-Penicillium compound microbial agent, 10 parts of humus soil, and 2 parts of sulfur-coated urea granules (nitrogen-phosphorus-potassium = 30-0-0) evenly to obtain a compound. Apply this mixture evenly to the surface layer of the cleared and piled debris area within 24 hours after rain, at a rate of 50 kg / hm². 2 .

[0078] Middle layer of litter: While applying the compound microbial agent to the surface layer, dig shallow pits 5-8cm deep in the litter layer, and place cake-shaped slow-release blocks with a diameter of 10cm and a thickness of 3cm at 3m intervals, then cover with fallen leaves. The outer layer of the cake-shaped slow-release blocks is straw fiber + starch binder, and the inner layer is white-rot fungi + actinomycetes + starch-based water-retaining agent + urea-formaldehyde slow-release nitrogen fertilizer, 24 blocks per acre. When covering with fallen leaves, add 50g of well-rotted sheep manure around the cake-shaped slow-release blocks. The cake-shaped slow-release blocks contain 15% nitrogen fertilizer, 30% starch-based water-retaining agent, approximately 25% straw fiber and starch binder, and the remainder is microbial spores.

[0079] Bottom layer of litter: Prepare a composite solution by mixing chitosan, Tween 80, ammonium nitrate, and water in a mass ratio of 10:1:8.8:980.2. Spray the composite solution onto the surface of the litter, applying 50L evenly per acre. The composite solution will penetrate into the bottom layer of the litter under gravity.

[0080] 4. Replanting grass and water (May-August 2021)

[0081] Lilac, Lespedeza, and Caragana were planted along the edge of the forest window, with a spacing of 3 meters between plants, per hectare. 2 Plant 60 seedlings (dipping their roots in mud slurry with 1% mycorrhizal fungicide added); also sow 5 kg / hm² of sedge and Thalictrum seeds along the edge of each forest window. 2 .

[0082] IV. Test Results

[0083] The experimental results are detailed in Tables 1 and 2. The litter thickness and volume in the treatment group with accelerated litter control measures were significantly lower than those in the control group (CK), indicating that the measures of "differentiated thinning + litter crushing and cleaning + microbial inoculation + nitrogen fertilizer regulation + shrub and grass replanting" significantly improved the decomposition rate of litter. Simultaneously, the humus layer thickness, topsoil organic matter content, and total nitrogen content in the treatment group were significantly increased compared to the control group, indicating that this method also increased the humus layer thickness and soil nutrient content of the North China larch plantation.

[0084] Table 1. Experimental results at the Jingoutun Forest Farm experimental site

[0085]

[0086] Table 2. Experimental Results at Wangxidong Forest Farm Experimental Site

[0087]

[0088] Comparative experiments at different altitudes in Luanping and Xiaowutai demonstrate the practical applicability of the proposed solution under various site conditions. It significantly reduces litter thickness and accumulation compared to the control group (CK group), while effectively increasing the thickness of the humus layer and enhancing the organic matter and nitrogen content of the topsoil. While ensuring eco-friendliness, it significantly improves litter decomposition efficiency, effectively promoting soil function restoration and fertility improvement in North China larch plantations. Furthermore, it activates forest nutrient cycling, facilitating the rapid conversion of litter into nutrients that return to the soil, nourishing the plantations. This invention offers significant ecological benefits and has considerable application value. It provides a practical template for promoting litter decomposition enhancement technology in North China larch plantations.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions, or combinations of technical features in the above embodiments that do not conflict with each other, can be made in accordance with the manner described in the embodiments. These modifications, substitutions or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for promoting the decomposition of litter in larch plantations in North China, characterized in that, Includes the following steps: S1. Reduce canopy closure through differentiated thinning; S2. Clean and physically break up the larch litter layer in the thinning zone, and spread the broken litter in the cleared forest area and / or form a pile strip 0.5 meters away from the trees on both sides; S3. Artificial inoculation with biological agents and increased application of nitrogen fertilizer to accelerate the decomposition of litter; The artificial inoculation of biological agents includes inoculating the surface of the litter with a Trichoderma-Penicillium compound agent, injecting a compound agent-water-retaining agent into the middle layer, and spraying a chitosan solution at the bottom layer; the additional application of nitrogen fertilizer includes embedding slow-release nitrogen fertilizer in the surface of the litter, loading long-acting nitrogen in the middle layer, and spraying fast-acting nitrogen fertilizer at the bottom layer. The treatment method for the surface of fallen debris is as follows: Mix the compound microbial agent containing Trichoderma and Penicillium with forest humus and slow-release nitrogen fertilizer evenly, and apply it to the surface of fallen debris in the cleaned area within 24 hours after rain to increase the variety of microorganisms. The slow-release nitrogen fertilizer is sulfur-coated urea. The treatment method for the middle layer of litter is as follows: Starch-based water-retaining agent, straw fiber, starch binder, microbial spores, and urea-formaldehyde slow-release nitrogen fertilizer are made into cake-shaped slow-release blocks with a diameter of 10-20cm and a thickness of 3-7cm. The starch-based water-retaining agent, urea-formaldehyde slow-release nitrogen fertilizer, and microbial spores are wrapped in the inner layer of the cake-shaped slow-release blocks to obtain a microbial agent-water-retaining agent composite carrying long-acting nitrogen. The litter layer is dug into shallow pits 5-8cm deep, the microbial agent-water-retaining agent composite is placed in the pits, and then the fallen leaves are covered. The composites are arranged at fixed points at intervals of 3-5m in the litter accumulation zone, with 20-30 per acre. The treatment method for the bottom layer of litter is as follows: Ammonium nitrate is added to chitosan solution to prepare a composite solution with a nitrogen concentration of 2.5-3.5 g / L and a chitosan concentration of 0.8-1.2%; after inoculating the surface of litter with the composite microbial agent for 10-20 days, the composite solution is sprayed onto the surface of litter using a spraying device. The composite solution penetrates to the bottom layer of litter under the action of gravity; 50-80 L is sprayed per acre. S4. Targeted replanting of nitrogen-fixing shrubs and sowing of herbaceous plants to construct a diverse shrub-grass community; The measures for targeted replanting of nitrogen-fixing shrubs are as follows: In the rainy season of the second year after implementing step S3, transplant nitrogen-fixing shrub seedlings and plant them in a triangular layout with a spacing of 3-5m between plants / clumps and a density of 60-120 plants / clumps per hm². Dip the roots of the nitrogen-fixing shrubs in mud slurry with mycorrhizal fungi added. The measures for sowing herbaceous plants are as follows: every year from May to June, grass seeds are sown at the edge of the forest gaps at a rate of 4-6 kg / hm². After sowing, cover the gaps with shade netting that has a light transmittance of 38-42% to keep the soil moist and promote successful germination of the grass seeds.

2. The method according to claim 1, characterized in that, In S1, the differentiated thinning method is as follows: growth thinning is carried out on middle-aged / near-mature forests; Class V trees, Class IV trees and some Class III trees are removed to maintain the canopy closure at 60-65% and improve the light and heat environment under the forest.

3. The method according to claim 1, characterized in that, The steps of S2 are as follows: use a crusher to crush larch litter, and control the crushed particle size to 2-5cm; spread and pile the crushed litter in a 7:3 ratio, spread 70% of the crushed litter evenly in the cleaned area, and spread a loose layer with a thickness of 5-10cm; mix the remaining 30% of the crushed litter with the collected broadleaf tree leaves in a 1:1-2 ratio, and pile the mixture 0.5 meters away from both sides of the larch plant to form a compound pile strip 1-1.5m high and 10-20cm wide, with a spacing of 1-2m between the compound pile strips.

4. The method according to claim 3, characterized in that, The broad-leaved trees mentioned are mainly birch and / or aspen.

5. The method according to claim 1, characterized in that, In S3, the ratio of Trichoderma to Penicillium in the compound microbial agent is 2:1, and the viable count of the compound microbial agent is ≥5×10⁻⁶. 8 CFU / g; the humus soil is forest humus with a particle size of 2-5mm and a moisture content of 20-25%; the nitrogen slow-release period of sulfur-coated urea granules is 2 months, and the particle size is 1-2mm; the compound microbial agent, humus soil and slow-release nitrogen fertilizer are mixed evenly in a mass ratio of 1:10:2, and the application rate is 50-80kg / hm².

6. The method according to claim 1, characterized in that, In S3, when preparing the microbial agent-water-retaining agent complex carrying long-acting nitrogen, the nitrogen content of the urea-formaldehyde slow-release nitrogen fertilizer is 35-45%, and the amount of starch-based water-retaining agent is 25-40%; the microbial agent spores are a combination of white-rot fungi and actinomycetes.

7. The method according to claim 1, characterized in that, In S3, after placing the microbial agent-water-retaining agent complex carrying long-lasting nitrogen into the shallow pit and covering it with fallen leaves, add 30-50g of decomposed sheep manure around the microbial agent-water-retaining agent complex around each pit to construct a micro-environment of microorganisms-nitrogen fertilizer-organic matter.

8. The method according to claim 1, characterized in that, In S3, chitosan is dissolved in an aqueous acetic acid solution with a pH of 5.5-6.5, and ammonium nitrate and 0.1% Tween 80 are added to prepare a nitrogen-containing compound solution.

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