Analysis of decomposition rate and key influencing factors of larch leaf litter regeneration in different types of burned areas

Abstract

The present invention discloses an analysis method for the decomposition rate and key influencing factors of larch leaf litter regeneration in different types of burned areas, which specifically includes the following steps: S1, analyzing the stand and environmental characteristics of larch forests regenerated in different types of burned areas; S2, analyzing the leaf litter characteristics of larch forests regenerated in different types of burned areas; S3, analyzing the leaf litter decomposition characteristics and main influencing factors of larch forests regenerated in different types of burned areas. The present invention takes larch forests in different types of burned areas as the research object, investigates and analyzes the biological and abiotic factors of various sites, clarifies the dynamic characteristics of larch community construction under different fire intensities and recovery times, and reveals the response strategies adopted by the leaf traits of regenerated larch to adapt to environmental changes; identifies the main difference indicators of larch leaf litter traits in different types of burned areas, and reveals the direct or indirect influence mechanism of various factors on the decomposition of larch leaf litter, which is of great significance for accurately estimating the nutrient supply of larch forests in burned areas.

Description

Technical Field

[0001] The invention relates to the technical field of forest cultivation, and in particular to an analysis method of decomposition rates of larch litter leaves for regeneration of different types of burned sites and key influencing factors. Background Art

[0002] The litter layer is an important nutrient pool and source of soil organic matter for the ecological succession and biogeochemical cycle of boreal forests. Affected by the cold temperate monsoon climate, forest fires frequently occur in the Greater Khingan Range, which is a high-incidence area of ​​fires. The consumption of litter layers by forest fires and the disturbance of forest stand structure have aroused people's attention to the long-term productivity maintenance mechanism of larch in the process of community succession in burned areas. Therefore, it is of great significance to study the decomposition of larch litter in burned areas.

[0003] Leaves are the main photosynthetic organs of plants, which are closely related to the carbon assimilation and resource utilization capabilities of plants. They can directly reflect the survival strategies adopted by plants to adapt to environmental changes and directly affect the characteristics of leaf litter. Leaf litter traits affect biomass degradation by regulating soil microbial biomass and enzyme activity. Most of the effects of litter matrix on decomposition rate focus on the differences in different litter compositions. Current studies have found that forest fires have caused significant and long-term disturbances to community vegetation types and soil resource availability. At the whole plant level, resource acquisition strategies among species are broadly consistent, but at the intraspecific level, plants also show partially decoupled and finely tuned strategies to respond to environmental changes. This decoupling within species suggests that many species-centered ecological theories are needed to study how plants respond to the environment. Understanding the effects of forest fire disturbance on larch leaf traits and leaf litter decomposition can help us to gain a deeper understanding of the response characteristics of the larch-soil feedback loop in burned areas. How will larch change its nutrient utilization strategy in response to forest fire disturbance? Although some plant leaf traits are closely related to leaf litter chemical traits, the nutrient content of new leaves and leaf litter varies significantly due to nutrient reabsorption. How will the variability of nutrient reabsorption efficiency regulate the traits of larch leaf litter in burn sites? Are there differences in the decomposition rates of larch leaf litter in different burn sites? In the prior art, there are no reports on the decomposition rates of larch leaf litter regeneration in different types of burn sites and the analysis methods of key influencing factors. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention is based on biological (vegetation diversity, leaf litter characteristics) and non-biological environmental factors (soil physical and chemical properties, microclimate), to clarify the changing patterns of leaf litter decomposition rate of larch forests regenerated on different types of burned sites with fire intensity and recovery period, and to reveal the key influencing factors of leaf litter decomposition of larch forests regenerated on different types of burned sites, thereby providing theoretical support for accurately estimating the nutrient supply of larch forests on burned sites and optimizing nutrient cycle parameters.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A method for analyzing the decomposition rate and key influencing factors of larch leaf litter in different types of burned areas is provided, which specifically includes the following steps:

[0007] S1. Analysis of the regeneration of larch forest stands and environmental characteristics in different types of burned areas:

[0008] By investigating the structure of larch stands, shrub and grass diversity, microclimate, and soil physical and chemical properties in different types of burned areas, the dynamic characteristics of larch regeneration after forest fire disturbances of different intensities were revealed, and the relationship between larch characteristics and environmental factors was analyzed; by investigating the characteristics of new leaves, the nutrient acquisition strategies adopted by regenerating larch in different types of burned areas in response to environmental changes were revealed;

[0009] S2. Analysis of leaf litter characteristics of larch forest regeneration in different types of burned areas:

[0010] By collecting litter, the amount of larch litter returned in different burn sites was studied, revealing the changing patterns of litter biomass with fire intensity, forest characteristics, recovery period, soil physical and chemical properties, and microclimate factors; by analyzing the differences in the characteristics of litter in various plots, the quality characteristics of larch litter regeneration in various types of burn sites were revealed, and the driving mechanism of its changes was explained in combination with soil physical and chemical properties; by combining the characteristics of new leaves, the characteristics of nutrient reabsorption efficiency of larch regeneration in different types of burn sites were revealed;

[0011] S3. Analysis of leaf litter decomposition characteristics and main influencing factors of regeneration of larch forests in different types of burned areas:

[0012] On the basis of steps S1 and S2, by setting up litter decomposition bags, the decomposition characteristics of larch litter in different types of burn sites were explored, the correlation between biological and abiotic environmental factors and litter decomposition rate in different burn sites was analyzed, and the relative contribution of each factor affecting the decomposition rate of larch forest litter in different types of burn sites was analyzed using the structural equation model to reveal the key factors affecting decomposition.

[0013] Furthermore, in step S1, the microclimate includes temperature, humidity and leaf area index in the forest.

[0014] Furthermore, in step S1, the physical properties of the soil include soil density, maximum soil water holding capacity, minimum soil water holding capacity, and capillary water holding capacity; the chemical properties of the soil include pH value, organic carbon content, total nitrogen content, total phosphorus content, total potassium content, effective nitrogen content, effective phosphorus content, available potassium content, sucrase activity, urease activity, phosphatase activity, and catalase activity.

[0015] Furthermore, in step S1, the new leaf traits include pH value, leaf carbon content, leaf nitrogen content, leaf phosphorus content, leaf potassium content, lignin content, cellulose content, tannin content, specific leaf area, and leaf dry matter content.

[0016] Furthermore, in step S1, the indicators for measuring the diversity of vegetation composition are Margalef richness index D, Shannon index H′, Simpson index H and Pielou evenness index J, which are calculated as follows:

[0017]

[0018] Where N i is the importance value of the i-th species, N is the sum of the importance values ​​of all species, and S is the number of species in each plot;

[0019]

[0020] t 0.5 =-In(0.5) / k

[0021] t 0.95 =-ln(0.05) / k

[0022] In the formula, R i (%) is the N, P, K absorption efficiency of nutrient i, in percentage, C0 is the nutrient content of mature leaves, C t is the nutrient content of litter at time t; the decomposition rate is calculated using the negative exponential decay model proposed by Olson, where M0 is the initial dry mass of litter, M t is the residual dry mass of litter decomposed at time t, k is the annual decay constant, t 0.5 The time for 50% loss of mass, t 0.95 95% of the time for quality loss.

[0023] Furthermore, in step S3, the data were sorted using Excel 2016, and data analysis and drawing were performed using R language; the data were tested for homogeneity of variance using the bartlett.test() package of R language, and single-factor and two-factor ANOVAs were performed using the aov() package, with statistical significance set at p<0.05, and multiple comparisons were performed using the LSD.test() package; the differences in shrub and grass diversity, microclimate, soil physical and chemical properties, leaf traits, and litter traits of larch forests with different forest fire intensities and recovery times were analyzed; the species richness and Shannon index were calculated using the R language "vegan" package; NMDS and MRPP were used to analyze the understory under different fire intensities and different recovery times. Differences in vegetation composition; Pearson correlation analysis and PCA analysis were used to study the relationship between shrub and grass diversity, forest microclimate, soil nutrients, and leaf traits; the lmer() package was called in R language to construct a mixed effect model to analyze the influence of different environmental factors on leaf trait changes; the piecewiseSEM package was called in R language, and the lm() function was used to build a litter decomposition regression model, and the summary() function was called to view the model results, and the indicators with high collinearity between variables were deleted to ensure that the p value was greater than 0.05; the structural equation model was constructed using the screened indicators to analyze the key factors affecting the decomposition of larch litter.

[0024] The beneficial effects of the present invention are:

[0025] The present invention takes larch forests of different types of burned areas in Daxinganling region of my country as the research objects, investigates and analyzes the biotic and abiotic factors of various sites, clarifies the dynamic characteristics of larch community construction under different fire intensities and recovery times, and reveals the response strategies adopted by larch to adapt to environmental changes in leaf traits; identifies the main difference indicators of larch leaf litter traits in different types of burned areas, and reveals the direct or indirect influence mechanism of various factors on the decomposition of larch leaf litter, which is of great significance for accurately estimating the nutrient supply of larch forests in burned areas, and has an important scientific basis for optimizing nutrient cycle parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0027] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0028] Example

[0029] This example is based on the National Field Scientific Observation and Research Station of the Forest Ecosystem of Daxinganling, Inner Mongolia. It selects larch forests of different types (burn intensity and recovery period) regenerated in burned areas as the object. Through the analysis of forest stand characteristics, soil properties, microclimate, leaf traits, etc., it reveals the characteristics and decomposition characteristics of leaf litter in different types of sample plots, and deeply explores the key factors affecting the decomposition of leaf litter in larch forests in burned areas. It mainly includes the following three steps:

[0030] (1) Analysis of the regeneration and environmental characteristics of larch forests in different types of burned areas

[0031] By investigating the structure of larch stands, shrub and grass diversity, microclimate, and soil physical and chemical properties in different types of burned areas, the dynamic characteristics of larch regeneration after different intensities of forest fire disturbance were revealed, and the relationship between larch characteristics (including average breast diameter and average tree height) and environmental factors was analyzed. By investigating the characteristics of new leaves, the nutrient acquisition strategies adopted by regenerating larch in different types of burned areas in response to environmental changes were revealed.

[0032] (2) Analysis of leaf litter characteristics of larch forests regenerated in different types of burned areas

[0033] By collecting litter, the amount of larch litter returned in different burn sites was studied, revealing the changing patterns of litter biomass with factors such as fire intensity, forest characteristics, recovery period, soil physical and chemical properties, and microclimate. By analyzing the differences in the characteristics of litter in various plots, the quality characteristics of larch litter regeneration in various types of burn sites were revealed, and the driving mechanism of its changes was explained in combination with soil physical and chemical properties. By combining the characteristics of new leaves, the characteristics of nutrient reabsorption efficiency of larch regeneration in different types of burn sites were revealed.

[0034] (3) Analysis of leaf litter decomposition characteristics and main influencing factors of larch forest regeneration in different types of fire sites

[0035] On the basis of steps (1) and (2), leaf litter decomposition bags were set up to explore the decomposition characteristics of larch leaf litter in different types of burn sites, analyze the correlation between biological (vegetation diversity, leaf litter characteristics) and abiotic environmental factors (soil physical and chemical properties, microclimate) and leaf litter decomposition rate in different burn sites, and use structural equations to analyze the relative contribution of various factors affecting the decomposition rate of leaf litter in larch forests regenerated in different types of burn sites, revealing the key factors affecting decomposition.

[0036] Specifically, the method of this embodiment includes the following contents:

[0037] 1. Study area and sample plots

[0038] This example was carried out in Hulunbuir City, the northern section of Greater Khingan Range, my country (50°30′-52°30′N, 120°30′-122°30′E). Hulunbuir City is located in the northern part of Inner Mongolia Autonomous Region and has a cold temperate humid monsoon climate. It is dry in spring and prone to forest fires caused by lightning strikes. The forest type in the study area is a cold temperate coniferous forest with Larix gmelinii as the dominant tree species. The associated tree species include Betula platyphylla, Pinus sylvestris, Populus davidiana and other trees, as well as Rhododendron dauricum, Rhododendron tomentosum and other shrubs. It is typical and representative, and has obvious location advantages. The vegetation growth cycle in this area is about 155 days. It starts to sprout in late April, leaves unfold in May, open leaves from June to mid-August, change leaves in late August, fall leaves in September, and enter a dormant period in early October.

[0039] This example selects the lightly, moderately and severely burned larch forests after natural regeneration and recovery 13, 20 and 36 years after the fire as the study area, and sets up control plots in nearby unburned areas, including several lightly, moderately and severely burned plots in 13 years, several lightly, moderately and severely burned plots in 20 years, and several lightly, moderately and severely burned plots in 36 years. This example refers to the forest fire intensity classification proposed by Meng Meng (2020) in combination with the characteristics of surface combustibles and soil layer, herbaceous low shrub layer, tree layer and canopy layer, as shown in Table 1. The slope of the plots is controlled between 5 and 20 degrees, and the altitude range is 800-950m to ensure that the site conditions are basically similar. Each plot is 20×20m, and 5 replicates are set for each treatment, with a total of 60 plots.

[0040] Table 1 Survey contents and evaluation criteria of comprehensive fire index in Daxinganling forest area

[0041]

[0042] 2. Tree Survey

[0043] All trees with a breast diameter > 4 cm in the sample plot were investigated, including tree species, breast diameter, tree height, number, etc. The core of the tree was drilled using the growth cone method to determine the tree age.

[0044] 3. Survey of understory vegetation diversity

[0045] Three 5×5m and three 1×1m plots were set up in each plot using PVC pipes to investigate the species, abundance, and coverage of understory shrubs and herbs in July. The species and growth forms of all plants in the plots were identified using the Chinese Plant Species Information System (http: / / www.iplant.cn).

[0046] 4. Microclimate in the forest

[0047] The microclimate in the forest investigated in this embodiment includes the temperature (Temperature), humidity (Humidity) and leaf area index (Leafarea index) in the forest. The temperature and humidity in the forest were monitored for a long time using the MX2301A temperature-relative humidity recorder; images were taken from under the canopy using a 180-degree fisheye lens and a D70 digital camera (Nikon, Japan), and 10 photos were taken along the median line in each plot, and the images were loaded into the canopy analysis software (HemiView2.1 SR4, Delta-T, UK) for leaf area index analysis. At the same time, the coordinates and altitude of each plot were recorded using GPS (Trimble GIS, USA).

[0048] 5. Soil physical and chemical properties

[0049] The soil physical properties investigated in this embodiment include soil density, maximum soil moisture capacity, minimum soil moisture capacity, and capillary moisture capacity; the soil chemical properties include pH value, organic carbon content, total nitrogen content, total phosphorus content, total potassium content, available nitrogen content, available phosphorus content, available potassium content, invertase activity, urease activity, phosphatase activity, and catalase activity.

[0050] In July, soil profiles were dug from the test plots, and soil was taken in layers (0-10cm, 10-20cm, 20-40cm) with a ring cutter. Each layer was sampled 3 times to test soil physical properties. Soil was taken in layers along the median line in each test plot with a soil drill. Ten soil cores were taken from each plot. The soils of the same layers were mixed into a sample, spread on clean paper, and placed in a cool and ventilated place indoors to air dry. Stones and undecomposed organic matter were picked out, ground, and passed through a 2mm sieve. 1kg of soil samples were selected from the mixed soil using the quartering method. After fully mixing, a portion of the samples were taken and placed in a sealed bag, and the sampling information was noted. The remaining samples that had passed the 2mm sieve were further ground so that they all passed the 0.149mm sieve, placed in a sealed bag, and the sampling information was noted. The chemical and physical properties of the soil will refer to the soil-related treatment and analysis in the "Forestry Industry Standards of the People's Republic of China".

[0051] 6. Collection of fresh leaves and character determination

[0052] After the leaves are fully expanded (June-July), the fresh leaf traits are investigated. The leaf traits investigated in this embodiment include pH value, leaf carbon content, leaf nitrogen content, leaf phosphorus content, leaf potassium content, lignin content, cellulose content, tannin content, specific leaf area, and leaf dry matter content.

[0053] Sufficient leaves were collected from each larch plant at different heights and directions. Thirty leaves were randomly selected according to height and direction and immersed in water and stored in the dark for 12 h. The surface water was wiped off with absorbent paper and weighed with an electronic scale (0.0001 g) (fresh weight). The leaf features were scanned with a ScanMaker i800 scanner and stored in the form of a JPEG file (300 dpi). Leaf area (Leafarea) data were processed and analyzed using leaf area analysis software (WSeen's leafarea analysis System, model_LA-S, China). After analysis, the leaves were oven-dried at 65°C to constant weight and then weighed. Specific leaf area is expressed as the ratio of leaf area to dry mass; leaf dry matter content is expressed as the ratio of dry mass to fresh mass.

[0054] The remaining leaves collected from the same plot were mixed for chemical property analysis. The pH value of the leaves was determined by potentiometric method (LY / T 1239-1999); the organic carbon content was determined by potassium dichromate oxidation-external heating method (LY / T1237-1999); the total nitrogen of the leaves was determined by Kjeldahl method; the total phosphorus was determined by molybdenum antimony anti-absorption photometry; the total potassium was determined by flame photometry (NY / T 2017-2011); the lignin and cellulose content in the leaves was determined by acid detergent fiber method; the tannin content was determined by Folin-Ciocaiteu method; the samples were placed in a beaker filled with distilled water and soaked for 24 hours to determine the maximum water holding capacity of the leaves.

[0055] 7. Collection of fallen leaves and determination of their properties

[0056] Three 1×1m litter collection frames were arranged in each plot according to the top, middle and bottom. The litter frame was 1m above the ground to ensure that the gauze was large enough, and litter leaves were collected every 3 months. The collected litter was classified according to the tree species and weighed separately. The characteristics of larch litter were investigated during the leaf-falling period (September). 30 larch litter leaves were randomly selected from each plot to investigate the specific leaf area and leaf dry matter content of the litter leaves. The remaining larch litter leaves were mixed and treated. The test method for the chemical properties of the litter leaves was the same as that for fresh leaves.

[0057] 8. Leaf litter decomposition

[0058] Decomposition bags were made with collected larch leaf litter. The leaf litter decomposition bags were made of 20×30cm, 1mm mesh nylon net. 10.00g of dry leaf litter was placed in each bag as the initial weight. In October, 12 leaf litter decomposition bags were randomly placed in each plot according to the top, middle and bottom, and a total of 720 decomposition bags were placed. When placing, the surface litter layer was pushed aside, and the bags were tightly attached to the soil surface and fixed with PVC pipes. Three decomposition bags were randomly collected from each plot every 3 months for 1 year. The recycled bags were washed with clean water to remove excess soil, dried at 65℃ to constant weight, and then weighed.

[0059] 9. Data Analysis

[0060] The most commonly used indicators for measuring vegetation composition diversity are the Margalef richness index (D), the Shannon index (H′), the Simpson index (H) and the Pielou evenness index (J), which are calculated as follows:

[0061]

[0062]

[0063] Where N iis the importance value of the ith species, N is the sum of the importance values ​​of all species, and S is the number of species in each plot.

[0064]

[0065] t O5 -=-In(0.5) / k

[0066] t 0.95 =-ln(0.05) / k

[0067] In the formula, R i (%) is the absorption efficiency of nutrients i (N, P, K), expressed in percentage, C0 is the nutrient content of mature leaves, C t is the nutrient content of litter at time t; the decomposition rate is calculated using the negative exponential decay model proposed by Olson, where M0 is the initial dry mass of litter, M t is the residual dry mass of litter decomposed at time t (in years), k is the annual decay constant, t 0.5 The time for 50% loss of mass, t 0.95 95% of the time for quality loss.

[0068] The data were sorted using Excel 2016, and data analysis and graphics were performed using R. The R language bartlett.test() package was used to test the homogeneity of variance, and the aov() package was used for one-way and two-way ANOVA. The statistical significance was set at p<0.05, and the LSD.test() package was used for multiple comparisons. The differences in shrub and grass diversity, microclimate, soil physical and chemical properties, leaf traits, and litter traits of larch forests with different forest fire intensities and recovery times were analyzed. The R language "vegan" package was used to calculate species richness and Shannon index. NMDS and MRPP were used to analyze the differences in understory vegetation composition with different fire intensities and different recovery times. Pearson correlation analysis and PCA analysis were used to study the relationship between shrub and grass diversity, forest microclimate, soil nutrients, and leaf traits. The lmer() package was called in the R language to construct a mixed effect model to analyze the influence of different environmental factors on the changes in leaf traits. The piecewiseSEM package was called in R language, and the lm() function was used to build a leaf litter decomposition regression model. The summary() function was called to view the model results, and the indicators with high collinearity between variables were deleted to ensure that the p value was greater than 0.05. The structural equation model was constructed using the screened indicators to analyze the key factors affecting the decomposition of larch leaf litter.

[0069] The Greater Khingan Range is vast and is an important ecological barrier in northern my country. The long history of forest fires and recovery time provide an excellent research background for this application. This embodiment takes larch forests in different types of burned areas in the Greater Khingan Range of my country as the research object, investigates and analyzes the biological and abiotic factors of various sites, clarifies the dynamic characteristics of larch community construction under different fire intensities and recovery times, and reveals the response strategies adopted by the renewal of larch leaf traits to adapt to environmental changes; identifies the main difference indicators of larch leaf litter traits in different types of burned areas, and reveals the direct or indirect influence mechanism of various factors on the decomposition of larch leaf litter, which is of great significance for accurately estimating the nutrient supply of larch forests in burned areas, and has an important scientific basis for optimizing nutrient cycle parameters.

[0070] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0071] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An analysis method for the decomposition rate and key influencing factors of larch leaf litter regeneration in different types of fire sites, characterized in that: The specific steps include: S1. Analysis of the regeneration of larch forest stands and environmental characteristics in different types of burned areas: By investigating the structure of larch stands, shrub and grass diversity, microclimate, and soil physical and chemical properties in different types of burned areas, the dynamic characteristics of larch regeneration after forest fire disturbances of different intensities were revealed, and the relationship between larch characteristics and environmental factors was analyzed; by investigating the characteristics of new leaves, the nutrient acquisition strategies adopted by regenerating larch in different types of burned areas in response to environmental changes were revealed; S2. Analysis of leaf litter characteristics of larch forest regeneration in different types of burned areas: By collecting litter, the amount of larch litter returned in different burn sites was studied, revealing the changing patterns of litter biomass with fire intensity, forest characteristics, recovery period, soil physical and chemical properties, and microclimate factors; by analyzing the differences in the characteristics of litter in various plots, the quality characteristics of larch litter regeneration in various types of burn sites were revealed, and the driving mechanism of its changes was explained in combination with soil physical and chemical properties; by combining the characteristics of new leaves, the characteristics of nutrient reabsorption efficiency of larch regeneration in different types of burn sites were revealed; S3. Analysis of leaf litter decomposition characteristics and main influencing factors of regeneration of larch forests in different types of burned areas: On the basis of steps S1 and S2, by setting up litter decomposition bags, the decomposition characteristics of larch litter in different types of burn sites were explored, the correlation between biological and abiotic environmental factors and litter decomposition rate in different burn sites was analyzed, and the relative contribution of each factor affecting the decomposition rate of larch forest litter in different types of burn sites was analyzed using the structural equation model to reveal the key factors affecting decomposition.

2. The method for analyzing the decomposition rate and key influencing factors of larch leaf litter in different types of fire-burned sites according to claim 1, characterized in that: In step S1, the microclimate includes the temperature, humidity and leaf area index in the forest.

3. The method for analyzing the decomposition rate and key influencing factors of larch leaf litter in different types of fire-burned sites according to claim 1, characterized in that: In step S1, the physical properties of the soil include soil density, maximum soil water holding capacity, minimum soil water holding capacity, and capillary water holding capacity; the chemical properties of the soil include pH value, organic carbon content, total nitrogen content, total phosphorus content, total potassium content, effective nitrogen content, effective phosphorus content, available potassium content, sucrase activity, urease activity, phosphatase activity, and catalase activity.

4. The method for analyzing the decomposition rate and key influencing factors of larch leaf litter in different types of fire-burned sites according to claim 1, characterized in that: In step S1, the new leaf traits include pH value, leaf carbon content, leaf nitrogen content, leaf phosphorus content, leaf potassium content, lignin content, cellulose content, tannin content, specific leaf area, and leaf dry matter content.

5. The method for analyzing the decomposition rate and key influencing factors of larch leaf litter in different types of fire-burned sites according to claim 1, characterized in that: In step S1, the indicators for measuring vegetation composition diversity are Margalef richness index D, Shannon index H′, Simpson index H and Pielou evenness index J, which are calculated as follows: Where N i is the number of individuals of the i-th species, N is the sum of the number of individuals of all species, and S is the number of species in each plot; t 0.5 =-ln(0.5) / k t 0.95 =-ln(0.05) / k In the formula, R i (%) is the N, P, K absorption efficiency of nutrient i, in percentage, C0 is the nutrient content of mature leaves, C t is the nutrient content of litter at time t; the decomposition rate is calculated using the negative exponential decay model proposed by Olson, where M0 is the initial dry mass of litter, M t is the residual dry mass of litter decomposed at time t, k is the annual decay constant, t 0.5 The time for 50% loss of mass, t 0.95 95% of the time for quality loss.

6. The method for analyzing the decomposition rate and key influencing factors of larch leaf litter in different types of fire-burned sites according to claim 1, characterized in that: In step S3, the data were sorted using Excel 2016, and data analysis and drawing were performed using R language. The R language bartlett.test() package was used to test the homogeneity of variance of the data, and the aov() package was used to perform one-way and two-way ANOVA, with statistical significance set at p<0.

05. The LSD.test() package was used for multiple comparisons. The differences in shrub and grass diversity, microclimate, soil physical and chemical properties, leaf traits, and litter traits of larch forests with different forest fire intensities and recovery times were analyzed. The R language "vegan" package was used to calculate species richness and Shannon index. NMDS and MRPP were used to analyze the understory of forests with different fire intensities and different recovery times. Differences in vegetation composition; Pearson correlation analysis and PCA analysis were used to study the relationship between shrub and grass diversity, forest microclimate, soil nutrients, and leaf traits; the lmer() package was called in R language to construct a mixed effect model to analyze the influence of different environmental factors on leaf trait changes; the piecewiseSEM package was called in R language, and the lm() function was used to build a litter decomposition regression model, and the summary() function was called to view the model results, and the indicators with high collinearity between variables were deleted to ensure that the p value was greater than 0.05; the structural equation model was constructed using the screened indicators to analyze the key factors affecting the decomposition of larch litter.

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