Method and system for simulating source process mechanism of methane emission in paddy field based on stable carbon isotope characteristics

Abstract

The application discloses a paddy field methane emission source process mechanism simulation method and system based on stable carbon isotope characteristics, and through acquisition of multi-source data, input data of carbon isotope is converted into 13 C / 12 C isotope ratio R; the rhizosphere active methanogenic carbon pool is constructed, and is distributed to two types of paths of acetic acid cracking type and hydrogen nutrition type, flux and fractionation are calculated; total produced methane is distributed to three paths of plant-mediated transmission, liquid phase diffusion and bubble escape, oxidation and residual methane isotope of each path are calculated; total emission flux and emission end δ 13 C-CH 4,em The application synchronously simulates methane flux and emission end isotope characteristics, realizes simulation and analysis of the paddy field methane emission source process mechanism, can diagnose methanogenic path contribution, oxidation intensity and transmission path contribution, and provides support for paddy field methane emission mechanism analysis and emission reduction evaluation.

Description

Technical Field

[0001] This invention relates to the field of greenhouse gas technology in agricultural ecosystems, and in particular to a method and system for simulating the source process mechanism of methane emissions from paddy fields based on stable carbon isotope characteristics. Background Technology

[0002] methane ( Methane is a significant short-lived greenhouse gas with a substantial impact on global warming over recent decades. Paddy fields are a crucial source of methane emissions in agro-ecosystems, playing an indispensable role in regional carbon cycles and agricultural greenhouse gas inventories. Accurately elucidating the process mechanisms of methane emissions from paddy fields is of great importance for optimizing agricultural greenhouse gas inventories, evaluating emission reduction measures, and conducting research on regional carbon cycles.

[0003] Methane production primarily occurs in anaerobic paddy soils, typically involving acetic acid cracking-based methanogenesis and hydrogenotrophic methanogenesis. Different methanogenesis pathways exhibit different carbon isotope fractionation characteristics. Methane oxidation mainly occurs in the rice rhizosphere, soil-water interface, or other microaerobic environments with oxygen supply. Because methane oxidation usually preferentially consumes lighter carbon atoms... Residual methane after oxidation The values ​​will change, therefore, methane oxidation directly affects the carbon isotope composition of the methane ultimately released into the atmosphere.

[0004] The main pathways for residual methane emitted into the atmosphere after oxidation include plant-mediated transport, liquid-phase diffusion, and bubble escape. Plant-mediated transport, through the aerenchyma of rice plants, transports methane from the rhizosphere or soil to the atmosphere and is the primary pathway for methane emissions from paddy fields. Liquid-phase diffusion and bubble escape are influenced by water depth, methane accumulation status, soil structure, and disturbance processes. Different emission pathways have different transport efficiencies, oxidation exposure levels, and apparent isotopic fractionation characteristics, thus affecting the final methane isotopic composition at the emission point. By utilizing isotope fractionation and isotope mass conservation characteristics, identifying the contributions of different methanogenesis pathways, oxidation processes, and emission pathways to the characteristics of the final emission source can help explain the intrinsic mechanism of methane emissions from paddy fields.

[0005] However, existing methods for simulating methane emissions from paddy fields primarily focus on flux estimation, which still makes it difficult to further explain whether the seasonal dynamics of methane emissions from paddy fields originate from changes in methane production pathways, enhanced oxidation processes, or changes in emission pathways.

[0006] Therefore, there is an urgent need to establish a system that can unify the processes of methane generation, oxidation, and emission, and continuously track each process. A simulation method for rice paddy methane emission source processes based on isotope ratios. The focus of this method is to obtain isotope data for each process and then use this data and its fractionation characteristics to explain and constrain the intrinsic mechanisms of methane generation, oxidation, and emission pathways in rice paddy methane emission source processes. Summary of the Invention

[0007] To achieve the above objectives, the present invention provides the following technical solution: A simulation method for methane emission source processes in paddy fields based on stable carbon isotope characteristics includes the following steps: Step S1: Obtain the input data required for simulating the methane emission source process mechanism in paddy fields. The input data includes photosynthetic carbon input, soil background carbon input, environmental and management factors, and carbon isotope input data. Among them, the process mechanism of methane emission from paddy fields includes the generation, oxidation and emission of methane from paddy fields; Among them, carbon isotopes are stable carbon isotopes. ; The photosynthetic carbon inputs include observed GPP values, remote sensing estimated GPP, SIF-constrained GPP, ecological model simulated GPP, or other data that can characterize the intensity of rice photosynthesis and recent photosynthetic carbon inputs. GPP stands for Total Primary Productivity of vegetation. Step S2, Isotope Variable Conversion and Internal Calculation Variables: Convert the carbon isotope input data into... The isotope ratio R is used as the isotope calculation variable within the model. The model is constructed using a simulation method based on stable carbon isotope characteristics to model the source process mechanism of methane emissions from paddy fields.

[0008] The isotope ratio R is used as a unified isotope calculation variable within the model for isotope fractionation, mass conservation, and flux-weighted mixing calculations during methane generation, oxidation, emission, and mixing processes.

[0009] Step S3: Construct a rhizosphere active methanogenic carbon library based on photosynthetic carbon input and soil background carbon input, and update its isotope ratios. Specifically, a rhizosphere active methanogenic carbon library was constructed based on photosynthetic carbon input and soil background carbon input. This carbon library was used to characterize active carbon substrates that can be utilized by methanogenic microorganisms and to provide a unified carbon source constraint for subsequent isotopic fractionation of methanogenic pathways. Furthermore, it also includes the following steps: Step S31: Calculate the available fresh carbon input entering the rhizosphere on the same day based on GPP; Step S32: Construct and dynamically update the rhizosphere active methanogenic carbon library; Step S33: Update the isotope ratios of the rhizosphere active methanogenic carbon library; Among them, the isotope ratios of the rhizosphere active methanogenic carbon pool can be obtained from fresh photosynthetic carbon input, soil background carbon input, and the values ​​corresponding to the rhizosphere active methanogenic carbon pool. Isotope ratios are updated through the conservation of isotope mass.

[0010] Step S4: Differentiate between the two types of methanogenic pathways and perform isotopic fractionation on them. Allocate the rhizosphere active methanogenic carbon pool to the two types of methanogenic pathways: acetic acid cracking and hydrogen nutrition. Calculate the methane production flux and isotopic ratio for each type of methanogenic pathway. Furthermore, the allocation ratio of acetic acid cracking-type methanogenesis pathway and hydrogen nutrition-type methanogenesis pathway is determined by one or more factors among soil temperature, pH, moisture state, redox state, organic matter supply, rice growth stage, and field management practices.

[0011] Among them, when pore water dissolves inorganic carbon or CO2 When observing the data, the carbon precursors of the hydrogen-trophic methanogenesis pathway are constrained by dissolved inorganic carbon or CO2 isotope composition: in To stabilize isotopic composition; The acetic acid cracking-type methanogenesis pathway and the hydrogen nutrition-type methanogenesis pathway were respectively assigned methanogenic carbon isotope fractionation coefficients, and the methane production of the two methanogenesis pathways was calculated separately. The isotope ratios are then used to perform flux-weighted mixing based on the methane production fluxes of the two methanogenic pathways to obtain the total methane isotope composition.

[0012] Step S5: Based on the methane production flux of the two types of methanogenic pathways, obtain the total methane production flux and the total methane isotope ratio. Step S6: Distribute the total methane produced to the plant-mediated transport pathway, the liquid-phase diffusion pathway, and the bubble escape pathway; Step S7: Analyze the oxidation processes of rhizosphere, soil-water interface, and bubble path, and calculate the residual methane isotope ratio after oxidation based on oxidative fractionation and isotope mass conservation. For plant-mediated transport pathways, calculate rhizosphere oxidation flux. .

[0013] Furthermore, the rhizosphere oxidation flux can be determined by the rhizosphere methane supply, rhizosphere oxygen supply, rhizosphere maximum oxidation capacity, growth period function, oxygen competition function, temperature function, and pH function.

[0014] The methane oxidation process at the soil-water interface is influenced by factors such as interfacial methane supply, oxygen accessibility, water depth, pH, and soil temperature. The concentration and the maximum oxidation capacity at the soil-water interface are used to determine the concentration.

[0015] Furthermore, when methane isotope observations, bubble oxidation observations, or bubble endmember observations are available, the bubble path oxidation flux can be set. and bubble path oxidation fractionation coefficient The isotope ratio of residual methane after oxidation of the bubble path was calculated according to the isotope mass conservation method.

[0016] Step S8: Calculate the net methane emission flux and the corresponding methane isotope ratios for the three emission pathways; Apparent transport fractionation coefficients are set for plant-mediated transport pathways, liquid-phase diffusion pathways, and bubble escape pathways, which are used to calculate the methane isotope ratios at the emission ends of the corresponding emission pathways. In the simplified implementation, the apparent transport fractionation coefficient of the bubble escape path is set to no additional fractionation. Step S9: Based on the net methane emission fluxes from the three emission pathways and the corresponding methane isotope ratios, perform flux-weighted mixing to obtain the total methane emission flux and the final emission endpoint. ; in, The isotopic composition of emitted methane; After determining the methane isotope ratios at the emission ends of the three pathways, the isotope ratios of methane at the total emission end are weighted and mixed according to the net emission flux, resulting in the final isotope composition of the methane emitted at the emission ends. The isotopic characteristics of methane emission sources from paddy fields obtained from simulations were characterized. These characteristics were correlated with methane flux, pathway contribution, oxidation ratio, and observational constraints. Together, they are used to explain the underlying mechanisms of methane production, oxidation, and transport pathways in paddy fields; Step S10: Based on the contributions of the two types of methanogenic pathways, oxidation flux and oxidation ratio, the contributions of the three emission pathways, and the final emission end... To diagnose the process mechanisms of methane generation, oxidation, and emission pathways in paddy fields; Furthermore, the final emission end This is used to characterize the isotopic features of methane emission sources from paddy fields obtained from model simulations and compare them with observational constraint information to diagnose the contributions of methane generation pathways, oxidation intensity, and emission pathways. Among them, the observation constraint information is the regression intercept.

[0017] This invention also proposes a simulation system for the source process mechanism of methane emissions from paddy fields based on stable carbon isotope characteristics, comprising the following modules: (1) Data on photosynthetic carbon input, soil background carbon input, environmental and management factors, and carbon isotope input are obtained through the data input module; (2) Convert the carbon isotope input data into isotope values ​​using the isotope calculation module. The isotope ratio R is used as the isotope calculation variable within the model for isotope fractionation, mass conservation, and flux-weighted mixing calculations. (3) Construct a rhizosphere active methanogenic carbon library through the methane production module, and calculate the methane production flux and isotope ratio of the two types of methanogenic pathways: acetic acid cracking and hydrogen nutrition. (4) Calculate the rhizosphere oxidation, soil-water interface oxidation and optional bubble path oxidation processes through the methane oxidation module, and calculate the residual methane isotope ratio after oxidation based on isotope mass conservation. (5) Calculate the net emission flux and emission end isotope ratio of the three emission pathways, namely plant-mediated transport, liquid-phase diffusion and bubble escape, using the methane emission module; (6) Through the result mixing and mechanism diagnosis module, the net emission flux and isotope ratio of the three emission pathways are mixed by flux weighting, and the total methane emission flux and the final emission end are output. Diagnostic results regarding the mechanisms of methane generation, oxidation, and emission pathways; (7) Through the observation constraint and parameter calibration module, using methane flux, methane concentration, , , pore water, methane, oxygen One or more of the following observation information—water layer depth, Eh, or path separation—are used to calibrate, validate, and assess the uncertainty of model parameters and simulation results.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: First, this invention establishes a stable carbon isotope tracking system for the entire process of methane generation, oxidation, and emission in paddy fields. It constructs a source mechanism for methane emission from paddy fields by analyzing the methane generation, oxidation, and emission processes, and uniformly adopts [the appropriate carbon isotope] within the model. The isotope ratio R is used as the core calculation variable, replacing the traditional The direct linear mixing approach achieves strict consistency and numerical stability in isotope calculations by standardizing the entire chain of methanogenic fractionation, residual oxidation mass conservation, and multi-path flux weighted mixing. Simultaneously, a flux-isotope coupled simulation architecture is employed to synchronously output methane emission flux and emission end-point data. By incorporating multidimensional observation information on concentration, flux, and isotopic characteristics into a unified diagnostic framework, this approach effectively solves the problem of the separation between "flux estimation" and "isotopic analysis" in traditional models, and significantly improves the explanatory power and comprehensive diagnostic accuracy of the intrinsic mechanism of methane emissions from paddy fields.

[0019] Secondly, an innovative dynamic updating mechanism for the rhizosphere active methanogenic carbon pool was constructed, integrating fresh carbon input from photosynthesis and background organic carbon input from the soil into the methanogenic substrate supply system. The evolution of the carbon pool's isotopic composition was tracked in real time using a mass conservation equation, achieving a quantitative correlation between photosynthetic carbon conversion efficiency and methanogenic substrate supply. Furthermore, for the first time, a model of methanogenesis in paddy fields explicitly distinguished between acetic acid cracking and hydrogen nutrient pathways. By setting pathway allocation functions, comprehensive efficiency coefficients, and isotopic fractionation coefficients respectively, the methane production flux and isotopic composition of the two pathways were independently calculated. This enabled a quantitative attribution of changes in the methanogenic pathway structure to the isotopic characteristics of emission sources, providing a key mechanism constraint for analyzing the crop-soil-microbe carbon coupling process and methanogenic pathway conversion.

[0020] Furthermore, a three-tiered oxidation module was explicitly constructed, comprising rhizosphere oxidation, soil-water interface oxidation, and optional bubble pathway oxidation. The isotope ratios of residual methane at each oxidation interface were calculated using the law of conservation of isotope mass. Through dynamic output of oxidation flux and oxidation ratio, quantitative diagnosis of the effect of oxidation intensity changes on methane flux reduction and emission-end isotope shift was achieved. Simultaneously, the three emission pathways—plant-mediated transport, liquid-phase diffusion, and bubble escape—were modularly separated, and the net emission flux, apparent transport fractionation coefficient, and emission-end isotope ratios for each pathway were calculated. A flux-weighted mixture model was used to quantitatively identify the impact of different transport pathways on the final... The contribution share provides an independent and verifiable technical means for analyzing the emission pathway structure.

[0021] In addition, a multi-source observation data assimilation interface was established to support methane flux, concentration, and The model's parameters are dynamically calibrated and validated through a combined constraint mechanism of ground-based continuous observations, Keeling plot / Miller-Tans source apportionment results, path separation observations, and indoor culture experimental data. This mechanism utilizes a two-way feedback system of observation and simulation. The final emission data from the model output is then used as the constraint. Constraints of atmospheric isotope observation source analysis By conducting direct comparisons and quantifying simulation accuracy using indicators such as linear correlation, R², RMSE, and seasonal transition time, an isotopic bridge was established between the process model and atmospheric observations, significantly enhancing the model's verifiability, data adaptability, and regional-scale application capabilities.

[0022] Finally, this invention expands the application boundaries of the method, which can be widely applied to scenarios such as isotope characteristic simulation of methane emission sources in paddy fields, diagnosis of generation-oxidation-emission process mechanisms, identification of multi-path contributions, evaluation of the effectiveness of agricultural emission reduction measures, constraint of regional emission uncertainty, optimization of greenhouse gas inventories, and verification of carbon cycle models. It forms a complete technical chain from field process analysis to regional scale application, providing a scientific basis for the formulation of methane emission reduction strategies in paddy fields and the compilation of agricultural greenhouse gas inventories. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a flowchart of the overall process mechanism simulation method for methane emission source process in paddy fields based on stable carbon isotope characteristics as described in this invention. Figure 2 This is a flowchart of the methane generation module and its carbon isotope fractionation calculation according to the present invention; Figure 3 This is a flowchart of the methane oxidation module and the calculation of the mass conservation of residual methane isotopes after oxidation, as described in this invention. Figure 4 This is a flowchart illustrating the calculation of the methane isotope composition of the three methane emission paths and the final emission point as described in this invention. Figure 5 This is a flowchart of the observation data constraints and model parameter calibration process described in this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] Combined with appendix Figure 1-5 This invention provides a method for simulating the source process mechanism of methane emissions from paddy fields based on stable carbon isotope characteristics, comprising the following steps: Step S1: Obtain the input data required for carbon isotope simulation of methane production, oxidation and emission processes in paddy fields. The input data includes photosynthetic carbon input, soil background carbon input, environmental and management factors, and carbon isotope input data. Among them, the process mechanism of methane emission from paddy fields includes the generation, oxidation and emission of methane from paddy fields; refer to Figure 1 The overall flowchart of the simulation method for the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics is given in the figure. The photosynthetic carbon inputs include observed GPP values, remote sensing estimated GPP, SIF-constrained GPP, ecological model simulated GPP, or other data that can characterize the intensity of rice photosynthesis and recent photosynthetic carbon inputs. GPP stands for Total Primary Productivity of vegetation. The soil background carbon input includes soil organic matter, straw, root residues, root exudates, soil soluble organic carbon, or other organic substrate supply. The environmental and management factors include soil temperature, water level or water depth, pH, redox state, ammonium nitrogen concentration, rice growth period, irrigation and drainage measures, fertilization, straw return to the field or other field management measures. The carbon isotope input data includes the isotopic composition of available fresh carbon input from the rhizosphere. Soil isotopic composition Isotopic composition of pore water Carbon dioxide isotope composition Methane isotope composition Or other isotopic data relating to the carbon source, substrate, and methane composition, wherein the isotopes are carbon isotopes.

[0026] Step S2, Isotope Variable Conversion and Internal Calculation Variables: Convert the carbon isotope input data into... The isotope ratio R is used as the isotope calculation variable within the model. The model is constructed using a simulation method based on stable carbon isotope characteristics to model the source process mechanism of methane emissions from paddy fields.

[0027] The isotope ratio R is used as a unified isotope calculation variable within the model for isotope fractionation, mass conservation, and flux-weighted mixing calculations during methane generation, oxidation, emission, and mixing processes.

[0028] Furthermore, isotopic composition Value and Isotope ratios R can be converted between each other according to the general definition of stable isotopes: ; ; in, For VPDB standard Ratio; the above transformation is used for variable transformation between model inputs and outputs; within the model, R is preferentially used for mass conservation and flux-weighted mixing to avoid direct manipulation. The values ​​are subjected to unreasonable linear mixing.

[0029] Appendix Figure 1 The middle gives Input conversion After the ratio R is calculated, R is used as the isotope calculation variable within the model to participate in the calculations of the methane generation module, methane oxidation module, and methane emission module, respectively.

[0030] Step S3: Construct a rhizosphere active methanogenic carbon library based on photosynthetic carbon input and soil background carbon input, and update its isotope ratios. Specifically, a rhizosphere active methanogenic carbon library was constructed based on photosynthetic carbon input and soil background carbon input. This carbon library was used to characterize active carbon substrates that can be utilized by methanogenic microorganisms and to provide a unified carbon source constraint for subsequent isotopic fractionation of the methanogenic pathway.

[0031] Furthermore, it also includes the following steps: Step S31: Calculate the available fresh carbon input entering the rhizosphere on the same day based on GPP: ; in, For the input of available fresh carbon into the rhizosphere that day, For the total primary productivity of the day, This represents the proportion of GPP converted into rhizosphere active substrates. This is the correction factor for the variety or plant.

[0032] Furthermore, It can be obtained in the following way: GPP can be obtained through remote sensing inversion, based on NDVI / EVI or SIF data from satellites such as MODIS and Sentinel, combined with light energy utilization models (such as EC-LUE and VPM); or by using flux tower observations, directly measuring net ecosystem exchange (NEE) through the eddy covariance method, and obtaining GPP by combining the respiration component; or by using crop growth models, such as WOFOST and ORYZA2000, which simulate crop photosynthesis processes to output GPP.

[0033] The proportion of GPP converted to rhizosphere active substrates is a model parameter that can be obtained through model calibration, such as by inverting and optimizing rhizosphere deposition rates or soil respiration data observed in the field; it can also be obtained through isotope tracing experiments, based on... Pulse labeling can be used to track the proportion of photosynthetic carbon deposited in the rhizosphere; alternatively, it can be obtained from literature / tables by referencing published assimilation coefficients based on crop type (rice / wheat / maize, etc.), with commonly used values ​​ranging from approximately 0.2 to 0.5.

[0034] This is a correction coefficient for varieties or plants, belonging to correction parameters. It can be determined through field comparison experiments based on differences in root exudate amount, root-shoot ratio, etc. among different varieties; or a default value can be set according to a variety parameter database (such as the IRRI rice variety library), and then calibrated and optimized based on local observations.

[0035] Step S32: Construct and dynamically update the rhizosphere active methanogenic carbon library; Specifically, let the rhizosphere active methane-producing carbon library be... Its dynamic update can be represented as: ; in, Provides background substrates for the formation of soil organic matter, straw, root residues or other organic substrates. This refers to the loss or turnover coefficient of the activated carbon pool in the non-methanogenic direction. The coefficient for the conversion of the activated carbon library into a direct methanogenic precursor; in, The initial value can be set based on field measurements or literature estimates; t represents time, and its unit can be hours or days, etc.

[0036] There are several methods to obtain organic carbon (DOC). It can be obtained through the soil organic matter decomposition rate constant method, which is calculated based on the soil organic carbon pool (SOC) and decomposition kinetic parameters; or through the input amount of straw / root residues, which is estimated based on the crop biomass allocation coefficient and residue amount; or through field measurement, where soil samples collected in the field can be measured to extract organic carbon (DOC) or microbial biomass carbon (MBC). Values ​​can be obtained by consulting tables or literature, such as referring to historical tables of paddy field soil carbon turnover or related literature; they can also be obtained through model calibration: that is, using field methane emission flux observation data and inverting it through optimization algorithms (such as MCMC, least squares method); or they can be obtained through isotope tracing experiments, that is, through... The markers track the destination of carbon and distinguish between the proportion of carbon loss that is produced by methanogenesis and that is not. Values ​​can be obtained by looking up tables or literature, such as referring to historical tables of methanogenic substrate conversion efficiency or relevant literature; they can also be obtained by correlating with the activity of methanogenic bacteria and establishing response functions based on environmental factors such as soil redox potential (Eh), temperature, and pH; or they can be obtained by constructing and calibrating models and then inverting them by combining observation data on methane production rates.

[0037] Step S33: Update the isotope ratios of the rhizosphere active methanogenic carbon library; Specifically, the isotopic ratios of the rhizosphere active methanogenic carbon library are updated according to mass conservation: ; in, For rhizosphere active methane-producing carbon pool isotope ratio, The isotopic ratio of fresh photosynthetic carbon input. The isotopic ratio of the soil background carbon input.

[0038] It can be obtained in the following ways, such as direct measurement, that is, by collecting rice aboveground / root samples and measuring the plant tissue using elemental analysis-stable isotope ratio mass spectrometry (EA-IRMS). Then convert it to the corresponding R value; The analysis can be performed by collecting control soil or deep soil samples from areas where rice has not been planted, and then measuring the results using EA-IRMS. get; It is evident that the isotopic ratios of the rhizosphere active methanogenic carbon pool can be obtained using fresh photosynthetic carbon input, soil background carbon input, and the values ​​corresponding to the rhizosphere active methanogenic carbon pool. Isotope ratios are updated through the conservation of isotope mass.

[0039] Furthermore, the rhizosphere active methanogenic carbon pool can also be determined by the input of available fresh photosynthetic carbon into the rhizosphere, the supply of soil background organic substrates, carbon pool turnover loss, and the conversion process to direct methanogenic substrates; available fresh photosynthetic carbon input is determined by one or more of GPP, rhizosphere allocation ratio, and plant correction factor.

[0040] As attached Figure 2 As shown, after constructing the rhizosphere active methanogenic carbon library based on photosynthetic carbon input and soil background carbon input, two types of methanogenic pathways, namely acetic acid cracking and hydrogen nutrition, were further distinguished.

[0041] Step S4: Differentiate between the two types of methanogenic pathways and perform isotopic fractionation on them. Allocate the rhizosphere active methanogenic carbon pool to the two types of methanogenic pathways: acetic acid cracking and hydrogen nutrition. Calculate the methane production flux and isotopic ratio for each type of methanogenic pathway. Specifically, the rhizosphere active methanogenic carbon pool is allocated to two types of direct methanogenic precursors: acetic acid cracking precursors and hydrogen nutrition precursors. ; ; in, The carbon flux supplied to the acetic acid pyrolysis precursor cell. The carbon flux supplied to the hydrogen-nutritive precursor pool. The proportion allocated to the acetic acid cleavage pathway.

[0042] in, Instead of being used as a daily-free fitting parameter, it is treated as a function controlled by environmental factors: ; in, Soil temperature, pH represents acidity / alkalinity, W represents moisture state, Eh represents redox state, OM represents organic matter or substrate supply state, Stage represents rice growth period, and Management represents field management measures.

[0043] The fluxes of the two types of methanogenesis can be expressed as: ; ; ; in, The flux generated from the cracking of acetic acid into methane For hydrogen-nutritive methane generation flux, For the total methane flux, and These are the combined effective coefficients for acetic acid cracking and hydrogen nutrition-based methanogenesis, respectively. Furthermore, and This can be obtained from historical tables or through model calibration based on field observation data. Given initial values, utilize... The observation distinguishes the relative contributions of the two pathways, that is, the contribution ratio of acetic acid cracking and hydrogen nutrition. This is achieved using methane production rate observation data and joint calibration through optimization algorithms (such as MCMC). and .

[0044] Furthermore, the isotopic ratios of acetic acid cracking-type and hydrogen-trophic methanogenic precursors inherit from the rhizosphere active methanogenic carbon library. The isotope ratios are as follows: ; ; in, These are the isotopic ratios of acetic acid cracking-type methanogenic precursors. The isotopic ratio of hydrogen-trophic methanogenic precursors; Furthermore, when pore water dissolves inorganic carbon, CO2, or other inorganic carbon components... When observing the data, the isotopic composition of inorganic carbon, CO2 or other inorganic carbon components dissolved in the pore water is used to constrain the carbon precursor isotope ratios of hydrogen trophic methanogenesis pathways. Specifically, when porous water dissolves inorganic carbon or CO2... When observing data, the ratio of dissolved inorganic carbon or CO2 isotopes should be used preferentially. or Carbon precursors constraining the hydrogen-trophic methanogenesis pathway: or .

[0045] Furthermore, the acetic acid cracking-type methanogenesis pathway and the hydrogen nutrition-type methanogenesis pathway are respectively configured with methanogenic carbon isotope fractionation coefficients, and the methane production of the two methanogenesis pathways is calculated respectively. The isotope ratios are then used to perform flux-weighted mixing based on the methane production fluxes of the two methanogenic pathways to obtain the total methane isotope composition.

[0046] Specifically, the fractionation coefficients for acetic acid cracking and hydrogen nutrition-based methanogenesis are respectively... and The isotope ratios of methane produced by the two pathways are as follows: ; ; Among them, the fractionation coefficients of acetic acid cracking and hydrogen nutrition-type methanogenesis are... and This can be obtained through historical data or experimental calibration; Step S5: Based on the methane production flux of the two types of methanogenic pathways, obtain the total methane production flux and the total methane isotope ratio. The total methane isotope ratio produced is: ; Accordingly, the total methane isotope composition produced is as follows: ; The total methane flux produced is: ; By using the steps described above, isotope ratios and fractionation characteristics can be used to distinguish the contributions of two types of methanogenesis pathways to the production of terminal methane, thus providing constraints for explaining the methanogenesis mechanism.

[0047] Furthermore, the allocation ratio of acetic acid cracking-type methanogenesis pathway and hydrogen nutrition-type methanogenesis pathway is determined by one or more factors among soil temperature, pH, moisture state, redox state, organic matter supply, rice growth stage, and field management practices.

[0048] Step S6: Distribute the total methane produced to the plant-mediated transport pathway, the liquid-phase diffusion pathway, and the bubble escape pathway; Furthermore, the oxidation module receives the total methane flux output from the generation module. and the total methane isotope ratio Before entering the oxidation process, the total methane produced can be distributed to three potential emission pathways: ; ; ; in, , , These are the initial fluxes for three potential emission pathways: plant-mediated transport, liquid-phase diffusion, and bubble escape. in, , and The potential allocation ratios for the three pathways—plant-mediated transport, liquid-phase diffusion, and bubble escape—satisfy the following: ; The isotopic ratios before oxidation or transport via three potential pathways—plant-mediated transport, liquid-phase diffusion, and bubble escape—are as follows: , , All inherit the isotope ratios of the total methane produced: .

[0049] Step S7: Analyze the oxidation processes of rhizosphere, soil-water interface, and bubble path, and calculate the residual methane isotope ratio after oxidation based on oxidative fractionation and isotope mass conservation. Combined with appendix Figure 3 The oxidation process can be analyzed separately for each of the three pathways; Specifically, for plant-mediated transport pathways, the rhizosphere oxidation flux is calculated. In a preferred embodiment, the rhizosphere oxidation flux can be determined by the rhizosphere methane supply, rhizosphere oxygen supply, rhizosphere maximum oxidation capacity, growth period function, oxygen competition function, temperature function, and pH function.

[0050] Furthermore, the residual methane isotope composition after oxidation is calculated based on the mass conservation relationship between the methane flux before oxidation, the methane isotope ratio before oxidation, the oxidized methane flux, and the oxidized methane isotope ratio. The rhizosphere oxidation flux satisfies: ; The rhizosphere oxidative fractionation coefficient is The ratio of methane isotopes consumed by rhizosphere oxidation is: ; The residual methane isotope ratio after rhizosphere oxidation is calculated based on the law of conservation of mass: ; The net flux entering the plant-mediated transport pathway after rhizosphere oxidation is: ; For the liquid phase diffusion path, calculate the oxidation flux at the soil-water interface. The soil-water interface oxidation flux can be determined by interfacial methane supply, oxygen accessibility, water depth, pH, and soil temperature. The concentration and the maximum oxidation capacity at the soil-water interface are jointly determined, and the following conditions must be met: ; The oxidative fractionation coefficient at the soil-water interface is The methane isotope ratio consumed by oxidation at the soil-water interface is: ; The residual methane isotope ratio after oxidation at the soil-water interface is calculated based on the law of conservation of mass: ; The net flux into the liquid phase diffusion path after oxidation at the soil-water interface is: ; Since the bubble escape path is an optional setting, it can be simplified to not undergo significant oxidation: ; ; in, This represents the net flux into the bubble escape path. The residual methane isotope ratio corresponding to the bubble escape path; Furthermore, when methane isotope observations, bubble oxidation observations, or bubble endmember observations are available, the bubble path oxidation flux can be set. and bubble path oxidation fractionation coefficient The isotope ratio of residual methane after oxidation of the bubble path was calculated according to the isotope mass conservation method.

[0051] Rhizosphere oxidation ratio Oxidation ratio at the soil-water interface and total oxidation ratio It can be used as a diagnostic parameter output for the model: ; ; ; The oxidation ratio is not a separately set empirical parameter, but is calculated from oxidation flux and pathway flux. It can be used to explain the variation in methane oxidation intensity under different water management, oxygen supply, or growth stages.

[0052] Step S8: Calculate the methane emission flux and corresponding methane isotope ratios for the three emission pathways; Apparent transport fractionation coefficients are set for plant-mediated transport pathways, liquid-phase diffusion pathways, and bubble escape pathways, which are used to calculate the methane isotope ratios at the emission ends of the corresponding emission pathways. Furthermore, in the simplified embodiment, the apparent transport fractionation coefficient of the bubble escape path is set to no additional fractionation.

[0053] The emission module receives the methane flux and its isotope ratios entering the three emission pathways after oxidation. The net methane emission flux from the three pathways is: ; ; ; in, , , These represent methane emission fluxes via the plant-mediated pathway, the liquid-phase diffusion pathway, and the bubble escape pathway, respectively. The total methane emission flux is: ; Introducing plant-mediated pathways to preserve apparent transport fractionation coefficients The methane isotope ratios emitted via the plant-mediated pathway can be obtained as follows: ; Introducing a liquid-phase diffusion path preserves the apparent transport fractionation coefficient The methane isotope ratios emitted via the liquid-phase diffusion path can be obtained as follows: ; In a simplified implementation, the bubble escape path does not introduce additional transport fractionation; that is, the apparent transport fractionation coefficient of the bubble escape path is set to 1. Therefore, the net methane isotope ratio emitted by the bubble escape path is: ; ; In another implementation, the apparent transport fractionation coefficient of the bubble escape path can be preserved based on bubble path observation. The net methane isotope ratio emitted through the bubble escape path can be obtained as follows: .

[0054] Step S9: Based on the net methane emission fluxes from the three emission pathways and the corresponding methane isotope ratios, perform flux-weighted mixing to obtain the total methane emission flux and the final emission endpoint. ; Combined with appendix Figure 4-5 As shown, after determining the methane isotope ratios at the emission ends of the three pathways, the total methane isotope ratio at the emission end is... Weighted blending by net emission flux: ; The isotopic composition of the methane emitted at the final emission point is as follows: ; Should The isotopic composition of emitted methane is one of the core outputs of this invention, characterizing the simulated isotopic features of methane emission sources from paddy fields. This value is not simply used to output isotopic data, but is related to methane flux, pathway contribution, oxidation ratio, and observation constraints. Together, they are used to explain the underlying mechanisms of methane production, oxidation, and transport pathways in paddy fields.

[0055] Step S10: Based on the contributions of the two types of methanogenic pathways, oxidation flux and oxidation ratio, the contributions of the three emission pathways, and the final emission end... To diagnose the process mechanisms of methane generation, oxidation, and emission pathways in paddy fields; Furthermore, the final emission end This is used to characterize the isotopic features of methane emission sources from paddy fields obtained from model simulations and compare them with observational constraint information to diagnose the contributions of methane generation pathways, oxidation intensity, and emission pathways.

[0056] The observational constraint information involves using multi-source observational data to constrain parameters and process quantities. The observational data includes GPP observations or estimates, methane flux observations, methane concentration observations, and so on. Continuous ground observation, multi-altitude methane concentration and Observations, Keeling plots or Miller-Tans source resolution results, path endmembers Observation, pore water, methane, oxygen One or more of the following: water depth, Eh, soil temperature, results from indoor culture experiments or pathway separation experiments; The observation constraint information is: .

[0057] Specifically, when methane concentration and During observation, observation constraints can be obtained through a Keeling plot. : ; The regression intercept; in, To observe the isotopic composition of atmospheric methane, To observe methane concentration, 'a' represents the regression slope.

[0058] When path-separated observations are available, path contributions can be constrained using the following flux-weighted isotope mixing relation: ; in, , and The contribution ratios of plant-mediated, liquid-phase diffusion, and bubble escape pathways are respectively. , and The isotopic composition is from the emission ends of the three pathways. This refers to residual terms caused by observation errors, external sources, or processes not explicitly expressed.

[0059] This invention outputs the model With observation constraints By comparing and verifying the results, and combining the contributions of two types of methanogenesis pathways, oxidation ratios, and emission pathways, it was determined that the isotopic changes at the emission end mainly originated from changes in methanogenesis pathways, enhanced oxidation processes, or changes in the contribution of transport pathways, thereby achieving a diagnosis of the mechanism of methane emission processes in paddy fields.

[0060] The contributions from the two types of methanogenic pathways include the methane production flux and isotope ratios of the two pathways; the contributions from the three emission pathways include the net methane emission flux and the corresponding emitted methane isotope ratios of the three emission pathways.

[0061] This invention also proposes a simulation system for the source process mechanism of methane emissions from paddy fields based on stable carbon isotope characteristics, comprising the following modules: (1) Data on photosynthetic carbon input, soil background carbon input, environmental and management factors, and carbon isotope input are obtained through the data input module; (2) Convert the carbon isotope input data into isotope values ​​using the isotope calculation module. The isotope ratio R is used as the isotope calculation variable within the model for isotope fractionation, mass conservation, and flux-weighted mixing calculations. (3) Construct a rhizosphere active methanogenic carbon library through the methane production module, and calculate the methane production flux and isotope ratio of the two types of methanogenic pathways: acetic acid cracking and hydrogen nutrition. (4) Calculate the rhizosphere oxidation, soil-water interface oxidation and optional bubble path oxidation processes through the methane oxidation module, and calculate the residual methane isotope ratio after oxidation based on isotope mass conservation. (5) Calculate the net emission flux and emission end isotope ratio of the three emission pathways, namely plant-mediated transport, liquid-phase diffusion and bubble escape, using the methane emission module; (6) The result mixing and mechanism diagnosis module is used to perform flux-weighted mixing of the net emission fluxes and isotope ratios of the three emission pathways, and output the total methane emission flux and the final emission end. Diagnostic results regarding the mechanisms of methane generation, oxidation, and emission pathways; (7) Through the observation constraint and parameter calibration module, using methane flux, methane concentration, , , pore water, methane, oxygen One or more of the following observation information—water layer depth, Eh, or path separation—are used to calibrate, validate, and assess the uncertainty of model parameters and simulation results.

[0062] Furthermore, the output of the simulation method / system may include the following parameters: Total methane production flux ; Ethylene cracking methane production flux Hydrogen-nutritive methane production flux Total methane isotope composition Rhizosphere oxidation flux soil-water interface oxidation flux ; Bubble path oxidation flux methane emission flux via plant-mediated pathway and its emission end methane isotope composition Methane emission flux via liquid-phase diffusion pathway and its emission end methane isotope composition Methane emission flux via bubble escape pathway and its emission end methane isotope composition Total methane emission flux The carbon isotopic composition of methane emitted at the final emission point. Rhizosphere oxidation ratio, soil-water interface oxidation ratio, and total oxidation ratio; contribution ratios of three pathways: plant-mediated, liquid-phase diffusion, and bubble escape; diagnostic results of methane production, oxidation, and emission pathways in paddy fields; parameter uncertainty and simulation result uncertainty range.

[0063] Furthermore, the present invention applies the method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics to the simulation of isotope characteristics of methane emission sources from paddy fields, diagnosis of the process mechanism of methane generation, oxidation, and emission from paddy fields, identification of the contribution of methane emission pathways from paddy fields, evaluation of agricultural methane emission reduction measures, uncertainty constraints on regional paddy field methane emissions, optimization of greenhouse gas inventories, or verification of carbon cycle models.

[0064] Furthermore, methane emissions from rice paddies can also be monitored based on site observations. Simulations were conducted using a rice paddy observation station as an example to obtain data on GPP, soil temperature, water depth, pH, Eh, and other parameters during the rice growing season. Rice growth period, field management practices, methane flux, methane concentration and Continuous ground-based observation data; further acquisition of fresh photosynthetic carbon, soil background carbon, dissolved inorganic carbon or CO2 in pore water. data.

[0065] First, Input data converted Isotope ratio R. Then, a rhizosphere active methanogenic carbon library was constructed based on GPP and soil background carbon input, and the isotopic composition of the carbon library was calculated. Subsequently, the carbon library was assigned to acetic acid cracking and hydrogen nutrient methanogenic pathways, and the methane production flux and its isotopic composition for each pathway were calculated. The total methane production flux and the production-end isotopic composition were obtained by flux-weighted mixing.

[0066] Furthermore, the total methane produced is distributed across three pathways: plant-mediated transport, liquid-phase diffusion, and bubble escape. Rhizosphere oxidation is calculated for the plant-mediated pathway, soil-water interface oxidation is calculated for the liquid-phase diffusion pathway, and direct escape or optional oxidation processes are selected for the bubble escape pathway based on actual needs. The residual methane isotope composition after oxidation in each pathway is calculated based on oxidative fractionation and mass conservation.

[0067] Finally, the methane flux at the emission ends of the three emission pathways was calculated and The total methane emission flux and final emission point were obtained through flux-weighted mixing. This result can be compared with that obtained through Keeling plot or path separation. Comparative verification was conducted; by further comparing the contributions of the two methanogenic pathways, oxidation ratios, and pathway contributions, the emission end could be determined. The change is primarily driven by which type of process among changes in methanogenesis pathways, oxidation processes, or transport pathways.

[0068] Furthermore, based on parameter calibration from path separation observations, methane flux and selectable path endmembers can be obtained for plant-mediated transport, liquid-phase diffusion, and bubble escape pathways at paddy field sites equipped with plant retention / removal boxes, diffusion boxes, bubble collection devices, or other path separation observation conditions. data.

[0069] The plant-mediated pathway observation results were used to constrain the plant-mediated transport ratio, the apparent fractionation coefficient of plant transport, and rhizosphere oxidation-related parameters; the liquid-phase diffusion pathway observation results were used to constrain the diffusion flux, the soil-water interface oxidation ratio, and the apparent fractionation coefficient of diffusion; and the bubble escape flux, the bubble path fractionation coefficient, and the optional bubble path oxidation parameters were constrained using the bubble collection device observation results.

[0070] By comparing the flux of the three paths simulated by the model and Based on observations, the model path allocation parameters and fractionation parameters are calibrated to improve the final emission level. The simulation accuracy was improved, and the contribution of different emission pathways to the isotopic characteristics of paddy field emission sources was analyzed.

[0071] Furthermore, based on methane concentration and Observations were conducted to verify source characteristics, in areas with varying methane concentrations and Ground-based continuous observation stations in paddy fields were used to invert the isotopic characteristics of methane emission sources from paddy fields using the Keeling plot method, the Miller-Tans method, or the mass balance method. .

[0072] In actual observation, the final emission output of the model can be used. With observation constraints Compare the results and calculate the linear correlation and R-squared. 2 Indicators such as RMSE, bias, and seasonal transition time are used to verify the model's ability to characterize the seasonal variations of methane emission source isotopes in paddy fields. When the model can reproduce these parameters well... During seasonal variations, further analysis was conducted on the contributions of acetic acid cracking and hydrogen nutrient-based methanogenesis, the rhizosphere oxidation ratio, the soil-water interface oxidation ratio, and the contributions of plant-mediated, liquid-phase diffusion, and bubble escape pathways to determine the observed levels. What type of process primarily drives change?

[0073] Furthermore, it can also achieve simplified applications under conditions of insufficient constraint information. In areas lacking complete path separation observations or indoor culture experimental data, prior ranges for methanogenic pathway proportions, methanogenic fractionation coefficients, oxidation proportions, path contribution proportions, and apparent transport fractionation coefficients can be set based on existing site observations, historical observations, literature, or experience from similar areas.

[0074] Based on this, using readily available data such as GPP, soil temperature, moisture status, and rice growth stage to drive the model, methane flux and The application provides preliminary simulation results and simultaneously outputs the uncertainty range of the simulation results. This simplified application can still be used to determine the relative contributions of different processes to the isotopic characteristics of emission sources, without limiting isotopic simulation to a single numerical prediction.

[0075] Furthermore, it can be used to evaluate and apply emission reduction measures. For paddy field management measures such as continuous flooding, intermittent irrigation, mid-season field drying, pre-harvest drainage, straw return to the field, fertilizer regulation, or variety differences, corresponding water status, substrate supply, oxidation conditions, and plant-mediated transport parameters can be set to simulate methane production flux, oxidation flux, emission pathway contribution, and final emission end under different measures. change.

[0076] By comparing the total methane emission flux under different management measures, The study investigated changes in oxidation ratio and pathway contribution to assess the impact of different measures on methane emission processes and isotopic characteristics of emission sources in paddy fields. For example, when a certain water management measure leads to a decrease in methane flux and emission source... When the weight increases, the model diagnostic results can be used to determine whether the change is mainly caused by enhanced oxidation, altered methanogenesis pathways, or changes in the contribution of plant-mediated transport.

[0077] In summary, this invention discloses a method and system for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics. By acquiring multi-source data, the carbon isotope input data is converted into... Isotope ratio R; construct the rhizosphere active methane-producing carbon pool and allocate it to two pathways: acetic acid cracking and hydrogen nutrition, calculating fluxes and fractionation; allocate the total produced methane to three pathways: plant-mediated transport, liquid-phase diffusion, and bubble escape, calculating oxidation and residual methane isotopes for each pathway; obtain the total emission flux and emission endpoints through flux-weighted mixing. This invention simultaneously simulates methane flux and emission-end isotopic characteristics, enabling the diagnosis of methanogenic pathway contributions, oxidation intensity, and transport pathway contributions, thus providing support for the analysis of methane emission mechanisms in paddy fields and the assessment of emission reduction.

[0078] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of this application.

[0079] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

Claims

1. A method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics, characterized in that, Includes the following steps: S1. Obtain the input data required for simulating the source process mechanism of methane emission from paddy fields. The input data includes photosynthetic carbon input, soil background carbon input, environmental and management factors, and carbon isotope input data. S2. Convert carbon isotope input data to... The isotope ratio R is used as the isotope calculation variable within the model; S3. Construct a rhizosphere active methanogenic carbon library based on photosynthetic carbon input and soil background carbon input, and update its isotope ratios. S4. Differentiate between two types of methanogenic pathways and perform isotopic fractionation on them. Allocate the active rhizosphere methanogenic carbon pool to two types of methanogenic pathways: acetic acid cracking and hydrogen nutrition. Calculate the methane production flux and isotopic ratio for each type of methanogenic pathway. S5. Based on the methane production flux of the two types of methanogenic pathways, obtain the total methane production flux and the total methane isotope ratio. S6. Distribute the total methane produced to the plant-mediated transport pathway, the liquid-phase diffusion pathway, and the bubble escape pathway; S7. Analyze the oxidation processes of rhizosphere, soil-water interface, and bubble path, and calculate the residual methane isotope ratio after oxidation based on oxidative fractionation and isotope mass conservation. S8. Calculate the net methane emission flux and the corresponding methane isotope ratios for the three emission pathways. S9. Based on the net methane emission fluxes from the three emission pathways and the corresponding methane isotope ratios, perform flux-weighted mixing to obtain the total methane emission flux and the final emission endpoint. ; S10. Based on the contributions of the two types of methanogenic pathways, oxidation flux and oxidation ratio, the contributions of the three emission pathways, and the final emission end... To diagnose the process mechanisms of methane generation, oxidation, and emission pathways in paddy fields.

2. The method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics according to claim 1, characterized in that, Also includes: The isotope ratio R is used as a unified isotope calculation variable within the model for isotope fractionation, mass conservation, and flux-weighted mixing calculations during methane generation, oxidation, emission, and mixing processes.

3. The method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics according to claim 1, characterized in that, Step S3 also includes the following steps: Step S31: Calculate the available fresh carbon input entering the rhizosphere on the same day based on GPP; Step S32: Construct and dynamically update the rhizosphere active methanogenic carbon library; Step S33: Update the isotope ratios of the rhizosphere active methanogenic carbon library; GPP stands for Gross Primary Productivity of vegetation.

4. The method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics according to claim 1, characterized in that, Also includes: The allocation ratio of acetic acid cracking-type methanogenesis pathway and hydrogen nutrition-type methanogenesis pathway is determined by one or more factors among soil temperature, pH, moisture state, redox state, organic matter supply, rice growth stage, and field management practices.

5. The method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics according to claim 4, characterized in that, The acetic acid cracking-type methanogenesis pathway and the hydrogen nutrition-type methanogenesis pathway were respectively assigned methanogenic carbon isotope fractionation coefficients, and the methane production of the two methanogenesis pathways was calculated separately. The isotope ratios are then used to perform flux-weighted mixing based on the methane production fluxes of the two methanogenic pathways to obtain the total methane isotope composition.

6. The method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics according to claim 1, characterized in that, Apparent transport fractionation coefficients are set for the plant-mediated transport path, liquid-phase diffusion path, and bubble escape path, respectively, to calculate the methane isotope ratio at the emission end of the corresponding emission path.

7. The method for simulating the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics according to claim 1, characterized in that, The final emission end This is used to characterize the isotopic features of methane emission sources from paddy fields obtained from model simulations and compare them with observational constraint information to diagnose the contributions of methane generation pathways, oxidation intensity, and emission pathways. Among them, the observation constraint information is the regression intercept.

8. A simulation system for the source process mechanism of methane emission from paddy fields based on stable carbon isotope characteristics, characterized in that, Includes the following modules: (1) Data on photosynthetic carbon input, soil background carbon input, environmental and management factors, and carbon isotope input are obtained through the data input module; (2) Convert the carbon isotope input data into isotope values ​​using the isotope calculation module. The isotope ratio R is used as the isotope calculation variable within the model for isotope fractionation, mass conservation, and flux-weighted mixing calculations. (3) Construct a rhizosphere active methanogenic carbon library through the methane production module, and calculate the methane production flux and isotope ratio of the two types of methanogenic pathways: acetic acid cracking and hydrogen nutrition. (4) Calculate the rhizosphere oxidation, soil-water interface oxidation and optional bubble path oxidation processes through the methane oxidation module, and calculate the residual methane isotope ratio after oxidation based on isotope mass conservation. (5) Calculate the net emission flux and emission end isotope ratio of the three emission pathways, namely plant-mediated transport, liquid-phase diffusion and bubble escape, using the methane emission module; (6) Through the result mixing and mechanism diagnosis module, the net emission flux and isotope ratio of the three emission pathways are mixed by flux weighting, and the total methane emission flux and the final emission end are output. Diagnostic results regarding the mechanisms of methane generation, oxidation, and emission pathways; (7) Through the observation constraint and parameter calibration module, using methane flux, methane concentration, , , pore water, methane, oxygen One or more of the following observation information—water layer depth, Eh, or path separation—are used to calibrate, validate, and assess the uncertainty of model parameters and simulation results.

Images