Diffusion traceability method for extrinsic invasive plant by using stable isotope

Abstract

The invention discloses a diffusion traceability method for external invasive plants by using stable isotopes. The diffusion traceability method comprises the steps of external invasive plant traceability analysis and external invasive plant diffusion risk identification. Wherein the alien invasive plant traceability analysis comprises the steps of S1, plant sample collection, S2, sample pretreatment, S3, stable isotope determination, and S4, analysis of a diffusion source and a diffusion path of an alien invasive plant; the alien invasive plant diffusion risk identification comprises the steps of P1, constructing a diffusion network of alien invasive plants and P2, identifying a diffusion risk area. According to the method, by measuring the stable isotope ratio of the plants in the new introduction site and the potential source site and combining a multi-dimensional analysis method, the source and diffusion path of the alien invasive plants are traced, and the traceability precision is high; compared with a traditional gene analysis method, the method has the advantages that the cost is lower, the experiment efficiency is higher, and the traceability cost can be remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of biological traceability, and in particular to a diffusion traceability method for invasive alien plants using stable isotopes. Background Art

[0002] The invasion of alien species has become an important factor in the loss of global biodiversity and the degradation of ecosystem functions. Solanum syringae is a key alien invasive species under national management. It is a vicious invasive plant in the natural grasslands of the agricultural and pastoral transition zone in northern my country. It has caused great harm to the grassland and farmland ecosystems in Liaoning, Inner Mongolia and Hebei. It is still being introduced and spread, showing an exponential growth trend. The main problem currently faced is that the introduction route and source are unclear, which greatly restricts the efficiency of prevention and control. Therefore, accurately identifying the source of spread of alien invasive plants such as Solanum syringae, especially tracking their spread routes, is crucial for the prevention and control of alien invasive plants.

[0003] Due to the lack of traceability analysis methods for the spread of invasive alien plants such as Solanum serrata, the current prevention and control of Solanum serrata is extremely passive and the prevention and control efficiency is extremely low. Existing traceability methods mainly rely on the morphological characteristics and molecular genetic structure of plants. These methods have many limitations when dealing with plant invasions in a rapidly spreading and complex ecological background. On the one hand, when the invasive alien plant is introduced once, the gene pool of the species is very limited and the variability of genetic markers is insufficient, resulting in samples collected from multiple locations showing similar genetic characteristics, making it impossible to effectively distinguish samples from different sources; on the other hand, the genetic traceability method is costly and time-consuming, requiring a large number of sample collections and high-precision gene analysis, and complex data processing and interpretation, which increases costs and experimental complexity; in addition, the use of molecular genetic methods can only analyze the differences of the invasive alien plants themselves and obtain information on their sources of spread, but their spread pathways cannot be identified and judged. Summary of the invention

[0004] The purpose of the present invention is to provide a method for tracing the spread of alien invasive plants using stable isotopes, which can trace the source and spread path of alien invasive plants through the stable isotope ratio in the sample.

[0005] The present invention is implemented by the following technical solutions: A method for tracing the spread of invasive alien plants using stable isotopes, which includes tracing the spread of invasive alien plants and identifying the risk of invasive alien plants spreading; wherein: The tracing analysis of the alien invasive plants includes the following steps S1-S4; S1. Plant sample collection: S11. Determine the new place of introduction; S12. Collect invasive alien plants and crop products mixed with the invasive alien plants from the new place of introduction, which may be one or more, as plant samples from the new place of introduction; S13. Collect data to obtain the potential source of the plant samples from the new place of introduction; S14. Collect the invasive alien plants and crop products from the potential source as plant samples from the potential source; the invasive alien plants and crop products collected should be selected from plants without insect eyes and lesions for sampling, and the plant parts collected from the new place of introduction and the potential source should be the same; S2, sample pretreatment; S3. Stable isotope determination. Since the ratio of stable isotopes in organisms is closely related to the environment in which they live, and different geographical regions, ecosystems and climatic conditions will lead to differences in these isotope ratios, by analyzing the composition of stable isotopes in the invasive alien plants, their possible growth areas or diffusion paths can be inferred. The source and path of diffusion can also be further confirmed by detecting the stable isotopes of the diffusion medium (referring to the crop products) themselves. S4. Analyze the sources and pathways of spread of invasive alien plants; The risk identification of the spread of invasive alien plants includes the following steps P1 and P2; P1, constructing a diffusion network of the invasive alien plant; P11, identifying diffusion network nodes; P12, generating road network links between the diffusion network nodes; P13, constructing a trade network for the crop products based on the diffusion network nodes and the road network links; P2. Identify diffusion risk areas: Identify risk areas for invasion by the invasive alien plants in the trade network of the crop products by analyzing the correlation between the centrality of the diffusion network nodes and the distribution frequency of the invasive alien plants.

[0006] Furthermore, the method for determining the new introduction site in step S11 is: based on the national spatiotemporal distribution data of the alien invasive plants, the areas where the alien invasive plants have been newly recorded to have appeared in the past five years are selected as the new introduction sites.

[0007] Furthermore, the data collection in step S13 includes: investigating the sources of the agricultural products purchased in the newly introduced areas, collecting spatiotemporal data of the planting of the agricultural products in the country, and collecting spatiotemporal data of the occurrence of the alien invasive plants in the country.

[0008] Furthermore, the preprocessing of step S2 includes: S21. Dust and impurity removal: The collected plant parts must be stored at room temperature in a dry and ventilated place to avoid rotting, and then pollutants (such as dust and dirt) on the plant surface must be removed; S22, drying: drying the newly introduced plant samples and the potential source plant samples after dust and impurity removal to constant weight; S23, crushing: crushing the dried plant samples of the newly introduced area and the plant samples of the potential source area, and then sieving; S24. Sampling: Take 2-3 mg of the sieved sample as a subsample.

[0009] Furthermore, the step S3 specifically comprises performing stable isotope determination on the pretreated sub-sample to calculate the stable isotope ratio of the sub-sample; the stable isotope ratio includes δ 13 C (the carbon isotope ratio reflects the source and environmental characteristics of plant photosynthesis. Plants in different regions will show different carbon isotope values, which can distinguish different ecological regions), δ 15 N (nitrogen isotope ratios help identify the soil type and fertilization history of plant growth; since nitrogen isotopes vary in different soil and environmental conditions, they are important indicators of the source of spread of invasive alien plants), δ 18 O (oxygen isotope ratios can reflect changes in water sources; plants absorb water through different water sources under different climatic conditions, so oxygen isotope ratios can provide information about the water source of plant growth), δ 2 H (Water in plants is absorbed by the roots and enters the plant tissues through transpiration. The hydrogen isotope ratio of water is affected by the hydrogen isotope composition of the local water source (such as groundwater, precipitation, river water, etc.); water from different sources has different δ 2 H value, so with the help of hydrogen isotopes, the type of water source and the source of water for plants can be determined).

[0010] Furthermore, the step S4 is specifically as follows: using statistical methods (such as cluster analysis, principal component analysis, multivariate regression analysis, etc.) to process the stable isotope ratios of the sub-samples of the newly introduced plant samples and the stable isotope ratios of the sub-samples of the plant samples of the potential source, so as to analyze the diffusion sources and diffusion paths of the alien invasive plants.

[0011] Furthermore, the step P11 is specifically as follows: according to the diffusion source and diffusion path of the alien invasive plant analyzed in the step S4, the diffusion network nodes of the alien invasive plant are determined, including the production site of the crop product, the logistics transit center, the distribution site of the crop product, the grass market for transporting the crop product, and the market or farmers and herdsmen who receive the crop product.

[0012] Furthermore, in step P2, the measurement indicators of the centrality include degree centrality, betweenness centrality and proximity centrality; centrality reflects the importance of diffusion network nodes in the diffusion network, and also reflects the invasion risk of alien invasive plants. In the trade network of the crop products constructed in this scheme, the degree centrality of the diffusion network node reflects the number of nodes that trade crop products with the node. The high degree centrality means that the point has trade relations with more regions, which further indicates that the point plays a hub role in the trade network; proximity centrality reflects the number of times that the nodes need to be transferred during the trade; betweenness centrality reflects the number of times that the nodes need to pass through a certain node for transfer during the trade; Degree Centrality D(i) The calculation formula is shown in formula (1): (1); In the formula, d i is the degree of node i, N is the total number of nodes in the network; Betweenness Centrality C(i) The calculation formula is shown in formula (2): (2); In the formula, β ij Indicates the starting node i To the end j The number of links contained in the shortest path, N is the total number of nodes in the network; Closeness Centrality B(i) The calculation formula is shown in formula (3): (3) In the formula α xy For Node x To Node y The number of all shortest paths, α xy (i) For Node x To Node y And through the node i The number of all shortest paths.

[0013] Furthermore, when the degree centrality, the betweenness centrality, and the closeness centrality of the diffusion network node are all significantly correlated with the distribution frequency of the alien invasive plants, the diffusion network node is determined to be a high-risk invasion area; when one or two of the degree centrality, the betweenness centrality, and the closeness centrality of the diffusion network node are significantly correlated with the distribution frequency of the alien invasive plants, the diffusion network node is determined to be a medium-risk invasion area; when the degree centrality, the betweenness centrality, and the closeness centrality of the diffusion network node do not show a significant correlation with the distribution frequency of the alien invasive plants, the diffusion network node is determined to be a low-risk invasion area.

[0014] Advantages of the present invention: (1) High traceability accuracy: Stable isotope ratios are significantly affected by environmental and geographical factors and show spatial heterogeneity. By measuring the stable isotope ratios of plants from newly introduced areas and potential source areas, and combining geographic information systems (GIS) with multi-dimensional analysis methods such as spatial analysis and cluster analysis, it is possible to trace the sources and diffusion paths of alien invasive plants under changing environmental conditions, and to analyze the invasion risk of alien invasive plants at a certain node. The traceability accuracy is high, and the traceability results are more accurate and reliable.

[0015] (2) Low cost and high efficiency: Compared with traditional genetic analysis methods, the cost of stable isotope single sample testing is low, and only 1-3 samples need to be collected at each location for testing. In addition, stable isotope detection and analysis takes a short time, with the detection time for a single sample being 10-15 minutes. Therefore, it has lower cost and higher experimental efficiency, which can significantly reduce the cost of traceability.

[0016] (3) Convenient and easy to store: The samples used to determine isotopes are not limited to a specific part of the plant. It is only required that the samples collected from the newly introduced area and the potential source area belong to the same part. The samples can be collected from branches or seeds of the plant. The collected samples can be stored in a ventilated and dry place at room temperature. Unlike traditional genetic testing methods, they do not need to be poured into silica gel for preservation, nor do they need to be stored in liquid nitrogen or placed in a refrigerator for low-temperature storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 Cluster diagram of stable isotope content in Solanum serrata branches Figure 2 This is the traceability analysis diagram of the stable isotope content in the branches of Solanum eryngii; Figure 3 This is the discriminant analysis result of the origin of Solanum eryngii branches; Figure 4 This is the cluster diagram of stable isotope content of Solanum erythraea seeds; Figure 5 This is the traceability analysis diagram of the stable isotope content of Solanum eryngii seeds; Figure 6 This is the discriminant analysis result of the origin of Solanum eryngii seeds; Figure 7 is the cluster diagram of stable isotope content of straw; Figure 8 This is the traceability analysis diagram of the stable isotope content in straw; Fig. 9 This is the result of the analysis of the origin of the straw; Fig.10 It is the cross-regional diffusion network of Solanum erythraea. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example 1 Solanum erythrocarpon Solanum rostratum Dund. is a highly invasive annual weed of the Solanum genus of the Solanaceae family. In recent years, newly invasive Solanum spicata has been found in natural grasslands of many banners in Xilin Gol League, Inner Mongolia, and effective prevention and control measures are urgently needed.

[0021] This example provides a method for tracing the spread of invasive alien plants using stable isotopes. The carbon (δ 13 C), nitrogen (δ 15 N), oxygen (δ 18 O), hydrogen (δ 2 H) Stable isotope ratios are used to track the sources and pathways of the spread of Solanum luteum and to analyze and determine the risk areas where Solanum luteum invasion may occur, thereby providing accurate data support for the management and control of its spread, in order to inhibit its further rapid spread.

[0022] This method includes the traceability analysis of Solanum eryngii and the identification of the spread risk of Solanum eryngii.

[0023] 1. Analysis of the origin of Solanum eryngii 1. Plant sample collection 1) Determine the newly introduced area: Based on the national spatiotemporal distribution data of Solanum erythrocarpa, the areas where Solanum erythrocarpa has been newly recorded in the past five years were selected as the newly introduced area.

[0024] 2) It was found that the main crop product adulterated with Solanum luteum was straw. Therefore, the straw purchased by farmers in the newly introduced areas and the remains and seeds of Solanum luteum plants mixed in it were collected as plant samples from the newly introduced areas.

[0025] 3) Conduct field investigations on the sources of straw purchased in the newly introduced areas, collect spatiotemporal data on straw planting in the country, collect spatiotemporal data on the occurrence of Solanum serrata in the country, and obtain potential sources of plant samples from the newly introduced areas.

[0026] 4) Collect Solanum sylvestris and straw from different areas of the potential source area. The collection parts are the same as those for plant samples from the newly introduced areas, and use them as plant samples from the potential source area.

[0027] When collecting plant samples from newly introduced areas and potential source areas, plants without insect eyes and lesions should be selected for sampling, and the collected samples can be stored in a ventilated and dry place at room temperature. According to actual needs, relatively dense sampling points can be planned, for example, straw and Solanum serrata plants from adjacent farmland plots less than 1 km away can be collected, which is conducive to more accurately capturing local differences and helping to improve the accuracy of traceability.

[0028] 2. Sample pretreatment 1) Dust and debris removal: Remove surface pollutants (such as dust and dirt) from newly introduced plant samples and potential source plant samples.

[0029] 2) Drying: After dust and impurities are removed, plant samples from newly introduced areas and potential source areas are placed in a freeze dryer or a constant temperature dryer and dried to constant weight. If a freeze dryer is used for drying, during the drying process, the temperature in the freezing stage is lowered to below the freezing point (-80~-40℃) to freeze the water, ensuring that the structure and biological activity of the sample remain unchanged as much as possible. In the sublimation stage (main drying stage), the sample is heated to -50~-20℃ under vacuum conditions, and the water is directly sublimated from the solid state to the gas state. In order to remove the small amount of remaining water in the sample, secondary drying can be performed, and the temperature is gradually increased to -10~20℃. If a constant temperature dryer is used, the temperature needs to be controlled between 40~60℃ to avoid changes in the isotopic composition of the plant sample due to excessively high temperature.

[0030] 3) Pulverization: The dried plant samples from newly introduced areas and potential source areas should be pulverized using a grinder and then passed through a 100-mesh standard sieve for isotope analysis. Different plant parts should be pulverized separately to prevent cross contamination.

[0031] 4) Sampling: Take 2~3 mg of the sieved sample as a subsample.

[0032] 3. Stable isotope determination The pre-treated sub-samples are subjected to stable isotope determination using a mass spectrometer or an isotope ratio mass spectrometer (IRMS) and the stable isotope ratio of the sub-samples is calculated. The stable isotope ratio includes δ 13 C.δ 15 N, δ 18 O, δ 2 H, unit is ‰.

[0033] When conducting carbon and nitrogen stable isotope detection: first, weigh 2 mg of subsamples using a high-precision balance with an accuracy requirement of up to one millionth of a gram to ensure weighing accuracy; second, place the subsamples in a tin foil boat for sample packaging to prevent the subsamples from being contaminated or lost during the analysis process; then, place the packaged subsamples in the solid sample automatic sampling tray of the elemental analyzer, and ensure that 1 to 2 standard substances are inserted for quality control every 12 subsamples. The subsamples are converted into CO2 and N2 gases through combustion reduction reactions under high temperature conditions, and then enter the isotope ratio mass spectrometer for precise detection. In terms of instrument settings, the combustion tube temperature is set to 950°C, the reduction tube temperature is set to 600°C, the carrier gas is high-purity helium, the reference gas is CO2 and N2, and the oxygen flow rate is set to 40 mL min -1 , oxygen injection time was 70 seconds. The accelerating voltage of the mass spectrometer for carbon isotope analysis was 3992 V, the accelerating voltage for nitrogen isotope analysis was 4230 V, and the magnetic field strength was 3600 mA (C mode) and 2800 mA (N mode), respectively.

[0034] In the detection of hydrogen and oxygen stable isotopes: 2 mg of subsamples were weighed and placed in a silver boat for sample packing, and then placed in the solid sample automatic sampling tray of the element analyzer, and the quality control of the standard material was performed. The hydrogen and oxygen in the subsamples were converted into hydrogen and carbon monoxide gases through high-temperature cracking reactions, and the generated gases entered the isotope ratio mass spectrometer for detection. The cracking furnace temperatures of hydrogen and oxygen were set to 1080°C and 1180°C, respectively, and the helium purge flow rate was 230 mL·min -1 , the reference gases were CO and H2. The accelerating voltage of the mass spectrometer for hydrogen isotope analysis was 4032 V, the accelerating voltage for oxygen isotope analysis was 4230 V, and the magnetic field strength was 820 mA (H mode) and 2800 mA (O mode), respectively.

[0035] 4. Analyze the diffusion source and diffusion path of Solanum eryngii After the stable isotope ratios of the subsamples of Solanum serratum and crop straw collected in the new introduction area and potential source area in the above steps are determined, the data are processed using statistical methods to analyze the diffusion sources and diffusion paths of Solanum serratum. In this embodiment, the stable isotope ratios of the subsamples of the plant samples in the new introduction area and the stable isotope ratios of the subsamples of the plant samples in the potential source area are processed using principal component analysis (PCA). The stable isotope ratio data are clustered using principal component analysis software to reveal the stable isotope characteristics of straw and Solanum serratum from different sources. In this way, the subsamples from different sources can be classified to obtain the diffusion sources of Solanum serratum, and the diffusion paths are obtained based on the road links between the diffusion sources.

[0036] II. Identification of the risk of Solanum eryngii spreading 1. Constructing the diffusion network of Solanum spicatum Based on the traceability results of stable isotopes of Solanum erythrorhizon, combined with the spatial position of its diffusion network nodes, and according to the minimum cost principle of actual straw transportation, the Solanum erythrorhizon diffusion network was constructed using ArcGIS spatial analysis software and Python data analysis tools. By calculating the centrality of different nodes, the high-risk areas in the Solanum erythrorhizon diffusion network were identified; the specific steps include the following steps.

[0037] 1) Identify diffusion network nodes: According to the diffusion sources and diffusion paths of Solanum serrata analyzed in the above steps, determine the diffusion network nodes of Solanum serrata, including straw production sites, logistics transit centers, straw distribution sites, straw markets for transferring straw, and markets or farmers and herdsmen for receiving straw.

[0038] 2) Generate road network links between diffusion network nodes: Since the transportation cost of straw increases with the increase of transportation distance, roads with shorter distances will be given priority in the actual transportation process. Therefore, this scheme uses the nearest neighbor analysis tool of ArcGIS 10.2 to calculate the distance between diffusion network nodes, and uses the nearest facility tool to realize the optimal path analysis between nodes to complete the road network link: ① In order to determine the spatial location of the diffusion network nodes of Solanum serrata, the latitude and longitude of the above nodes are obtained from Google Maps; ② Download the main road data of my country, and use the geographic analysis tool of ArcGIS software to cut out the main roads in the study area; ③ Merge the road network vector data, and use the Arctoolbox data management tool to merge the national highway, expressway, provincial highway, county road, and township road data within the study area into a shapefile file; ④ Create a network dataset, and use the road vector data generated in the above steps in ArcGIS Catalog to create a road network dataset Network Dataset with topological relationship; ⑤ Call the NewClosest under the ArcGIS Network Analyst module of ArcGIS software Facility tool, add road network dataset, use road length as impedance, find the travel cost between nodes, solve the best path and path length between nodes, and generate road network links between diffusion network nodes; 3) Use Python software Networkx package to construct straw trade network based on the diffusion network nodes and road network links.

[0039] 2. Identify areas of risk of spread By analyzing the correlation between the centrality of diffusion network nodes and the distribution frequency of Solanum serrata, the risk areas of Solanum serrata invasion in the straw trade network were identified; the centrality measurement indicators include degree centrality, betweenness centrality and closeness centrality; Degree Centrality D(i) The calculation formula is shown in formula (1): (1); In the formula, d i is the degree of node i, N is the total number of nodes in the network; Betweenness Centrality C(i) The calculation formula is shown in formula (2): (2); In the formula, β ij Indicates the starting node i To the end j The number of links contained in the shortest path, Nis the total number of nodes in the network; Closeness Centrality B(i) The calculation formula is shown in formula (3): (3) In the formula α xy For Node x To Node y The number of all shortest paths, α xy (i) For Node x To Node y And through the node i The number of all shortest paths.

[0040] When the degree centrality, betweenness centrality, and closeness centrality of a diffusion network node are significantly correlated with the distribution frequency of invasive alien plants (P < 0.05), the diffusion network node is judged to be a high-risk invasion area; when one or two of the degree centrality, betweenness centrality, and closeness centrality of a diffusion network node are significantly correlated with the distribution frequency of invasive alien plants, the diffusion network node is judged to be a medium-risk invasion area; when the degree centrality, betweenness centrality, and closeness centrality of a diffusion network node do not show a significant correlation with the distribution frequency of invasive alien plants, the diffusion network node is judged to be a low-risk invasion area.

[0041] In addition, since tracing the spread of invasive plants is a long-term task, a database of the spread sources of alien invasive plants can also be constructed to facilitate subsequent work: including (1) continuously collecting plant samples from all over the country, and establishing an isotope database of sub-samples of plant samples from newly introduced areas and an isotope database of sub-samples of plant samples from potential sources; (2) collecting data on natural environmental factors and human activity factors in newly introduced areas and potential sources. Since these factors directly affect the isotope composition of alien invasive plants, they must be recorded together with the isotope data to establish an environmental factor database; among them, natural environmental factor data include climate, soil type, and water source data of plant sample sampling points in newly introduced areas and potential sources; human activity factor data include land use data, road network density, distance from roads, and human activity footprint index in newly introduced areas and potential sources; (3) collecting the introduction time, distribution area, and spread path of alien invasive plants in various parts of the country, and establishing a historical spread information database. The spread path and speed of the alien invasive plants can be inferred from historical records, which can assist in analyzing the spread source.

[0042] Example 2 Conduct traceability analysis on Solanum sylvestris and the straw that carries it.

[0043] 1) Branches of Solanum luteum: A total of 55 subsamples of Solanum luteum branches of the alien invasive plant were tested for their C, N, O, and H stable isotope contents and ratios, and a principal component analysis (PCA) was used to construct an origin discrimination model, such as Figure 1 The results show that the subsamples collected from potential source areas can be divided into 7 groups. Figure 2 As shown in the figure, the branches of Solanum eryngii intercepted from the cargo transported from the newly introduced area in Inner Mongolia mainly belong to the same group as the potential source cities of Chifeng and Zhangjiakou. One-way ANOVA and PLS-DA were further used to judge the accuracy of the model traceability, with 70% of the samples as the training set and 30% of the samples as the test set. Figure 3 As shown, the results show that the accuracy of the model is 88.24%, indicating that the model has strong stability and can accurately trace the branches of Solanum serrata.

[0044] 2) Solanum luteum seeds: A total of 43 subsamples of the invasive alien plant Solanum luteum seeds were tested for their C, N, O, and H stable isotope contents and ratios, such as Figure 4 As shown in the figure, the analysis results show that the samples of Solanum eryngii seeds collected from the source area can be divided into 6 groups. Figure 5 As shown in the figure, the yellow flower spinulosa seeds intercepted from the cargo transported from the new introduction area in Inner Mongolia belong to the same group as the potential source cities of Chifeng and Zhangjiakou. One-way ANOVA and PLS-DA were further used to judge the accuracy of the model traceability, with 70% of the samples as the training set and 30% of the samples as the test set. Figure 6 As shown, the discrimination results show that the accuracy of the model is 88.24%, indicating that the model has strong stability and can accurately trace the seeds of Solanum serrata.

[0045] 3) Straw: A total of 92 straw subsamples were tested for their C, N, O, and H stable isotope contents and ratios. The PCA-X model was used to analyze the stable isotope contents, such as Figure 7 As shown in Figure 2, the cluster analysis results show that all subsamples of potential sources can be divided into seven groups by analyzing stable isotopes. Figure 8 As shown in Figure 1, the traceability analysis results showed that the straw collected from the newly introduced areas in Inner Mongolia belonged to the same group as the potential source cities of Chifeng, Zhangjiakou, Tongliao and Ulanqab. One-way ANOVA and PLS-DA were further used to determine the accuracy of the model traceability, with 70% of the subsamples as the training set and 30% of the subsamples as the test set. Fig. 9 As shown in the figure, the discrimination results show that the accuracy of the model is 86.84%, indicating that the model has strong stability and can accurately trace the straw.

[0046] The traceability results of straw, Solanum luteum branches and seeds were comprehensively analyzed, and the Chi-square test was used to test whether there were significant differences between the traceability results. The results are shown in Table 1. There was no significant difference in the traceability results of the three types of plant subsamples, indicating that the source of the straw purchased in the newly introduced area was consistent with the source of Solanum luteum, further verifying that inter-regional straw trade activities were the diffusion pathway of Solanum luteum.

[0047] Table 1 The differences in the traceability results of branches, seeds and straw of Solanum erythrorhizon

[0048] Example 3 Conduct a spread risk analysis on Solanum eryngii.

[0049] A total of 9 cities were collected for the collection of branches, seeds and straw samples of Solanum serratum. The straw intercepted in the Qianshao area only came from Zhangjiakou City (Source 1), Ulanqab City (Source 2), Tongliao City (Source 3) and Chifeng City (Source 4), and Solanum serratum only came from Zhangjiakou City and Chifeng City. Since Solanum serratum plants are mixed with straw for diffusion, a straw trade network was constructed based on the principle of minimum transportation cost, which transported straw from the source to the grass market and then to the herders' homes, that is, the Solanum serratum cross-regional diffusion network.

[0050] like Fig.10 As shown in the figure, the results of analyzing the source areas in the straw trade network showed that: there were potential source areas with Solanum serrata distributed in millet fields, such as the source areas in Zhangjiakou and Chifeng, and Solanum serrata plants were intercepted in the downstream grass markets or herdsmen; while there were no potential source areas with Solanum serrata distributed in millet fields, such as the source areas in Tongliao and Ulanqab, and no Solanum serrata plants were intercepted in the downstream grass markets or herdsmen.

[0051] Further analysis of the correlation between the centrality of diffusion network nodes and the occurrence frequency of Solanum erythraea was performed, such as Figure 2 As shown, the results show that among the diffusion network nodes from Chifeng and Zhangjiakou, the degree centrality of the diffusion network nodes D(i) , betweenness centrality C(i) and closeness centrality B(i) The frequency of Solanum lycopersicum distribution showed a significant positive correlation (P < 0.05), that is, the higher the centrality of the node, the higher the frequency of Solanum lycopersicum distribution, indicating that the higher the centrality of the node in the diffusion network, the higher the risk of invasion by Solanum lycopersicum. The diffusion network nodes from Chifeng and Zhangjiakou were judged to be high-risk areas.

[0052] Table 2 Correlation between node centrality and distribution frequency in the diffusion network of Solanum truncatum

[0053] In summary, the analysis of stable isotopes can identify the source of the spread of the invasive plant Solanum luteum in new areas of introduction. The accuracy of the traceability results of straw and Solanum luteum branches mixed in it is high, reaching more than 80%. The traceability results between the three types of plant subsamples were not significantly different, which verified that the straw trade network is the diffusion pathway network of Solanum luteum. In addition, based on the isotope traceability, the diffusion network model constructed by combining the Solanum luteum occurrence data and straw planting data found that the high-risk areas for Solanum luteum invasion are key nodes with high centrality in the diffusion network.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

[0055] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for tracing the spread of invasive plants using stable isotopes, characterized in that: It includes the analysis of the origin of invasive alien plants and the identification of the risk of their spread; The tracing analysis of the alien invasive plants includes the following steps S1-S4; S1. Plant sample collection: S11. Determine the new introduction area; S12. Collect the alien invasive plants and the crop products mixed with the alien invasive plants from the new introduction area as the plant samples from the new introduction area; S13. Collect data to obtain the potential source of the plant samples from the new introduction area; S14. Collect the alien invasive plants and the crop products from the potential source as the plant samples from the potential source; S2, sample pretreatment; S3, stable isotope determination; S4. Analyze the sources and pathways of spread of invasive alien plants; The risk identification of the spread of invasive alien plants includes the following steps P1 and P2; P1, constructing a diffusion network of the invasive alien plant; P11, identifying diffusion network nodes; P12, generating road network links between the diffusion network nodes; P13, constructing a trade network for the crop products based on the diffusion network nodes and the road network links; P2. Identify diffusion risk areas: Identify risk areas for invasion by the invasive alien plants in the trade network of the crop products by analyzing the correlation between the centrality of the diffusion network nodes and the distribution frequency of the invasive alien plants.

2. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 1, characterized in that: The method for determining the new introduction site in step S11 is: based on the national spatiotemporal distribution data of the alien invasive plants, the areas where the alien invasive plants have appeared newly recorded in the past five years are selected as the new introduction sites.

3. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 1, characterized in that: The data collection in step S13 includes: investigating the sources of the agricultural products purchased in the newly introduced areas, collecting the spatiotemporal data of the planting of the agricultural products in the country, and collecting the spatiotemporal data of the occurrence of the alien invasive plants in the country.

4. The method for tracing the spread of invasive plants using stable isotopes according to claim 1, characterized in that: The pre-processing of step S2 includes: S21, dust and debris removal; S22, drying: drying the newly introduced plant samples and the potential source plant samples after dust and impurity removal to constant weight; S23, crushing: crushing the dried plant samples of the newly introduced area and the plant samples of the potential source area, and then sieving; S24. Sampling: Take 2-3 mg of the sieved sample as a subsample.

5. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 1, characterized in that: The step S3 specifically comprises performing stable isotope determination on the pretreated sub-sample to calculate the stable isotope ratio of the sub-sample; the stable isotope ratio includes δ 13 C.δ 15 N, δ 18 O, δ 2 H.

6. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 1, characterized in that: The step S4 specifically includes: using statistical methods to process the stable isotope ratios of the sub-samples of the newly introduced plant samples and the stable isotope ratios of the sub-samples of the plant samples from the potential source, and analyzing the diffusion sources and diffusion paths of the alien invasive plants.

7. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 1, characterized in that: The step P11 is specifically as follows: according to the diffusion source and diffusion path of the alien invasive plant analyzed in step S4, the diffusion network nodes of the alien invasive plant are determined, including the production site of the crop product, the logistics transit center, the distribution site of the crop product, the grass market for transporting the crop product, and the market or farmers and herdsmen who receive the crop product.

8. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 1, characterized in that: In step P2, the centrality measurement indicators include degree centrality, betweenness centrality and closeness centrality; Degree Centrality D(i) The calculation formula is shown in formula (1): （1）； In the formula, d i is the degree of node i, N is the total number of nodes in the network; Betweenness Centrality C(i) The calculation formula is shown in formula (2): （2）； In the formula, β ij Indicates the starting node i To the end j The number of links contained in the shortest path, N is the total number of nodes in the network; Closeness Centrality B(i) The calculation formula is shown in formula (3): （3） In the formula α xy For Node x To Node y The number of all shortest paths, α xy (i) For Node x To Node y And through the node i The number of all shortest paths.

9. The method for tracing the spread of invasive alien plants using stable isotopes according to claim 8, characterized in that: When the degree centrality, the betweenness centrality, and the closeness centrality of the diffusion network node are all significantly correlated with the distribution frequency of the alien invasive plant, the diffusion network node is determined to be a high-risk invasion area; When one or two of the degree centrality, the betweenness centrality, and the closeness centrality of the diffusion network node are significantly correlated with the distribution frequency of the alien invasive plant, the diffusion network node is determined to be a medium-risk area for invasion; When the degree centrality, the betweenness centrality, and the closeness centrality of the diffusion network node do not show a significant correlation with the distribution frequency of the alien invasive plant, the diffusion network node is determined to be a low-risk invasion area.

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