Method for analyzing mechanism of action of frozen soil active layer on decomposition of litter leaves of larix dahurian

Abstract

The invention discloses a method for analyzing an action mechanism of a frozen soil active layer on decomposition of falling leaves of dahurian larch. The method specifically comprises the following steps: S1, analyzing the influence of the frozen soil active layer on forest stand and soil characteristics of the dahurian larch; s2, analyzing the response of the leaf characters of the dahurian larch and the phyllospheric microflora characteristics of the dahurian larch to a frozen soil active layer; s3, analyzing an action mechanism of a frozen soil active layer on decomposition of fallen leaves of the dahurian larch forest; according to the method, forest stand characteristics, soil physicochemical properties, leaf traits, phyllospheric microorganism characteristics, litter leaf traits and decomposition rates of the dahurian larch under frozen soil active layers with different thicknesses are investigated. The invention aims to analyze the structural characteristics of microflora at the phyllosphere of the dahurian larch under frozen soil active layers with different thicknesses, reveal a response strategy adopted by the leaf characters of the dahurian larch to adapt to environmental changes, explore the decomposition difference and main influence factors of the litter leaves, and clarify the action mechanism of the frozen soil active layers on the decomposition of the litter leaves.

Description

Technical Field

[0001] The invention relates to the technical field of forest cultivation, and in particular to a method for analyzing the mechanism of action of a permafrost active layer on the decomposition of leaf litter of Larix gmelinii. Background Art

[0002] The Greater Khingan Range is an important ecological protection barrier in northern my country. Larix gmelina is the climax community and endemic tree species in the final stage of the succession process of the natural forest ecosystem in the Greater Khingan Range forest area. The quality and decomposition rate of its leaf litter directly affect the carbon balance and nutrient cycle of the ecosystem, and are crucial to the maintenance of forest productivity. The Greater Khingan Range forest area is the only cold temperate forest ecosystem in my country and the main distribution area of ​​high-latitude permafrost in my country. Due to its relatively low latitude, the permafrost in the Greater Khingan Range is warm and thin. The permafrost shows a regional degradation trend. Against the background of global warming, the study of the hydrothermal changes of permafrost in the Greater Khingan Range forest area and its impact on the Larix gmelina ecosystem has become a hot topic of concern for Chinese foresters and ecologists. At present, Chinese scholars have found that the frozen soil environment will inhibit the growth and development of Larix gmelina. Soil physical and chemical properties, leaf litter characteristics, and microbial composition are all important factors affecting leaf litter decomposition. However, in the existing technology, there are relatively few studies on the impact of changes in the thickness of the active layer of permafrost in the Greater Khingan Range on the decomposition process of leaf litter in Larix gmelinii, especially a lack of research on the mechanism of action. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to carry out research on the decomposition characteristics and mechanism of leaf litter of Larix gmelinii under different thicknesses of frozen soil active layers. By analyzing the leaf traits and leaf-sphere microbial community structure characteristics of Larix gmelinii under different thicknesses of frozen soil active layers, combined with the decomposition characteristics of Larix gmelinii under different thicknesses of frozen soil active layers, the mechanism of action of the frozen soil active layer on leaf litter decomposition is elucidated. The research results will provide an important theoretical basis for accurately predicting the carbon dynamics and nutrient cycle process of Larix gmelinii in the Greater Khingan Range forest area.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0005] A method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii is provided, which specifically comprises the following steps:

[0006] S1. Analysis of the impact of the permafrost active layer on the Dahurian larch forest and soil characteristics:

[0007] The changing patterns of soil physical and chemical properties of the permafrost active layer at different periods and depths were analyzed; the forest structure, community diversity, and local microclimate of the Dahurian larch forest under the permafrost active layer of different thicknesses were investigated to clarify the changing patterns of the influence of the permafrost active layer on the characteristics of the Dahurian larch forest, and to reveal the correlation between the characteristics of the larch forest and the internal environmental factors of the community;

[0008] S2. Analysis of the response of leaf traits and phyllosphere microbial community characteristics of Larix gmelinii to the permafrost active layer:

[0009] Fresh leaves of Larix gmelinii from permafrost layers of different thicknesses were collected, and the leaf traits and phyllosphere microbial community characteristics of Larix gmelinii were analyzed to clarify the adaptation of Larix gmelinii leaf traits to the permafrost active layer; the relative contribution of each factor to the composition and diversity of the phyllosphere microbial community was quantified by principal coordinate analysis and variance decomposition methods;

[0010] S3. Analysis of the mechanism of the effect of the active layer of permafrost on the decomposition of leaf litter in the Larix gmelinii forest:

[0011] Combined with the leaf litter data, the influence of the phyllospheric microbial legacy effect on the structure of the leaf litter microbial community was explored, and the characteristics of the leaf litter of Larix gmelinii under different thicknesses of permafrost active layers were revealed; by setting up leaf litter decomposition bags, the differences in the decomposition rates of Larix gmelinii leaf litter under different thicknesses of permafrost active layers were analyzed, the key factors affecting the decomposition of Larix gmelinii leaf litter were found, and the mechanism of action of the permafrost active layer on the decomposition of Larix gmelinii leaf litter was revealed.

[0012] Furthermore, in step S1, the Margalef richness index D, the Shannon index H′, the Simpson index H and the Pielou evenness index J are used to measure the diversity of community composition.

[0013] Furthermore, the community composition diversity is measured according to the following formula:

[0014]

[0015] Where N i is 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.

[0016] Furthermore, in step S1, the microclimate in the forest includes the temperature and humidity in the forest.

[0017] 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 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.

[0018] Furthermore, in step S2, the 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.

[0019] Furthermore, in step S3, the microbial diversity and composition of leaf litter are determined by microbial high-throughput sequencing; and the nutrient reabsorption efficiency of Larix gmelinii leaves is calculated using the following formula:

[0020]

[0021] t 0.5 =-ln(0.5) / k

[0022] t 0.95 =-ln(0.05) / k

[0023] 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.

[0024] Furthermore, in step S3, R language was used for data analysis and drawing; bartlett.test was used to test the homogeneity of variance of the data, and aov was used for one-way analysis of variance, with statistical significance set at p<0.05; LSD.test was used to compare the differences in community diversity, soil physical and chemical properties, leaf traits, and leaf litter traits of Larix gmelinii forests with different thicknesses of frozen soil active layers; vegan was used to calculate the richness of understory vegetation and the Shannon index, and NMDS and MRPP were used to analyze the differences; Pearson correlation analysis and PCA analysis were used to study the relationship between community diversity, soil nutrients and leaf traits; based on the OTU classification level sample table, a Venn diagram was made to show the composition and overlap of bacterial and fungal OTUs in Larix gmelinii leaf litter and its decomposition process under different thicknesses of frozen soil active layers; Mothur was used to calculate the Shannon index, Sobs index, and Chao1 index to reflect the diversity of the community; based on the classification information and abundance data of fungal and bacterial communities, One-way ANOVA tests the abundance differences of species in different groups; Ternary package is used to draw a ternary phase diagram to show the distribution ratio of dominant fungi and bacteria in the litter of Larix gmelinii in different thicknesses of frozen soil active layers;

[0025] Mantel tests were used to analyze and test the correlation between the leaf litter nutrient matrix and the fungal and bacterial community matrix at the phylum and genus levels; the Pearson correlation coefficient and difference significance between leaf nutrient indicators and fungal and bacterial species were calculated to evaluate the relationship between different communities, species and leaf litter nutrient variables. The Fungal traits functional trait database was used to functionally annotate the microbial communities in the samples, and a bar graph was drawn to show the main microbial ecological types in the leaf litter of Larix gmelinii in different thicknesses of frozen soil active layers;

[0026] The lmer mixed effects model was constructed to analyze the influence of different environmental factors on leaf traits and phyllospheric microbial changes. The lm() function was used to construct a regression model for leaf litter decomposition, 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 Larix gmelinii leaf litter and to clarify the mechanism of action of the permafrost active layer on leaf litter decomposition.

[0027] The beneficial effects of the present invention are:

[0028] Based on the scientific hypothesis that "the thickness of the permafrost active layer affects the physical and chemical properties of the soil, thereby changing the leaf nutrient acquisition strategy and phyllosphere microbial characteristics, indirectly changing the quality of leaf litter, and thus affecting the decomposition process of leaf litter", the present invention takes the Dahurian larch forest under the permafrost active layer of different thicknesses as the research object, and investigates the forest characteristics, soil physical and chemical properties, Dahurian larch leaf traits, phyllosphere microbial characteristics, leaf litter quality and the decomposition rate of its leaf litter. In order to analyze the characteristics of the leaf sphere microbial community structure of Dahurian larch under the permafrost active layer of different thicknesses, reveal the response strategies adopted by the leaf traits of Dahurian larch to adapt to environmental changes, explore the differences in leaf litter decomposition and the main influencing factors, and clarify the mechanism of action of the permafrost active layer on leaf litter decomposition, so as to provide an important theoretical basis for accurately predicting the carbon dynamics and nutrient cycle process of Dahurian larch in the Greater Khingan Range forest area. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0030] 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.

[0031] Example

[0032] This embodiment is based on the National Field Scientific Observation and Research Station of Daxinganling Forest Ecosystem in Inner Mongolia, and takes Daxinganling larch forests under different thicknesses of frozen soil active layers as the research object, and mainly includes the following three steps:

[0033] 1. Study on the influence of permafrost active layer on Larix gmelinii forest stands and soil characteristics

[0034] The variation patterns of soil physical and chemical properties of the permafrost active layer at different periods (thaw (April-May), freezing (September-October), growing season (June-August)) and different depths (0-10cm, 10-20cm, 20-40cm) were analyzed. By investigating the stand structure, community diversity, and local microclimate of the Dahurian larch forest under the permafrost active layer of different thicknesses, the variation patterns of the influence of the permafrost active layer on the characteristics of the Dahurian larch forest were clarified, and the correlation between the characteristics of the larch forest and the internal environmental factors of the community was revealed.

[0035] 2. Response of leaf traits and phyllosphere microbial community characteristics of Larix gmelinii to the permafrost active layer

[0036] Fresh leaves of Larix gmelinii were collected from permafrost layers of different thicknesses, and the leaf traits and phyllosphere microbial community characteristics of Larix gmelinii were analyzed to clarify the adaptation of Larix gmelinii leaf traits to the permafrost active layer. The relative contribution of each factor to the composition and diversity of the phyllosphere microbial community was quantified by principal coordinate analysis and variance decomposition.

[0037] 3. Study on the mechanism of action of permafrost active layer on leaf litter decomposition in Larix gmelinii forest

[0038] Combined with leaf litter data, the influence of the legacy effect of phyllospheric microorganisms on the structure of leaf litter microbial communities was explored, and the characteristics of leaf litter of Larix gmelinii under different thicknesses of permafrost active layers were revealed. By setting up leaf litter decomposition bags, the differences in the decomposition rates of Larix gmelinii under different thicknesses of permafrost active layers were analyzed, the key factors affecting the decomposition of Larix gmelinii leaf litter were found, and the mechanism of action of the permafrost active layer on the decomposition of Larix gmelinii leaf litter was revealed.

[0039] Specifically, this embodiment includes the following contents:

[0040] 1. Sample site conditions

[0041] This example was carried out at a permafrost observation plot at the National Field Scientific Observation and Research Station for the Greater Khingan Range Forest Ecosystem in Inner Mongolia.

[0042] The method of selecting the thickness of the frozen soil active layer by using the frozen soil detection hole was used. The frozen soil active layer thickness was 0.5m, 1m, and 2m, respectively. A 20m×20m sample plot with basically the same site conditions such as slope, slope aspect, and altitude was set at each frozen soil active layer thickness. In order to conduct a comparative experiment on the impact of frozen soil on vegetation, three pieces of frozen soil in non-frozen areas were selected as control CK (20m×20m). In this embodiment, a total of 12 sample plots were set.

[0043] Table 1. Overview of frozen soil well sample sites

[0044]

[0045] 2. Forest stand characteristics survey

[0046] (1) Survey of trees, shrubs and grasses

[0047] All trees with a breast diameter greater than 4 cm in the plot were investigated, including species, breast diameter, height of tree, number, etc. The core of the tree was drilled using the growth cone method to determine the tree age. Three 5×5m shrub survey plots and three 1×1m herb survey plots were randomly set up in each plot according to the upper, middle and lower slopes. The species, abundance and coverage of understory shrubs and herbs were investigated in July. The species and growth forms of all plants in the plots were identified through the Chinese Plant Species Information System (http: / / www.iplant.cn). The Margalef richness index (D), Shannon index (), Simpson index (H) and Pielou evenness index (J) were used to measure the diversity of community composition.

[0048]

[0049] Where N i is 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.

[0050] (2) Microclimate in the forest

[0051] The microclimate in the forest investigated in this embodiment includes the temperature and humidity in the forest. The temperature and humidity in the forest are monitored for a long time using the MX2301A temperature-relative humidity recorder.

[0052] (3) Soil physical and chemical properties and microorganisms

[0053] The soil physical properties investigated in this embodiment include soil density, maximum soil moisture capacity, minimum soil moisture capacity, and capillary moisture capacity; the 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.

[0054] In July, soil was collected from the test plots in layers (0-10cm, 10-20cm, 20-40cm) using a circular cutter. Each layer was sampled three times to test soil physical properties. Soil was collected from each test plot along the median line using a soil drill. Ten soil cores were taken from each plot, and stones and undecomposed organic matter were picked out. The soil from the same layer was mixed into a mixed sample and spread on a clean paper. Then a small amount of fresh soil sample from the surface layer was taken into a 25mL centrifuge tube, stored in a dry ice box, and quickly brought back to the laboratory and stored in a -80℃ ultra-low temperature refrigerator for soil microbial DNA extraction. The rest of the soil was placed in a cool and ventilated place indoors to air dry, ground, and passed through a 2mm sieve. A 1kg soil sample was selected from the mixed soil using the quartering method. After fully mixing, a portion of the sample was taken and placed in a sealed bag, and the sampling information was noted. The remaining sample that had passed the 2mm sieve was further ground so that it 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. The diversity and composition of soil microorganisms will be determined using microbial high-throughput sequencing.

[0055] 3. Leaf traits and microbial community determination

[0056] (1) Leaf collection

[0057] Ten standard Dahurian larch trees were selected for each plot. Samples were collected from the four directions of southeast, northwest, and northeast after full leaf expansion (June-July) and before leaf fall (September). 30 to 35 healthy and mature leaves were collected from each direction. The leaves collected from each tree were mixed into a mixed sample. Masks and disposable sterile gloves were worn during the entire sampling process. Disposable gloves were replaced between different plots, and scissors and pruning shears were disinfected with alcohol spray bottles and sterile cotton balls to avoid mixing samples. The collected samples were stored in ice boxes, transported back to the laboratory, and the initial sample processing was completed within 24 hours. The collected leaves were divided into two parts, one for trait determination and the other for initial sample processing in preparation for DNA extraction.

[0058] (2) Leaf trait investigation

[0059] 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. The collected leaves were soaked in water and stored in the dark for 12 hours. The surface water was wiped with absorbent paper and weighed (fresh weight) with an electronic scale (0.0001g). The leaf features were scanned with a ScanMaker i800 scanner and stored in the form of a JPEG file (300dpi). The leaf area data was processed and analyzed using leaf area analysis software (WSeen's leaf area analysis System, model_LA-S, China). After analysis, the leaves were oven-dried at 65°C to constant weight and then weighed. The specific leaf area was expressed as the ratio of leaf area to dry mass; the leaf dry matter content was expressed as the ratio of dry mass to fresh mass. 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.

[0060] (3) Leaf microbial assay

[0061] Immerse 10 to 15 plant leaves in sterile PBS solution at 180 rpm for 20 min; remove the leaves and repeat the above steps; remove the leaves and wash them in an ultrasonic cleaner for 10 min (parameters: 160 W, 30 s / 30 s); collect the three washes, filter through a 0.22 μm filter, collect the filter and store it in an ultra-low temperature refrigerator (-80 ° C). The diversity and composition of leaf microorganisms were determined by microbial high-throughput sequencing.

[0062] 4. Collection of fallen leaves and determination of their properties

[0063] Three 1×1m leaf litter collection frames were arranged in each plot according to the top, middle and bottom. The leaf litter frame was 1m above the ground to ensure that the gauze was large enough, and leaf litter was collected every 3 months. The leaf litter characteristics of larch were investigated during the leaf fall period (September). 30 larch leaf litters were randomly selected from each plot to investigate the leaf area and leaf dry matter content of the leaf litters. The remaining larch leaf litters were mixed and treated. The chemical properties of the leaf litters were tested in the same way as for fresh leaves. The microbial diversity and composition of the leaf litters were determined by microbial high-throughput sequencing. The nutrient reabsorption efficiency of Larix gmelinii leaves was calculated using the following formula:

[0064]

[0065] t 0.5 =-ln(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] 5. Leaf litter decomposition

[0069] Decomposition bags were made from leaf litter collected from Larix gmelinii during the leaf fall period. The leaf litter decomposition bags were made of nylon nets with a size of 20cm×30cm and a mesh size of 1mm. 10.0g of dry leaf litter was placed in each bag as the initial weight. In October, 36 leaf litter decomposition bags were randomly placed in the upper, middle and lower parts of each plot. 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 month for 1 year. The recycled bags were washed with clean water to remove excess soil, dried at 65°C to constant weight, and then weighed.

[0070] 6. Data Analysis

[0071] Data analysis and drawing were performed using R language. Bartlett.test was used to test the homogeneity of variance of the data, and aov was used for one-way analysis of variance. The statistical significance was set at p<0.05. LSD.test was used to compare the differences in community diversity, soil physical and chemical properties, leaf traits, and litter traits of Larix gmelinii forests with different thicknesses of frozen soil active layers. Vegan was used to calculate the richness of understory vegetation and the Shannon index, and NMDS and MRPP were used to analyze the differences. Pearson correlation analysis and PCA analysis were used to study the relationship between community diversity, soil nutrients and leaf traits. Based on the OTU classification level sample table, a Venn diagram was made to show the composition and overlap of bacterial and fungal OTUs in the litter of Larix gmelinii under different thicknesses of frozen soil active layers and their decomposition process; Mothur was used to calculate the Shannon index, Sobs index, and Chao1 index to reflect the diversity of the community. Based on the classification information and abundance data of fungal and bacterial communities, One-way ANOVA was used to test the abundance differences of each species in different groups. The Ternary package was used to draw a ternary phase diagram to show the distribution ratios of dominant fungi and bacteria in the litter of Larix gmelinii in permafrost active layers of different thicknesses.

[0072] Mantel tests were used to analyze and test the correlation between the leaf litter nutrient matrix and the fungal and bacterial community matrix at the phylum and genus levels; the Pearson correlation coefficient and difference significance between leaf nutrient indicators and fungal and bacterial species were calculated to evaluate the relationship between different communities, species and leaf litter nutrient variables. The Fungal traits database was used to functionally annotate the microbial communities in the samples, and a bar graph was drawn to show the main microbial ecological types in the leaf litter of Larix gmelinii in different thicknesses of frozen soil active layers.

[0073] The lmer mixed effect model was used to analyze the influence of different environmental factors on leaf traits and phyllospheric microorganisms. The lm() function was used to build a regression model for leaf litter decomposition, 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 selected indicators to analyze the key factors affecting the decomposition of Larix gmelinii leaf litter.

[0074] The present invention investigates the characteristics of Larix gmelinii forest stands, soil physical and chemical properties, Larix gmelinii leaf traits, phyllosphere microbial characteristics, leaf litter traits and their decomposition rates under different thicknesses of frozen soil active layers. The aim is to analyze the characteristics of the leaf-sphere microbial community structure of Larix gmelinii under different thicknesses of frozen soil active layers, reveal the response strategies adopted by Larix gmelinii leaf traits to adapt to environmental changes, explore the differences in leaf litter decomposition and the main influencing factors, and clarify the mechanism of action of the frozen soil active layer on leaf litter decomposition.

[0075] 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.

[0076] 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. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii is characterized by: The specific steps include: S1. Analysis of the impact of the permafrost active layer on the Dahurian larch forest and soil characteristics: The changing patterns of soil physical and chemical properties of the permafrost active layer at different periods and depths were analyzed; the forest structure, community diversity, and local microclimate of the Dahurian larch forest under the permafrost active layer of different thicknesses were investigated to clarify the changing patterns of the influence of the permafrost active layer on the characteristics of the Dahurian larch forest, and to reveal the correlation between the characteristics of the larch forest and the internal environmental factors of the community; S2. Analysis of the response of leaf traits and phyllosphere microbial community characteristics of Larix gmelinii to the permafrost active layer: Fresh leaves of Larix gmelinii from permafrost layers of different thicknesses were collected, and the leaf traits and phyllosphere microbial community characteristics of Larix gmelinii were analyzed to clarify the adaptation of Larix gmelinii leaf traits to the permafrost active layer; the relative contribution of each factor to the composition and diversity of the phyllosphere microbial community was quantified by principal coordinate analysis and variance decomposition methods; S3. Analysis of the mechanism of the effect of the active layer of permafrost on the decomposition of leaf litter in the Larix gmelinii forest: Combined with the leaf litter data, the influence of the phyllospheric microbial legacy effect on the structure of the leaf litter microbial community was explored, and the characteristics of the leaf litter of Larix gmelinii under different thicknesses of permafrost active layers were revealed; by setting up leaf litter decomposition bags, the differences in the decomposition rates of Larix gmelinii leaf litter under different thicknesses of permafrost active layers were analyzed, the key factors affecting the decomposition of Larix gmelinii leaf litter were found, and the mechanism of action of the permafrost active layer on the decomposition of Larix gmelinii leaf litter was revealed.

2. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii according to claim 1, characterized in that: In step S1, the Margalef richness index D, Shannon index H′, Simpson index H and Pielou evenness index J are used to measure the diversity of community composition.

3. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii according to claim 2, characterized in that: The community composition diversity is measured according to the following formula: Where N i is 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.

4. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii according to claim 1, characterized in that: In step S1, the microclimate in the forest includes the temperature and humidity in the forest.

5. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii 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 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.

6. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii according to claim 1, characterized in that: In step S2, 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.

7. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii according to claim 1, characterized in that: In step S3, the microbial diversity and composition of leaf litter are determined using microbial high-throughput sequencing; The nutrient reabsorption efficiency of Larix gmelinii leaves was calculated using the following formula: t 0.5 =-ln(0.5) / k t 0.95 =-ln(0.05) / k 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.

8. The method for analyzing the mechanism of action of the active layer of frozen soil on the decomposition of leaf litter of Larix gmelinii according to claim 1, characterized in that: In step S3, data analysis and drawing were performed using R language; bartlett.test was used to test the homogeneity of variance of the data, and aov was used for one-way analysis of variance, with statistical significance set at p<0.05; LSD.test was used to compare the differences in community diversity, soil physical and chemical properties, leaf traits, and litter traits of Larix gmelinii forests with different thicknesses of frozen soil active layers; vegan was used to calculate the richness of understory vegetation and Shannon index, and NMDS and MRPP were used to analyze the differences; Pearson correlation analysis and PCA analysis were used to study the relationship between community diversity, soil nutrients and leaf traits; Based on the OTU classification level sample table, a Venn diagram was made to show the composition and overlap of bacterial and fungal OTUs in the leaf litter of Larix gmelinii under different thicknesses of frozen soil active layers and during their decomposition; Mothur was used to calculate the Shannon index, Sobs index, and Chao1 index to reflect the diversity of the community; based on the classification information and abundance data of fungal and bacterial communities, One-way ANOVA was used to test the abundance differences of each species in different groups; the Ternary package was used to draw a ternary phase diagram to show the distribution ratios of dominant fungi and bacteria in the leaf litter of Larix gmelinii under different thicknesses of frozen soil active layers; Mantel tests were used to analyze and test the correlation between the leaf litter nutrient matrix and the fungal and bacterial community matrix at the phylum and genus levels; the Pearson correlation coefficient and difference significance between leaf nutrient indicators and fungal and bacterial species were calculated to evaluate the relationship between different communities, species and leaf litter nutrient variables. The Fungal traits functional trait database was used to functionally annotate the microbial communities in the samples, and a bar graph was drawn to show the main microbial ecological types in the leaf litter of Larix gmelinii in different thicknesses of frozen soil active layers; The lmer mixed effects model was constructed to analyze the influence of different environmental factors on leaf traits and phyllospheric microbial changes. The lm() function was used to construct a regression model for leaf litter decomposition, 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 Larix gmelinii leaf litter and to clarify the mechanism of action of the permafrost active layer on leaf litter decomposition.

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