Method for promoting decomposition of litters in artificial forest of larix gmelini

Abstract

The invention relates to the technical field of forest management, in particular to a method for promoting decomposition of litters in an artificial forest of larch. The method comprises the following steps: S1, reducing canopy density through differential intermediate cutting; s2, cleaning and physically crushing the larch litter layer of the intermediate cutting zone, and spreading the crushed litter in a forest land cleaning zone and / or forming a stacking zone at the position 0.5 m away from the two sides of a plant; s3, artificially inoculating a biological agent and additionally applying a nitrogen fertilizer to accelerate the decomposition of litters; wherein the step of artificially inoculating the biological inoculant comprises the substeps of inoculating a trichoderma-penicillium complex inoculant on the surface layer of the litter, injecting an inoculant-water-retaining agent complex into the middle layer, and spraying a chitosan solution on the bottom layer; the step of increasing the nitrogen fertilizer comprises embedding a slow-release nitrogen fertilizer into the surface layer of the litter, loading a long-acting nitrogen element into the middle layer and spraying a quick-acting nitrogen fertilizer to the bottom layer; s4, nitrogen-fixing shrubs are directionally and complementarily planted, herbaceous plants are sown, and a multi-element shrub and grass community is constructed. The method disclosed by the invention has important significance on repairing the soil function of the artificial forest of the larch, fertilizing the soil, activating nutrient circulation, promoting renewal succession of the larch and realizing sustainable development of a forest ecological system.

Description

TECHNICAL FIELD

[0001] 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. BACKGROUND

[0002] Larix principis-rupprechtii is a unique tree species in the alpine coniferous forest zone in North China, and is the core force of land greening and ecological security barrier construction. It is widely distributed in the upper part of the mountains in Hebei, Shanxi and other provinces, and plays a key role in maintaining water and soil in high-altitude areas, conserving water resources, maintaining biodiversity, improving regional ecological environment, reducing wind and sand hazards, and regulating climate through dense canopy interception of precipitation and massive root network to hold soil. However, the current Larix principis-rupprechtii artificial forest is facing a significant imbalance in ecological function of litter. Influenced by the long-term pure forest management mode, the annual accumulation of litter under the forest is too large, with a thickness generally exceeding 10 cm, and the decomposition rate is very low, which is less than half of the decomposition rate of mixed coniferous and broad-leaved forest. The thick litter layer forms a dense physical barrier, hindering rainwater penetration and root respiration, resulting in a significant decrease in soil aeration and a compression of the effective activity space of microorganisms, which further leads to the stagnation of soil organic matter mineralization and the lack of available nutrients, and the overall soil fertility is significantly lower than that of mixed coniferous and broad-leaved forest, showing a clear trend of degradation. According to field investigations, the litter in Larix principis-rupprechtii artificial forest has the common characteristics of high cellulose, lignin and C / N ratio, small contact area with soil microorganisms due to thick accumulation, low soil microbial activity due to cold climate, and single type of litter.

[0003] The traditional method of mechanical ploughing causes the litter of Larix principis-rupprechtii to be buried in the soil, and the original soil layers are also broken, which destroys the surface humus layer (O layer) and soil aggregates, leading to a decrease in soil porosity, especially a decrease in aeration porosity, which seriously affects root respiration. Moreover, during the rainy season in the North China mountainous area, ploughing of forest land will exacerbate soil erosion. In addition, ploughing will bring deep anaerobic bacteria to the surface, while aerobic decomposing bacteria are buried in the deep layer, resulting in a decrease in litter decomposition rate and soil enzyme activity. Furthermore, mechanical ploughing has safety problems in slope operation, and the cost of labor and machinery is high, and the cost will double in the long term. SUMMARY

[0004] (I) Technical problems to be solved

[0005] In order to solve the problems of slow decomposition rate of litter, poor nutrient circulation and soil function decline in Larix principis-rupprechtii, the present application provides a method for promoting decomposition of litter in Larix principis-rupprechtii artificial forest, which realizes the paradigm shift of litter in Larix principis-rupprechtii artificial forest from "litter accumulation type degradation" to "nutrient circulation type health", and has important significance for repairing soil function in Larix principis-rupprechtii artificial forest, fertilizing soil, activating nutrient circulation, promoting Larix principis-rupprechtii regeneration succession, and realizing sustainable development of forest ecosystem.

[0006] (II) Technical Solution

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

[0008] S1. Reducing canopy density by differential thinning;

[0009] S2. Cleaning and physically breaking the larch litter layer in the thinning strip, and spreading the broken litter in the cleaned forest area and / or forming an accumulation strip 0.5 meters away from the plant on both sides;

[0010] S3. Artificially inoculating biological agents and increasing nitrogen fertilization to accelerate litter decomposition;

[0011] Wherein, the artificial inoculation of biological agents includes inoculating Trichoderma-Penicillium complex inoculant 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 increased nitrogen fertilization includes 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;

[0012] S4. Directional re-planting of nitrogen-fixing shrubs and sowing of herbaceous plants to construct a multi-element shrub-grass community.

[0013] According to the preferred embodiment of the present application, in S1, the differential thinning is: growth thinning is implemented on middle-aged forest / near-mature forest; V-class trees, IV-class trees and part of III-class trees are removed, so that the canopy density is maintained at 60-65%, and the light and heat conditions under the forest are improved.

[0014] Among them, V-class trees are dying trees / dying trees, characterized by a tree crown loss rate >75%, decayed branches or main stem, weak photosynthetic ability, and almost no growth potential as a source of pests and diseases. IV-class trees are suppressed trees, characterized by a tree crown being pressed by the upper layer (lateral branches being partially dead), an abnormal height-diameter ratio, growth stagnation, and a difficult-to-reverse competitive disadvantage. III-class trees are moderate trees, characterized by a tree crown integrity of 60-80%, being pressed by a certain side but still having growth space. Selective removal of III-class trees only thins III-class trees in the over-dense area, and individuals with good stem shape are reserved as backup target trees.

[0015] By differential thinning to reduce canopy density, the following effects can be achieved: ① reducing stand density directly reduces the annual accumulation of litter; ② improving water and heat conditions under the forest and increasing light intensity under the forest, which not only provides basic light conditions and growth space for the planting of shrubs and grasses; ③ increasing the types of litter, increasing light, and alleviating the inhibitory effect of lower air temperature in high-altitude areas on microorganisms.

[0016] According to the preferred embodiment of the present application, the step S2 is: using a pulverizer to crush the larch litter, and controlling the crushing particle size to be 2-5 cm; the crushed litter is treated by spreading and stacking in a ratio of 7:3, 70% of the crushed litter is evenly spread in the cleaning area with a loose layer of 5-10 cm in thickness; the remaining 30% of the crushed litter is mixed with the collected broadleaf tree litter in a ratio of 1:1-2, and after mixing, the mixture is stacked on both sides of the larch plant 0.5 meters away to form a 1-1.5 m high and 10-20 cm high compound stacking zone, and the distance between the compound stacking zones is 1-2 m.

[0017] The pulverizer is a disc harrow pulverizer; when the litter is crushed, the surface layer (5-10 cm thick) of the litter layer with a thickness of >15 cm in the forest gap and the thinning belt is crushed. The broadleaf trees are mainly white birch (birch C / N≈23) and aspen. The broadleaf tree litter has a low carbon content (low C / N ratio), and the compound of the broadleaf tree litter and the crushed larch litter reduces the C / N ratio of the larch litter from 80:1 to below 50:1, thereby creating a low carbon-nitrogen ratio environment for the subsequent inoculation of biological agents.

[0018] The C / N ratio of the larch litter is high, and the microorganism decomposition needs to maintain a metabolic balance of C / N≈24, so when nitrogen is deficient, the microorganism needs to fix nitrogen from the soil, and the microorganism is enriched in the soil, which leads to a significant decrease in the decomposition efficiency of the litter. In addition, the larch litter has a high lignin content (15-25%), and the microorganism needs to consume more energy to synthesize lignin-degrading enzymes (such as laccase and peroxidase), which leads to low microbial activity and limited growth and reproduction.

[0019] The cleaning and physical crushing of the litter can break the physical barrier of the litter, and the effects include: ①reducing the coverage and suppression of the litter on the shrub and grass seedlings, and improving the seedling emergence rate, survival rate and natural regeneration success rate of the shrub and grass seedlings; ②optimizing the physical structure of the litter decomposition through crushing and cleaning, significantly increasing the specific surface area of the litter, exposing more cellulose and lignin sites, and improving the contact efficiency of the microorganism (the larch needle surface contains hydrophobic wax and terpene resin, which hinders water penetration and enzyme contact, prolongs the softening period, and delays the decomposition start); ③the natural decomposition of the stacking zone and the synergistic effect with the biological agent inoculated later produce a large amount of humus, which provides sustained nutrient supply for the growth of shrubs and grasses.

[0020] According to the preferred embodiment of the present application, in S3, the treatment method for the surface layer of the litter is to mix the compound microbial agent containing Trichoderma and Penicillium, undergrowth humus soil and slow-release nitrogen fertilizer uniformly, and to apply it on the surface layer of the cleaned area within 24 hours after the rain to increase the types of microorganisms, and the slow-release nitrogen fertilizer is sulfur-coated urea; the nitrogen fertilizer provides nitrogen source for the microorganisms, promotes the rapid colonization of Trichoderma-Penicillium, and at the same time, the sulfur-coated urea slowly releases nitrogen (peak period of release is from June to August), which is synchronized with the decomposition peak period of the microbial agent.

[0021] The treatment method for the middle layer of the litter is to make a cake-shaped slow-release block with a diameter of 10-20 cm and a thickness of 3-7 cm (preferably a diameter of 10-15 cm and a thickness of 3-5 cm) by using the starch-based water-retaining agent, straw fiber, starch adhesive, microbial agent spores and urea-formaldehyde slow-release nitrogen fertilizer, to wrap the starch-based water-retaining agent, urea-formaldehyde slow-release nitrogen fertilizer and microbial agent spores in the inner layer of the cake-shaped slow-release block, and to obtain the microbial agent-water-retaining agent composite carrying long-acting nitrogen; to dig shallow pits with a depth of 5-8 cm in the litter layer, to put the microbial agent-water-retaining agent composite into the pits, to cover the litter, and to arrange the pits at intervals of 3-5 m in the litter accumulation zone, and to arrange 20-30 pits per mu.

[0022] The treatment method for the bottom layer of the litter is to add ammonium nitrate into a chitosan solution to obtain a composite solution with a nitrogen concentration of 2.5-3.5 g / L and a chitosan concentration of 0.8-1.2%; to spray the composite solution on the surface layer of the litter using a spraying device after 10-20 days of inoculation of the compound microbial agent on the surface layer of the litter, and to penetrate the composite solution to the bottom layer of the litter under the action of gravity; and to spray 50-80 L per mu.

[0023] According to the preferred embodiment of the present application, in S3, the ratio of Trichoderma to Penicillium in the compound microbial agent is 2:1, the number of viable bacteria in the compound microbial agent is greater than or equal to 5 x 10 8 CFU / g; the humus soil is undergrowth humus with a particle size of 2-5 mm and a water content of 20-25%; and the sulfur-coated urea granules have a nitrogen slow-release period of 2 months and a particle size of 1-2 mm. Among them, the compound microbial agent, the humus soil and the slow-release nitrogen fertilizer are uniformly mixed at a mass ratio of 1:10:2, and the application amount is 50-80 kg / hm 2 .

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

[0025] According to the preferred embodiment of the present application, in S3, after the bacteria agent-water retaining agent complex carrying long-acting nitrogen is placed in the shallow pit, the pit is covered with fallen leaves, and 30-50 g of decomposed sheep manure is added around the bacteria agent-water retaining agent complex to construct a microenvironment of microorganisms-nitrogen fertilizer-organic matter around each pit.

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

[0027] In view of the problems of high cellulose and lignin content of the litter of the Larix principis-rupprechtii plantation in North China, poor soil microbial activity, and poor diversity, the step S3 of the present application combines inoculation of biological bacteria agent and increased nitrogen fertilizer, the surface is inoculated with a composite bacteria agent and slow-release nitrogen fertilizer, Trichoderma-penicillium rapidly colonizes the litter, the middle layer is embedded with a bacteria agent-water retaining agent complex carrying long-acting nitrogen, and the nitrogen and microorganisms are locally enriched to continuously supply active microorganisms to the surrounding litter; the bottom layer is sprayed with a chitosan solution and quick-acting nitrogen fertilizer to activate the proliferation of indigenous microorganisms, and the amount of soil microorganisms is increased.

[0028] According to the preferred embodiment of the present application, in S4, the measure of directional re-planting of nitrogen-fixing shrubs is that, in the second year of the rainy season after the implementation of step S3, nitrogen-fixing shrub seedlings are transplanted, and are planted in a triangular shape with a spacing of 3-5 m between plants / bushes and a density of 300-500 plants / bushes per hm 2 60-120 plants / bushes are planted, and the roots of the nitrogen-fixing shrubs are dipped in a mud slurry to which a mycorrhizal fungus agent is added to improve the survival rate. The nitrogen-fixing shrub seedlings are lilac or hu zhi zi, and the amount of the mycorrhizal fungus agent added to the mud slurry is 0.5-2 wt%, preferably 1 wt%;

[0029] The measure of sowing herbaceous plants in the forest gap is that, in May-June each year, herb seeds are sown on the edge of the forest gap, and the sowing amount of the herb seeds is 4-6 kg / hm 2After sowing, cover the shading net with light transmittance of 38-42% to keep the forest gap soil moist and make the grass seeds germinate smoothly. Among them, the grass seeds are preferably sedge, clematis and the like, which are suitable for the climate of the Larix principis-rupprechtii artificial forest in North China, have good shade tolerance, low photosynthetic compensation point, and more importantly, the leaf C / N ratio of the grass is moderate (25-30), the litter decomposition rate is fast, and the nitrogen turnover in the forest gap can be accelerated, and the roots of the grass can also secrete organic acid to activate soil phosphorus, and alleviate the soil infertility caused by long-term continuous cropping of the artificial forest.

[0030] (III) Beneficial effects

[0031] The scheme of the present application solves the problem of slow litter decomposition in the Larix principis-rupprechtii artificial forest by optimizing stand structure, removing and crushing litter, inoculating biological inoculants and increasing nitrogen fertilizer and the like. Compared with the traditional mechanical ploughing method, the method of the present application causes less damage to the soil structure and indigenous microorganisms of the stand, has lower requirements for machinery, is helpful for protecting the original soil levels and soil microbial community, and makes the decomposition promotion measures concentrated in the target area through in-forest spreading and stacking in a regional manner, so as to avoid ecological disturbance caused by intervention in the whole forest.

[0032] In the scheme of the present application, the initial decomposition rate of the litter is obviously improved through the crushing treatment of the litter, and the litter thickness is obviously reduced within 1 year in cooperation with the inoculants and increased nitrogen fertilizer. Under the synergistic action of crushing and compound inoculants, the degradation rates of cellulose and lignin are significantly higher than the effect of single inoculant treatment.

[0033] The traditional method is to inoculate the inoculants on the surface layer of the litter to promote the decomposition of the litter. Although the method can increase the types of microorganisms and improve the decomposition rate of the litter, the activity of the microbial inoculants is poor in the middle and bottom layers of the litter, which leads to insufficient decomposition rate of the litter. The multi-level and all-round biological inoculant inoculation method adopted in the method of the present application, that is, the surface layer is inoculated with compound inoculants, the middle layer is buried with long-acting nitrogen, the bottom layer is activated with chitosan and quick-acting nitrogen, can not only effectively increase the types of microorganisms, but also stimulate the proliferation of indigenous microorganisms, so that the efficiency of promoting the decomposition of the litter in the present scheme is more significant.

[0034] The traditional litter surface inoculation agent method can only play a short-term role, and it is difficult to fundamentally solve the problem of slow decomposition of litter in the Larix principis-rupprechtii plantation in North China, and form a benign dynamic self-circulation, and the multi-level biological community structure of combining arbor, shrub and herbaceous plant, and mixing coniferous and broad-leaved trees is the fundamental way to realize efficient decomposition of litter, accelerate material circulation and maintain ecological balance of forest land. Therefore, the present application proposes a four-dimensional technical system of "physical crushing resistance reduction - slow long-term nitrogen fertilizer layered application - biological microbial population catalysis - plant community cooperation", which significantly improves the decomposition efficiency of litter under the premise of ensuring ecological friendliness, effectively promotes the repair of soil function and the improvement of soil fertility in the Larix principis-rupprechtii plantation in North China, and further activates the nutrient cycle of forest land, and has good ecological benefits and application value. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The block diagram of the method for promoting the decomposition of litter in the Larix principis-rupprechtii plantation.

[0036] Figure 2 The schematic diagram of constructing a multi-element shrub and grass community in the method of the present application.

[0037] Figure 3 The position schematic diagram of the accumulation zone after the litter is cleaned and crushed in the method of the present application. DETAILED DESCRIPTION

[0038] In order to better explain the present application, so as to be understood, the present application is described in detail by specific embodiments in combination with the drawings.

[0039] After years of research, it is confirmed that the main reasons for slow decomposition of litter in the Larix principis-rupprechtii plantation are as follows: first, the stand density is too high, and the shrubs and grasses under the forest are few, which leads to thick and single type of litter accumulation, especially the pure forest is much thicker than the mixed forest. At the same time, the thick accumulation of litter leads to small contact area with soil microorganisms, and slow start of litter decomposition. Second, Larix principis-rupprechtii belongs to coniferous trees, and the cellulose, lignin and C / N of litter are high, and the surface litter is acidic, which leads to poor soil microbial diversity and underdeveloped microbial community. Third, the climate in high altitude area is cold, which seriously limits the activity and activity time of microorganisms that decompose litter, and the decomposition efficiency is low, and a large amount of litter accumulates for many years.

[0040] In order to solve the technical problems of slow decomposition of litter in larch plantations, difficulty in quickly returning litter nutrients to the soil, slow nutrient circulation in plantations, and significantly lower comprehensive soil fertility than in mixed forests, the present invention proposes a method for promoting litter decomposition in larch plantations. The method optimizes the forest stand structure through differentiated thinning, targeted shrub-grass replanting, constructs a diversified community, increases the variety of litter in larch plantations, and improves the decomposition rate of litter; and crushes and piles the litter in layers to create a good growth space for shrubs and grasses. In a compound manner, corresponding measures are taken in layers from the surface layer to the middle layer to the deep layer of the litter, including the introduction of biological agents and the application of additional nitrogen fertilizers, the adjustment of the carbon-nitrogen ratio of the litter, the increase of the variety of microorganisms in the litter, the improvement of microbial activity, and the maintenance of the sustainability of microbial activity. Then, with the help of the self-regulating and repairing ability of the ecosystem, the activity of indigenous microorganisms is stimulated and the proliferation of indigenous vitamins is promoted, thereby achieving a paradigm shift from "litter accumulation-type degradation" of larch plantations to "nutrient recycling-type health". The invention has important significance for promoting the return of nutrients contained in fallen leaves to the soil, repairing the soil function of Larix principis-rupprechtii plantations, fertilizing the soil, activating nutrient circulation, promoting the regeneration and succession of Larix principis-rupprechtii, and realizing the sustainable development of forest ecosystems.

[0041] The following describes the preferred embodiments of the present invention.

[0042] Example 1

[0043] like Figure 1 As shown, this embodiment provides a method for promoting the decomposition of litter in a Larix principis-rupprechtii plantation, which includes the following steps 1 to 4:

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

[0045] (1) Implement growth felling in middle-aged forests / near-mature forests, remove Class V trees, Class IV trees and some Class III trees (poorly growing individuals), maintain a canopy density of 60-65%, and improve the water and heat conditions under the forest.

[0046] Through the above-mentioned differentiated thinning, the forest stand density is reduced, the annual accumulation of litter is directly reduced, the water and heat conditions under the forest are improved, and the light intensity under the forest is increased. This not only provides basic light conditions and growth space for the establishment of shrubs and grasses, but also increases the types of litter and increases sunshine, which to a certain extent alleviates the inhibitory effect of low temperature on microbial activity in high-altitude areas.

[0047] Step 2: Clean and physically break up the larch litter layer in the thinning zone, and spread the broken litter in the cleared area and / or form a pile 0.5 meters on both sides of the plants. Specific measures are as follows:

[0048] For the forest gap and the litter layer with a thickness of > 15 cm, first use a disc harrow pulverizer to break it up, and control the particle size of the litter to 2-5 cm. Then, treat the broken litter according to the ratio of "70% scattering + 30% stacking": scatter 70% of the broken litter evenly on the cleaned area to form a loose layer with a thickness of 5-10 cm, and accelerate decomposition through the fresh wounds generated by breaking to start the process. Mix the remaining 30% of the broken litter with the collected birch and poplar broadleaf tree leaves at a ratio of 1:1, and stack them on both sides of the plants 50 cm away to form a complex stacking zone with a width of 1-1.5 m and a height of 10-20 cm, with a spacing of 1-2 m. Figure 3 After compounding, the C / N ratio of the litter is reduced from 80:1 to below 50:1, creating a low carbon-nitrogen ratio environment for subsequent inoculation of microbial agents.

[0049] By cleaning and physically breaking up the litter, the physical barriers of the litter can be broken down. On the one hand, it can reduce the coverage and suppression of shrub and grass seedlings by the litter, and improve the seedling emergence rate, survival rate, and natural regeneration success rate of the shrubs and grasses. On the other hand, through pulverization and cleaning, the physical structure of litter decomposition can be optimized, the specific surface area of the litter is significantly increased, more cellulose and lignin sites are exposed, and the contact efficiency of microorganisms is improved. In addition, the natural decomposition of the stacking zone and the synergistic effect with the bio-inoculant inoculated later produce a large amount of humus, providing a continuous nutrient supply for the growth of shrubs and grasses.

[0050] Step three: artificial inoculation of bio-inoculants and increased nitrogen fertilization to accelerate litter decomposition.

[0051] Among them, artificial inoculation of bio-inoculants includes inoculating Trichoderma-penicillium complex inoculants on the surface layer of the litter, injecting inoculant-water retaining agent complex in the middle layer, and spraying chitosan solution in the bottom layer; increased nitrogen fertilization includes embedding slow-release nitrogen fertilizer in the surface layer of the litter, loading long-acting nitrogen in the middle layer, and spraying quick-acting nitrogen fertilizer in the bottom layer. The specific measures are as follows:

[0052] (1) Embedding slow-release nitrogen fertilizer in the surface layer

[0053] Mix Trichoderma and Penicillium at a ratio of 2:1 to obtain a complex inoculant with a viable bacterial count of ≥5x10 8 CFU / g. Mix the complex inoculant, humus soil with a particle size of 2-5 mm (moisture content 20%), and sulfur-coated urea granules (containing 30% nitrogen, 0% phosphorus and potassium, particle size 1-2 mm, slow-release period 2 months) at a ratio of 1:10:2 to obtain a compounded material. The compounded material is uniformly applied on the surface of the litter in the cleaned area within 24 hours after rain to increase the types of microorganisms, with an application amount of 50-80 kg / hm 2 . Nitrogen fertilizer provides nitrogen source for microorganisms, promoting the rapid colonization of Trichoderma-penicillium, while sulfur-coated urea slowly releases nitrogen (peak release period from June to August), which is synchronized with the decomposition peak period of the inoculant.

[0054] (2) Middle layer buried cake-shaped slow-release block containing long-acting nitrogen + microbial agent + water-retaining agent

[0055] Straw fiber and starch adhesive are used as a wrapping layer, and microbial agent spores, starch-based water-retaining agent, and urea-formaldehyde slow-release nitrogen fertilizer (nitrogen content 40%) are wrapped in the inner layer to produce a cake-shaped slow-release block with a diameter of about 10 cm and a thickness of 3 cm. A shallow pit 5-8 cm deep is dug in the litter layer, and the cake-shaped slow-release block is placed in the pit and covered with fallen leaves. The cake-shaped slow-release block is arranged in the litter accumulation zone at an interval of 3-5 m, with 20-30 blocks per mu. When covering the fallen leaves, 50 g of decomposed sheep manure (C / N = 10:1) is added around the cake-shaped slow-release block to form a "microbial-nitrogen-organic matter" microzone, promoting the local enrichment of nitrogen (total nitrogen contribution about 35-60 kg / hm 2 ).

[0056] The inner layer accounts for about 75% (nitrogen fertilizer accounts for 15%, starch-based water-retaining agent accounts for 30%, and the rest is microbial agent spores), and straw fiber and starch adhesive account for about 25%. The microbial agent spores are a combination of white rot fungi (such as Phanerochaete chrysosporium) and actinomycetes. The starch adhesive is an environmentally friendly adhesive made from natural starch as the main raw material through physical, chemical, or enzymatic modification. It is biodegradable and non-toxic. The starch-based water-retaining agent can absorb 300-500 times its own weight of water, forming a local high-humidity microzone (humidity > 65%) around the cake-shaped slow-release block, maintaining continuous microbial activity (white rot fungi require humidity > 55% to secrete ligninase), and solving the problem of litter decomposition stagnation caused by drought in North China. The starch-based water-retaining agent itself contains soluble polysaccharides (such as dextrin), which can be used as an auxiliary carbon source for microorganisms, and cooperates with urea-formaldehyde slow-release nitrogen fertilizer (C / N ≈ 8:1) to regulate the microzone C / N ratio to the ideal decomposition threshold of 25-30.

[0057] (3) Bottom layer sprayed with chitosan and quick-acting nitrogen to activate bottom soil microorganisms to proliferate

[0058] Chitosan is dissolved in a dilute acetic acid aqueous solution with a pH of 5.5-6.5, and Tween 80 (to enhance the permeability of the solution) is added to obtain a chitosan solution. Ammonium nitrate is added to the chitosan solution to prepare a compound solution with an ammonium nitrate concentration of 3 g / L and a chitosan concentration of 1%. The compound solution is uniformly sprayed on the surface of the fallen larch litter, with 50-80 L sprayed per mu, which can contribute about 15-24 kg / hm 2 of pure nitrogen. The compound solution penetrates into the bottom layer of the litter (penetrates 8-10 cm downward) by gravity to stimulate the proliferation of indigenous microorganisms, increasing the amount of soil microorganisms.

[0059] Chitosan is a dual-effect agent that induces resistance signals and acts as an antibacterial and growth-promoting agent: chitosan decomposition products (such as chitosan oligosaccharides) act as quorum sensing molecules for microorganisms, stimulating indigenous actinomycetes (such as Streptomyces) and white rot fungi (such as Trametes) to secrete lignin-degrading enzymes (laccase, manganese peroxidase). Chitosan can also inhibit pathogens (such as Fusarium) in litter, while promoting the colonization of beneficial bacteria (such as Pseudomonas). Chitosan forms a semi-permeable membrane on the surface of litter, regulating the water permeation rate, preventing the rapid loss of ammonium nitrate, and maintaining air permeability. Ammonium nitrate provides fast-acting NH4 + and NO3 - , reducing the C / N ratio 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 high-efficiency decomposition bacteria, the decomposition rate of cellulose and lignin is significantly improved, and a symbiotic environment is provided for indigenous microorganisms, thereby increasing microbial diversity; ② The comprehensive application of composite bacterial agents, humus soil, water-retaining agents and chitosan from top to bottom forms a three-dimensional carbon and nitrogen regulation and decomposition promotion network of "upper layer inoculation-middle layer slow release-bottom layer activation", which effectively reduces the C / N ratio in litter and improves the efficiency of litter decomposition; by increasing the application of slow-release-long-acting-fast-acting nitrogen fertilizers, the change trend of the carbon-nitrogen ratio (C / N) is more in line with the metabolic activity cycle of the bacterial agents, maintaining the sustainability of microbial vitality and improving the microbial decomposition rate; ④ Coupling is achieved through the microbial-nutrient cycle, producing a synergistic effect and improving the decomposition rate.

[0061] Step 4: Targeted planting of nitrogen-fixing shrubs and sowing of herbaceous plants to build a diverse shrub-grass community. Specific measures are as follows:

[0062] In the rainy season (July-August) of the second year after thinning, shrub seedlings such as lilac and Lespedeza are transplanted in a "pink-shaped" layout with a spacing of 3-5m between plants (clusters) and a density of 60-120 plants (clusters) / hm2. 2 , dip the roots in mud, add 1% mycorrhizal fungi agent to the mud to improve the survival rate. In May and June each year, sow grass seeds such as moss and thrush at the edge of the forest window, with a sowing rate of 5kg / hm 2 , cover with a sunshade net with a light transmittance of 40%, and keep the soil moist until the seedlings emerge (such as Figure 2 shown).

[0063] Mycorrhizal fungi agents are biological preparations made from the spores, mycelium or propagules of mycorrhizal fungi. They are used to artificially inoculate plant roots to form a mycorrhizal symbiosis. This symbiotic relationship can significantly improve the plant's efficiency in absorbing water and nutrients and enhance its resistance to stress.

[0064] Application Example 1

[0065] The application is applied to the Larix principis-rupprechtii artificial forest in Jinguotun Forest Farm of Luanping State-owned Forest Farm in Chengde City of Hebei Province and Wangxidong Forest Farm of Xiaowutaishan National Nature Reserve in Hebei Province.

[0066] I. Test site overview

[0067] Test site of Jinguotun Forest Farm of Luanping State-owned Forest Farm: Chahe River Basin in Luanping County of Hebei Province, concentrated distribution area of Larix principis-rupprechtii artificial forest; age 43 years, pure forest canopy density 0.85, 1073 trees per 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] Test site of Wangxidong Forest Farm of Xiaowutaishan National Nature Reserve: Xiaowutaishan National Nature Reserve in Hebei Province, subalpine coniferous forest belt; age 48 years, pure forest canopy density 0.90, 1575 trees per hectare, average diameter at breast height 14.4 cm, litter thickness 20-25 cm, C / N ratio 90:1, understory shrub and grass coverage 5.6%; microbial activity period <5 months, significantly stressed by low temperature.

[0069] II. Test design

[0070] At the test site of Jinguotun Forest Farm and the test site of Wangxidong Forest Farm, treatment groups (T) are set up to implement the measures of "differentiated thinning + shrub and grass re-planting + litter crushing and cleaning + inoculation of microbial agents + nitrogen fertilizer regulation", with an area of 8 mu, numbered as Jinguotun T group and Wangxidong T group; the control group (CK) does not intervene in litter decomposition, numbered as Jinguotun CK group and Wangxidong CK group. After the measures are taken, the litter thickness, humus layer thickness, litter accumulation, organic matter content and total nitrogen content of the topsoil layer (0-20 cm) of the treatment group and the control group are measured. After 3 years of taking measures, the relevant indicators are measured again.

[0071] III. Implementation

[0072] 1. Differentiated thinning (May 2020)

[0073] In the area with canopy density >80%, thinning is implemented to reduce the canopy density to 60%.

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

[0075] Use a disc harrow to crush the surface litter, and then clean the crushed litter for use. Spread 70% of the crushed litter evenly in the cleaned area between the Larix principis-rupprechtii rows to form a loose layer with a width of 3-4 m and a thickness of 5-8 cm; mix the remaining 30% of the crushed litter with the collected birch leaves at a ratio of 1:1, and pile them on both sides of the plants 50 cm away, with a width of 1.2 m and a height of 10-20 cm, and the pile spacing is 2 m, which reduces the local C / N ratio of the litter to below 50:1.

[0076] 3. Bioinoculant inoculation and nitrogen fertilizer regulation (July-August 2020)

[0077] Litter surface layer: Inoculate with complex microbial inoculant + slow-release nitrogen fertilizer. Mix 1 part of Trichoderma-penicillium complex microbial inoculant + 10 parts of humus soil + 2 parts of sulfur-coated urea granules (nitrogen-phosphorus-potassium = 30-0-0) to obtain a compound, and evenly apply it to the surface layer of the litter cleaning area and the accumulation zone within 24 hours after the rain, with a spreading amount of 50 kg / hm 2 .

[0078] Litter middle layer: While inoculating the complex microbial inoculant on the surface layer, a 5-8 cm deep shallow pit is dug in the litter layer, and a 10 cm diameter, 3 cm thick cake-shaped slow-release block is placed at intervals of 3 m, and then the fallen leaves are covered. The outer layer of the cake-shaped slow-release block is straw fiber + starch adhesive, and the inner layer is white rot fungus + actinomycetes + starch-based water retaining agent + urea-formaldehyde slow-release nitrogen fertilizer, 24 blocks per mu. When covering the fallen leaves, add 50 g of decomposed sheep manure around the cake-shaped slow-release block. The nitrogen fertilizer in the cake-shaped slow-release block accounts for 15%, the starch-based water retaining agent accounts for 30%, the straw fiber and starch adhesive account for about 25%, and the rest is microbial inoculant spores.

[0079] Litter bottom layer: A composite solution is prepared according to the mass ratio of chitosan: Tween 80: ammonium nitrate: water = 10:1:8.8:980.2, and the composite solution is sprayed onto the surface of the litter, with a uniform spraying amount of 50 L per mu. The composite solution penetrates to the bottom layer of the litter under gravity.

[0080] 4. Supplemental planting of shrubs and grasses (May-August 2021)

[0081] Planting lilac, hu zhi zi, and caragana on the edge of the forest gap, with a plant spacing of 3 m, and 60 plants per hm 2 Dip the roots in mud slurry with the addition of 1% mycorrhizal fungal inoculant; additionally, sow 5 kg / hm of moss and meadowrue seeds on the edge of each forest gap 2 .

[0082] IV. Test results

[0083] The test results are shown in Tables 1 and 2. The litter thickness and litter accumulation of the treatment group with litter acceleration measures were significantly lower than those of CK, indicating that the measures of "differentiated thinning + litter crushing and cleaning + microbial inoculation + nitrogen fertilizer regulation + supplemental planting of shrubs and grasses" significantly improved the decomposition rate of litter; at the same time, the humus layer thickness, organic matter content and total nitrogen content of the treatment group were significantly increased compared with CK, indicating that this method also increased the humus layer thickness and soil nutrient content of the Larix principis-rupprechtii plantation in North China.

[0084] Table 1 Test results at the Jindoutun test site

[0085]

[0086] Table 2 Test results of Wangxidong forest test site

[0087]

[0088] Through the contrast test of different altitudinal gradients in Luanping and Xiaowutaishan, it can be proved that the scheme of the present application has practical applicability under different site conditions, not only can greatly reduce the litter thickness and reduce the litter accumulation of the CK group, but also can effectively increase the thickness of the humus layer, improve the content of organic matter and nitrogen in the surface soil layer, significantly improve the decomposition efficiency of litter under the premise of ensuring ecological friendliness, effectively promote the repair of soil function and the improvement of soil fertility of the Larix principis-rupprechtii artificial forest, further activate the nutrient cycle of the forest land, promote the litter to become nutrients and return to the soil quickly, nourish the artificial forest, and have good ecological benefits and popularization and application value. The present application provides a practical template for the promotion of the litter decomposition promotion technology of the Larix principis-rupprechtii artificial forest.

[0089] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements, or in the case of no conflict between the technical features in the above embodiments, can be combined in the manner recorded in the embodiments, and these modifications, replacements or combinations do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for promoting the decomposition of litter in a Larix principis-rupprechtii plantation, characterized in that: The steps include: S1. Reduce canopy density through differentiated thinning; S2. Clear and physically break up the larch litter layer in the thinning zone, spreading the broken litter in the cleared area and / or forming a pile 0.5 m on either side of the trees; S3. Artificial inoculation of biological agents and application of nitrogen fertilizers to accelerate the decomposition of litter; The artificial inoculation of biological agents includes inoculating a Trichoderma-Penicillium composite agent on the surface of the litter, injecting a bacterial agent-water retaining agent complex into the middle layer, and spraying a chitosan solution on the bottom layer; the nitrogen fertilizer application includes embedding a slow-release nitrogen fertilizer into the surface of the litter, loading a long-acting nitrogen into the middle layer, and spraying a quick-acting nitrogen fertilizer on the bottom layer; S4. Directed planting of nitrogen-fixing shrubs and sowing of herbaceous plants to build a diverse shrub-grass community.

2. The method according to claim 1, characterized in that In S1, the differentiated thinning method is: growth felling is carried out on middle-aged forests / near-mature forests; Class V trees, Class IV trees and some Class III trees are felled to keep the canopy density 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: use a crusher to crush the larch litter, and control the crushed particle size to 2-5 cm; spread and pile the crushed litter in a ratio of 7:3, and evenly spread 70% of the crushed litter in the cleaned area to form a loose layer with a thickness of 5-10 cm; mix the remaining 30% of the crushed litter with the collected broad-leaved tree fallen leaves in a ratio of 1:1-2, and pile them 0.5 meters away from both sides of the larch plant to form a 1-1.5m and 10-20cm high compound pile belt, and the spacing between the compound pile belts is 1-2m.

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

5. The method according to claim 1, wherein In S3, the treatment method for the surface of litter is: a composite agent containing Trichoderma and Penicillium is mixed evenly with understory humus soil and slow-release nitrogen fertilizer, and applied to the surface of 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 middle layer of litter is treated as follows: a starch-based water-retaining agent, straw fiber, starch adhesive, bacterial spores, and urea-formaldehyde slow-release nitrogen fertilizer are combined into cake-shaped slow-release blocks with a diameter of 10-20 cm and a thickness of 3-7 cm. The starch-based water-retaining agent, urea-formaldehyde slow-release nitrogen fertilizer, and bacterial spores are then wrapped in the inner layer of the cake-shaped slow-release blocks to produce a bacterial agent-water-retaining agent complex that carries long-lasting nitrogen. Shallow pits 5-8 cm deep are dug in the litter layer, and the bacterial agent-water-retaining agent complex is placed in the pits, covered with fallen leaves, and placed at fixed points in the litter accumulation zone at intervals of 3-5 m, with 20-30 blocks per mu. The method for treating the bottom layer of litter is as follows: ammonium nitrate is added to the 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%; 10-20 days after the composite bacterial agent is inoculated on the surface of the litter, the composite solution is sprayed on the surface of the litter using a spraying device, and the composite solution penetrates into the bottom layer of the litter under the action of gravity; 50-80 L is sprayed per mu.

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

7. The method according to claim 5, characterized in that In S3, when preparing the bacterial agent-water retaining agent complex carrying long-term nitrogen, the nitrogen content of the urea formaldehyde slow-release nitrogen fertilizer is 35-45%, and the amount of the starch-based water retaining agent is 25-40%; the bacterial agent spores are a combination of white rot fungi and actinomycetes.

8. The method according to claim 5, characterized in that In S3, after placing a microbial agent-water retaining agent complex carrying long-acting nitrogen in a shallow pit and covering it with fallen leaves, 30-50g of decomposed sheep manure was added around the microbial agent-water retaining agent complex around each pit to construct a micro-environment of microorganisms-nitrogen fertilizer-organic matter.

9. The method according to claim 5, characterized in that In S3, chitosan is dissolved in an acetic acid aqueous solution with a pH of 5.5-6.5, and ammonium nitrate and 0.1% Tween 80 are added to prepare a nitrogen fertilizer-containing composite solution.

10. The method according to claim 1, characterized in that In S4, the measures for targeted replanting of nitrogen-fixing shrubs are: in the rainy season of the second year after the implementation of step S3, transplant nitrogen-fixing shrub seedlings and plant them in a herringbone pattern with a spacing of 3-5m between plants / clumps and a density of 1000 sq. m per hm2. 2 Plant 60-120 plants / clump, and dip the roots of nitrogen-fixing shrubs into mud with mycorrhizal fungi added; The measures for sowing herbaceous plants are: sowing grass seeds at the edge of forest gaps from May to June each year, with a sowing rate of 4-6 kg / hm 2 After sowing, cover with a shade net with a light transmittance of 38-42% to keep the soil in the forest window moist so that the grass seeds can germinate smoothly.

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