Method for establishing soil organic carbon decomposition model based on microbial process

Abstract

The present invention provides a method for establishing a soil organic carbon decomposition model based on microbial processes, including: collecting soil and model parameters, defining the carbon pool in the dry and wet areas of the model and the physiological state and activity of microorganisms; calculating the speed of carbon pool conversion between dry and wet areas caused by changes in soil water content; calculating the speed of enzyme-catalyzed decomposition of POC to form DOC in the dry and wet areas, and the speed of active microorganisms absorbing DOC in the wet area; calculating the speed of microbial production of extracellular enzymes, growth, respiration and death, and the density of MAOC in the wet area at equilibrium; establishing a mass balance equation of enzyme carbon pool ENZ and soil particle organic carbon POC; establishing a mass balance equation of dissolved organic carbon DOC and mineral-bound organic carbon MAOC; and establishing a mass balance equation of microbial biomass MBC carbon pool in dry and wet areas. The present invention improves the model's ability to simulate the decomposition of organic carbon by soil microorganisms, especially the pulsed soil respiration changes caused by dry and wet changes.

Description

Technical Field

[0001] The present invention relates to the technical field of soil organic carbon content analysis, and in particular to a method for establishing a soil organic carbon decomposition model based on a microbial process. Background Art

[0002] Most of the existing soil organic carbon models based on microbial processes describe the decomposition of soil organic carbon as consisting of three processes: (1) the extracellular enzymes (ENZ) produced by microorganisms (MBC) catalyze the decomposition of soil aggregated particulate organic carbon (POC) into dissolved organic carbon (DOC); (2) microorganisms absorb DOC dissolved in the soil solution; (3) microorganisms assimilate the absorbed DOC and convert it into biomass and CO2 released by heterotrophic respiration. At the same time, the process of mineral adsorption of DOC into mineral-bound organic carbon (MAOC) and desorption of MAOC into DOC is described.

[0003] The density of soil carbon pool (particulate organic carbon POC, mineral-bound organic carbon MAOC, dissolved organic carbon DOC, microbial carbon MBC, extracellular enzyme ENZ) in the above models is defined as the content of carbon pool per unit volume of soil. Based on the density of carbon pool, most models use the Michaelis equation or the first-order reaction equation to calculate the reaction rate of carbon pool, such as the rate of soil enzyme catalytic decomposition of POC to produce DOC, the rate of microbial absorption and utilization of DOC, etc. These models do not consider the effect of water on the reaction rate of carbon pool from a mechanistic perspective, but use empirical formulas to describe the effect of water content on the reaction rate of soil carbon pool, resulting in obvious defects: it is impossible to simulate the pulsed soil respiration caused by soil dry-wet changes. In addition, they basically use the overall soil DOC density, rather than the soil solution DOC concentration, to calculate the soil mineral adsorption and desorption rate and the soil water flow transport DOC flux. Such a method will inevitably incorrectly calculate the MAOC density and water flow transport DOC flux.

[0004] We built a new model in 2022, based on soil moisture ( ) The overall soil is divided into dry and wet zones. In the wet zone, the surface of the soil matrix is ​​surrounded by a water film, while in the dry zone, the soil matrix is ​​exposed to the air in the soil pores. This model defines the soil carbon pool in the dry zone as the dry carbon pool, and the carbon pool in the wet zone as the wet carbon pool. Microorganisms are active in the wet zone, and dormant in the dry zone. This model is based on the carbon pool density in the dry and wet zones, and uses the Michaelis-Menten equation to calculate the reaction rate of the carbon pool in the dry and wet zones. The reaction rate of the overall soil is the sum of the product of the volume of each zone and its reaction rate. This method can describe the effect of soil moisture on the reaction rate of the carbon pool in the soil microenvironment to a certain extent, and thus can simulate the pulsed soil respiration changes caused by soil dry and wet changes, but it overestimates the soil respiration rate at the peak water content. Since this model does not take into account the MAOC carbon pool, nor the process of vertically transporting DOC by water flux, the application of the model is greatly limited. It is worth noting that mineral adsorption and desorption of DOC occur in soil solution, soil MAOC density changes with soil solution DOC concentration, and soil water transport is DOC in soil solution; however, the original model did not calculate soil solution DOC concentration, resulting in the model being unable to directly consider the addition of MAOC carbon pools and the calculation of DOC water transport process. For this reason, we invented a new method for establishing a soil organic carbon decomposition model based on microbial processes. Summary of the invention

[0005] The purpose of the present invention is to provide a method for establishing a soil organic carbon decomposition model that can describe the impact of soil microenvironment (temperature and water content, etc.) changes on the process of soil microbial decomposition of organic carbon and the changes in various carbon pools.

[0006] The purpose of the present invention can be achieved by the following technical measures: a method for establishing a soil organic carbon decomposition model based on a microbial process, the method for establishing a soil organic carbon decomposition model based on a microbial process comprising:

[0007] Step 1: Collect soil and model parameters, define the carbon pool in the dry and wet areas of the model and the physiological status and activity of microorganisms;

[0008] Step 2: Calculate the speed of carbon pool conversion between dry and wet areas caused by changes in soil water content per unit volume;

[0009] Step 3, calculate the rate of enzyme-catalyzed decomposition of POC to form DOC in the dry and wet areas, and the rate of DOC absorption by active microorganisms in the wet area;

[0010] Step 4, calculate the rates of microbial extracellular enzyme production, growth, respiration and death in dry and wet areas, as well as the MAOC density in the wet area of ​​the soil at equilibrium;

[0011] Step 5, establish the mass balance equation of enzyme carbon pool ENZ in dry and wet areas and soil particulate organic carbon POC in unit volume of soil;

[0012] Step 6, establish the mass balance equation of dissolved organic carbon DOC and mineral-bound organic carbon MAOC in dry and wet areas per unit volume of soil;

[0013] Step 7, establish the mass balance equation of the MBC carbon pool of microbial biomass in dry and wet areas per unit volume of soil.

[0014] The purpose of the present invention can also be achieved by the following technical measures:

[0015] In step 1, the carbon pools in the dry and wet areas of the model are defined according to the soil volumetric water content. The total soil organic carbon includes the following five carbon pools: particulate organic carbon POC, mineral-bound organic carbon MAOC, dissolved organic carbon DOC, microbial carbon MBC, and extracellular enzymes ENZ; , , and They are the total density of the four carbon pools per unit volume of soil; since soil organic carbon exists in soil pores, the soil pores are defined as The volume space occupied by the water is the wet area, and its size is the volumetric water content ; The space occupied by air is the dry area, and its size is ; The soil carbon pool in the dry area is called the dry area carbon pool, and the soil carbon pool in the wet area is called the wet area carbon pool; the four different types of carbon pools, DOC, MAOC, MBC, and ENZ, are divided into dry and wet carbon pools respectively; the wet carbon pool , , and They are the density of the four carbon pools per unit volume in the wet area, the dry carbon pool , , and are the densities of the four carbon pools per unit volume in the dry area; therefore, the overall density of the soil carbon pool per unit volume is the sum of the product of the carbon pool density in the dry and wet areas of the pore microenvironment and the volume of each area. For the DOC carbon pool, it can be written as:

[0016] (1)

[0017] The above form is also applicable to MAOC, ENZ and MBC carbon pools;

[0018] The overall density of POC carbon pool per unit volume of soil The density of particulate organic carbon in soil pores The relationship is as follows:

[0019] (2).

[0020] In step 1, the activity or potential activity and dormancy of microorganisms and their physiological activities are defined according to the dry and wet areas. Since the activity of microorganisms is inseparable from the soil solution, the microorganisms in the wet area are defined as active or potentially active, and in the dry area as dormant. Only the active microorganisms in the wet area can absorb and utilize the DOC in the wet area solution of the soil through DOC diffusion and produce extracellular enzymes. Potentially active microorganisms cannot absorb DOC and do not produce extracellular enzymes. Dormant microorganisms in the dry area cannot absorb DOC, do not produce enzymes, and do not die.

[0021] In step 2, when the water content increases, part of the dry area becomes a wet area, and this part of the dry carbon pool becomes part of the wet carbon pool; and for the microbial carbon pool, some dormant microorganisms in the dry area enter an active or potentially active state; when the water content decreases, part of the wet area becomes a dry area, and this part of the wet carbon pool becomes part of the dry carbon pool; and for the microbial carbon pool, some active or potentially active microorganisms in the wet area enter a dormant state; when the water content increases or decreases, the speed of conversion between the dry and wet areas of the four carbon pools in a unit volume of soil , , and is the product of the volumetric water content change rate and the carbon pool density in the dry or wet area; for the DOC carbon pool, It can be expressed as:

[0022] (3)

[0023] The above formula is also applicable to MAOC, ENZ and MBC carbon pools.

[0024] In step 3, the Michaelis-Menten kinetic equation is used to calculate the rate of enzyme-catalyzed decomposition of POC to form DOC in the dry and wet areas and the rate of DOC absorption by active microorganisms in the wet area, and the Arrhenius equation is used to calculate the effect of temperature on the decomposition rate and absorption rate;

[0025] The rate at which POC per unit volume of soil is decomposed into DOC by enzymes , which is determined by the volume of the dry / wet area in the soil pores and the POC catalytic decomposition rate in the dry and wet areas. and Decision:

[0026] (4)

[0027] and is determined by the POC concentration and described by the Michaelis-Menten kinetic equation, which is proportional to the concentration of each enzyme:

[0028] (5)

[0029] (6)

[0030] in It is the maximum rate at which POC is enzymatically degraded to form DOC at a unit concentration when the substrate concentration does not limit the reaction rate. is the half-saturation constant of the Michaelis-Menten kinetic equation, that is, the substrate concentration when the reaction rate is half of the maximum reaction rate; is the catalytic efficiency of the enzyme in the dry area. Compared with the wet area, the catalytic efficiency is reduced due to the fixation of the enzyme in the dry area. The Arrhenius equation is used to calculate the temperature Impact on it:

[0031] (7)

[0032] in At the reference temperature The maximum rate of enzymatic decomposition and polymerization of POC per unit concentration, is the activation energy required for depolymerization of POC, is the universal gas constant;

[0033] Wetland DOC is the DOC dissolved in the soil solution, so the wetland DOC density is expressed as the solution DOC concentration; the rate at which active microorganisms in the wetland absorb and assimilate DOC per unit volume It is determined by the soil solution DOC and pore air O2 concentration and is described by the Michaelis-Menten kinetic equation; It is also proportional to the density of active microbial biomass and is calculated as follows:

[0034] (9)

[0035] in It is the maximum rate of DOC absorption by microorganisms per unit concentration when the concentration of DOC and O2 does not limit the absorption rate. is the carbon pool density of active microorganisms per unit volume of wetland area, is the O2 concentration in soil air; and are the half-saturation constants of the Michaelis-Menten equation for DOC and O2 concentrations, respectively;

[0036] Using the Arrhenius equation to calculate temperature right Impact:

[0037] (10)

[0038] in At the reference temperature The maximum rate at which microorganisms absorb DOC at a unit concentration; It is the activation energy required for microorganisms to absorb DOC.

[0039] In step 4, the production of extracellular enzymes and the required respiration, maintenance respiration, growth and growth respiration, and death rates of microorganisms in the wet zone of the soil are calculated, and the maintenance respiration rate of dormant microorganisms in the dry zone is calculated;

[0040] The rate of extracellular enzyme production by active microorganisms in wet soil areas It is proportional to the speed at which active microorganisms absorb and assimilate DOC and can be calculated as:

[0041] (12)

[0042] in, The constant percentage of enzyme produced to DOC assimilated by active microorganisms; the respiration rate required to produce extracellular enzymes The calculation is as follows:

[0043] (15)

[0044] in is the efficiency of carbon utilization by microorganisms;

[0045] The DOC absorbed and assimilated by active microorganisms in the wet soil area is used to produce extracellular enzymes and the remaining part after respiration is required. The maintenance respiration rate of active microorganisms and its MBC density The Arrhenius equation is used to describe the temperature effect, which is calculated as follows:

[0046] (16)

[0047] in, is the maintenance respiration rate per unit microbial mass at the reference temperature, It is the activation energy required by microorganisms to maintain physiological activities;

[0048] If the remainder of the above After meeting the requirement of maintaining respiration, it can also be used for the growth of microorganisms and the required growth respiration. , the growth rate of active microorganisms in wet areas The calculation is as follows:

[0049] (17)

[0050] The required respiration rate for growth The calculation is as follows:

[0051] (18)

[0052] If the remainder of the above It can only be used to maintain more than half of the respiration, but not all of it. At this time, the active microorganisms are in a state of starvation and need to consume their own biomass to meet all of the respiration. If the remaining part cannot meet half of the respiration, the active microorganisms in the starvation state begin to enter a potential activity state. At this time, the microorganisms stop absorbing DOC and stop producing extracellular enzymes. The respiration is two orders of magnitude lower than that in the active state, and the death rate is one order of magnitude lower than that in the active state. and are the biomass carbon density when the wet zone microorganisms are active and potentially active, respectively, and can be expressed as

[0053] (19)

[0054] Maintenance respiration rate of potentially active microorganisms in wet areas The calculation is as follows:

[0055] (20)

[0056] Among them, the reduction factor , b indicates that the maintenance respiration rate of potentially active microorganisms is only one percent of that in the active state;

[0057] Use the first-order kinetic equation to describe the death rate of microorganisms in the unit volume of wet area when they are active and potentially active :

[0058] (twenty one)

[0059] in is the death rate constant of active microorganisms, It is a factor that reduces the rate of death of potentially active microorganisms;

[0060] Maintenance respiration rate of dormant microorganisms in dry zone microenvironment , is one percent of the active state and is calculated as follows:

[0061] (twenty two).

[0062] In step 4, calculate the rate of CO2 release by heterotrophic respiration of microorganisms per unit volume of soil. ; Respiration is maintained by active or potentially active microorganisms in wet areas or , respiration required for the production of extracellular enzymes by active microorganisms and growth breathing and the maintenance of respiration of dormant microorganisms composition:

[0063] (twenty three).

[0064] In step 4, the MAOC density in the soil wet zone at equilibrium is calculated using the Langmuir adsorption function based on the DOC concentration in the soil solution;

[0065] When the solid-liquid two-phase adsorption and desorption reaches equilibrium, the Langmuir adsorption function is used to describe the MAOC density per unit volume of wet area. The relationship with the change of soil solution DOC concentration is:

[0066] (twenty four)

[0067] in is the soil bulk density, is the binding affinity parameter, It is the maximum amount of DOC adsorbed by minerals per unit volume of soil.

[0068] In step 5, the enzymes in the wet zone of soil are produced by active microorganisms, which are reduced due to inactivation. At the same time, the enzyme carbon pool between dry and wet zones changes due to changes in water content. The mass balance equation of the enzyme per unit volume in the wet zone of soil is established:

[0069] (25)

[0070] in, is the turnover constant of enzyme inactivation in the wet zone. The enzyme inactivation is described by the first-order kinetic equation. The inactivated enzyme enters the DOC pool in the wet zone.

[0071] The enzymes in the dry area are reduced due to inactivation. At the same time, the conversion of enzyme carbon pools between dry and wet areas is changed due to changes in water content. Compared with the enzymes in the wet area, the dry area has no water, which leads to a decrease in the inactivation rate of the enzymes. Therefore, the mass balance equation of the enzymes in the dry area per unit volume of soil is established:

[0072] (26)

[0073] in, is the reduction factor of the enzyme inactivation rate in the dry zone.

[0074] In step 5, particulate organic carbon (POC) mainly comes from plant litter and a part of dead microorganisms, and decreases as it is decomposed into DOC by enzymes. Thus, the POC mass balance equation per unit volume of soil is established:

[0075] (27)

[0076] in, It is the part of dead microorganisms converted into POC. is the input item of vegetation litter entering the soil carbon pool per unit time, It is the portion of vegetation litter input into POC.

[0077] In step 6, the DOC in the wet zone solution mainly comes from the catalytic decomposition of POC, the inactivation of enzymes, part of dead microorganisms and plant litter, and plant root secretions. It decreases as active microorganisms absorb DOC and is affected by the transition between dry and wet zone DOC, the adsorption-desorption process, and the vertical transport of DOC by soil water. Therefore, the mass balance equation of DOC in the wet zone solution per unit volume of soil is:

[0078] (29)

[0079] in, It is the input rate of DOC contained in plant root exudates per unit volume of soil. Since the input of exudates into the soil requires soil water, it is assumed that all of them enter the wet zone. It is the sum of the amount of DOC adsorbed on the mineral surface in the unit volume of soil per unit time (-) and the amount of DOC desorbed by MAOC into the solution (+); is the vertical transport flux of DOC by soil water;

[0080] The DOC in the dry area comes from the catalytic decomposition of POC, the inactivation of enzymes in the dry area, and part of the litter, and is affected by the transformation of DOC between the dry and wet areas; therefore, the mass balance equation of DOC in the dry area per unit volume of soil is:

[0081] (30) .

[0082] In step 6, the wet zone MAOC density is mainly affected by the adsorption-desorption process of DOC and the MAOC transition between dry and wet zones; thus, the soil wet zone MAOC mass balance equation per unit volume of soil is established:

[0083] (31)

[0084] The MAOC density in the dry area is affected by the transformation of MAOC between the dry and wet areas. The mass balance equation of MAOC in the dry area per unit volume of soil is as follows:

[0085] (32).

[0086] In step 7, when the DOC absorbed by the active microorganisms in the wet zone can be used for growth, their biomass will decrease due to death. At the same time, the conversion of biomass between dry and wet zones will change due to the change in water content. Therefore, the mass balance equation of MBC of active microorganisms in the wet zone per unit soil can be written as:

[0087] (33)

[0088] The mass balance equation of active microorganisms in the hungry state in the wet area of ​​unit volume of soil can be written as:

[0089] (34)

[0090] The potentially active microorganisms in the wet zone not only consume their own biomass to maintain respiration, but also reduce their biomass through death. At the same time, the conversion of biomass between dry and wet zones changes due to changes in water content. The mass balance equation of the potentially active microorganisms MBC in the wet zone per unit volume of soil is:

[0091] (35)

[0092] The dormant microorganisms in the dry zone are in a very low state of maintaining respiration, which requires consumption of their own biomass. At the same time, the conversion of biomass between dry and wet zones is changed due to changes in water content. The mass balance equation of dormant microorganisms in the dry zone per unit volume of soil is:

[0093] (36).

[0094] The method for establishing a soil organic carbon decomposition model based on microbial processes in the present invention takes into account the differences between different microenvironments of solution and air in soil pores, and distinguishes the carbon pool density and chemical reaction rate of different microenvironmental reaction points. Thus, the carbon pool density in the aqueous solution and air in the soil pores is defined respectively, wherein the space occupied by the aqueous solution is the wet area, and the space occupied by the air is the dry area; the four carbon pools, namely MAOC, DOC, MBC, and ENZ, are each divided into two dry and wet carbon pools, and then the volume weight is used to calculate the overall density of different carbon pools per unit volume of soil. When the water content changes, the volume of the dry and wet areas in the soil pores changes, resulting in a transition between the dry and wet carbon pools. The Arrhenius equation is used to calculate the effect of temperature on the reaction rate of the carbon pool; depending on the density of the dry / wet area carbon pool, the Michaelis-Menten equation is used to calculate the reaction rate of the dry / wet area carbon pool, and then the volume weight is used to calculate the reaction rate per unit volume of soil. The changes in DOC and MAOC concentrations in the wet zone due to changes in the adsorption and desorption processes of DOC by soil minerals are considered, and the Langmuir adsorption function is used to describe the relationship between the DOC concentration and the MAOC density in the soil wet zone solution at equilibrium; and the influence of the process of vertical DOC transport by soil water flow on the DOC concentration is considered in the wet zone DOC mass balance equation.

[0095] The model established by the present invention describes the influence of soil water on the decomposition and transport of organic carbon and the physiological state of microorganisms from a mechanistic perspective, describes the influence of the adsorption and desorption of DOC by soil minerals on DOC concentration, and describes an important stabilization mechanism for the sequestration of organic carbon in the soil: DOC transported downward by soil water flows forms relatively stable MAOC in the deep soil layer and is not decomposed by microorganisms. These descriptions improve the model's ability to simulate the decomposition of organic carbon by soil microorganisms, especially the ability to simulate the pulsed soil respiration changes caused by dry-wet changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 It is a flow chart of a specific embodiment of the method for establishing a soil organic carbon decomposition model based on microbial processes of the present invention;

[0097] Figure 2 This is a schematic diagram of the soil organic carbon decomposition model based on microbial processes;

[0098] Figure 3 This is the coupling structure diagram of the vertically layered soil organic carbon decomposition model and the Noah-MP land surface model;

[0099] Figure 4 Schematic diagram of the observed half-hourly air temperature and precipitation, and the observed and simulated volumetric water content and temperature of the soil at 5 cm and 10 cm depth;

[0100] Figure 5Schematic diagram for observing and simulating the CO2 flux on the soil surface and the CO2 concentration at 2cm and 10cm depth every half hour;

[0101] Figure 6 Schematic diagram of the simulated changes in the density of DOC, MBC, MAOC, ENZ and POC in the 13 cm soil layer every half hour;

[0102] Figure 7 Schematic diagram of the vertical distribution of MAOC at a depth of 0-60 cm in late 2007 with and without considering the vertical transport of DOC by soil water flow. DETAILED DESCRIPTION

[0103] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0104] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0105] The definitions of the variables and parameters used in the model are shown in Table 1.

[0106] Table 1. Definition of model variables and parameters

[0107] like Figure 1 , which is a flow chart of a method for establishing a soil organic carbon decomposition model based on a microbial process of the present invention. The method for establishing a soil organic carbon decomposition model based on a microbial process comprises:

[0108] Step 1, collect soil and model parameters;

[0109] Collection of soil parameters, including soil bulk density (kg m -3 ), porosity (m 3 m -3 ), soil binding affinity parameters (m 3 g -1), maximum soil MAOC per unit mass (g C kg -1 The parameters required for the collection model are shown in Table 2.

[0110] Table 2. Values ​​of model parameters

[0111]

[0112] Step 2, define the carbon pool in the dry and wet areas of the model according to the soil volumetric water content; define the microbial activity or potential activity and dormancy state and its physiological activity according to the dry and wet areas;

[0113] like Figure 2 As shown in the figure, soil total organic carbon includes the following five carbon pools: particulate organic carbon (POC), mineral bound organic carbon (MAOC), dissolved organic carbon (DOC), microbial carbon (MBC), and extracellular enzymes (ENZ). , , and They are the total density of the four carbon pools per unit volume of soil (g C m -3 Since soil organic carbon exists in soil pores, we define soil pores ( ) is the space occupied by water in the wet area, and its size is the volumetric water content. ; The space occupied by air is the dry area, and its size is The soil carbon pool in the dry area is called the dry area carbon pool, and the soil carbon pool in the wet area is called the wet area carbon pool. Figure 2 As shown in the figure, the four different types of carbon pools, DOC, MAOC, MBC, and ENZ, are divided into two carbon pools, dry and wet. , , and They are the densities of the four carbon pools per unit volume of wet area (g C m -3 ), dry carbon pool , , and They are the densities of the four carbon pools per unit volume of dry area (g C m -3 ). Therefore, the overall density of the soil carbon pool per unit volume is the sum of the carbon pool density of each dry and wet zone in the pore microenvironment multiplied by the volume of each zone. For example, the DOC carbon pool can be written as:

[0114] (1)

[0115] The above formula (1) is also applicable to MAOC, ENZ and MBC carbon pools.

[0116] Since the magnitude of POC is more than two orders of magnitude greater than its decomposition rate, the effect of decomposition on POC content can be ignored on the time scale of changes in water content. Therefore, the difference in POC between dry and wet areas is not considered, but the different decomposition rates of POC in dry and wet areas are calculated. The overall density of POC carbon pool per unit volume of soil (g C m -3 ) and the density of particulate organic carbon in soil pores (g C m -3 ) is as follows:

[0117] (2)

[0118] Since the activity of microorganisms cannot be separated from the soil solution, it is defined that microorganisms in the wet area are active or potentially active, and in the dry area they are dormant. Only active microorganisms in the wet area can absorb and utilize DOC in the wet area solution of the soil through solution DOC diffusion, and can produce extracellular enzymes, while potentially active microorganisms cannot absorb DOC and do not produce extracellular enzymes. Dormant microorganisms in the dry area cannot absorb DOC, do not produce enzymes, and do not die.

[0119] Step 3: Calculate the rate of conversion of carbon pools (DOC, MAOC, MBC and ENZ) between dry and wet zones due to changes in soil water content per unit volume.

[0120] like Figure 2 As shown in the figure, when the volumetric water content changes, a conversion occurs between the dry and wet carbon pools (double arrows). When the water content increases, part of the dry area becomes a wet area, and this part of the dry carbon pool becomes part of the wet carbon pool. For the microbial carbon pool, some dormant microorganisms in the dry area will be activated and enter an active or potentially active state. When the water content decreases, part of the wet area becomes a dry area, and this part of the wet carbon pool becomes part of the dry carbon pool. For the microbial carbon pool, some active or potentially active microorganisms in the wet area enter a dormant state. , , and They represent the conversion rate between the dry and wet areas of the four carbon pools per unit volume of soil when the water content changes (g C m –3 s –1 ). For example, for the DOC carbon pool, It can be expressed as:

[0121] (3)

[0122] The above formula (3) is also applicable to MAOC, ENZ and MBC carbon pools.

[0123] Step 4, using the Michaelis-Menten kinetic equation to calculate the rate of enzyme-catalyzed decomposition of POC to form DOC in the dry and wet zones, and using the Arrhenius equation to calculate the effect of temperature on the decomposition rate;

[0124] like Figure 2 As shown in the figure, enzymes in both the dry and wet areas can depolymerize POC to produce DOC. In the wet area, the enzymes produced by microorganisms diffuse to the surface of POC through soil moisture and can catalyze the depolymerization of POC to produce DOC; in the dry area, the enzymes that are active and attached to the surface of POC can still catalyze the depolymerization of POC to produce DOC, but due to the fixation of the enzymes in the dry area (no diffusion), their catalytic efficiency is reduced compared to that in the wet area. The rate at which POC per unit volume of soil is decomposed into DOC by enzymes (g C m –3 s –1 ), which is determined by the dry / wet area volume in the soil pores and the respective POC catalytic depolymerization rate ( and (g C m –3 s –1 )) Decision:

[0125] (4)

[0126] POC catalytic depolymerization rate per unit volume of dry and wet areas and Determined by the POC concentration, described by the Michaelis-Menten kinetic equation, they are also proportional to the size of the respective enzyme concentrations:

[0127] (5)

[0128] (6)

[0129] in It is the maximum rate of POC to form DOC by enzymatic polymerization per unit concentration when the substrate concentration does not limit the reaction rate (g C m -3 (g C m -3 ) -1 s -1 ), is the half-saturation constant of the Michaelis-Menten kinetic equation (gC m -3 ), that is, the substrate concentration at which the reaction rate is half of the maximum reaction rate; is the catalytic efficiency of the enzyme in the dry zone. The Arrhenius equation is used to calculate the temperature (K) Yes Impact:

[0130] (7)

[0131] in At the reference temperature The maximum rate of enzymatic decomposition and polymerization of POC per unit concentration (g C m -3 (g Cm -3 ) -1 s -1 ), is the activation energy required for depolymerization of POC (J mol –1 ), is the universal gas constant (=8.31 ​​J mol –1 K –1 ). is a linear function of temperature with a slope of and the intercept is , calculated as follows:

[0132] (8)

[0133] Step 5, using the Michaelis-Menten kinetic equation to calculate the rate at which active microorganisms in the wet area absorb DOC, and using the Arrhenius equation to calculate the effect of temperature on the absorption rate;

[0134] The wet area DOC is the DOC dissolved in the soil solution, so the wet area DOC density is expressed as the solution DOC concentration. Figure 2 As shown in Figure 2, wetland active microorganisms need to absorb and assimilate DOC in the solution to survive. The rate at which wetland active microorganisms absorb and assimilate DOC per unit volume (g C m -3 s -1 ) is determined by the soil solution DOC and pore air O2 concentrations and is described by the Michaelis-Menten kinetic equation; It is also proportional to the density of active microbial biomass and is calculated as follows:

[0135] (9)

[0136] in It is the maximum rate of DOC absorption by microorganisms per unit concentration when the concentration of DOC and O2 does not limit the absorption rate (g C m -3 (g C m -3 ) -1 s -1 ), is the carbon pool density of active microorganisms per unit volume of wetland area (gC m -3 ), is the O2 concentration in soil air (m3 O2m –3 air); (g C m –3 soil) and (m 3 O2m –3 air) are the Michaelis-Menten half-saturation constants for DOC and O2 concentrations, respectively.

[0137] Using the Arrhenius equation to calculate temperature right Impact:

[0138] (10)

[0139] in At the reference temperature The maximum rate of DOC absorption by microorganisms per unit concentration (g C m -3 (g C m -3 ) -1 s -1 ); is the activation energy required for microbial uptake of DOC (J mol –1 ).

[0140] Assumptions is a linear function of temperature:

[0141] (11)

[0142] in and are the slope and intercept respectively. is a constant.

[0143] Step 6, calculate the rates of extracellular enzyme production, respiration, growth and death of microorganisms in dry and wet areas, and calculate the rate of CO2 release by heterotrophic respiration of microorganisms per unit volume of soil;

[0144] like Figure 2 As shown, active microorganisms in wet soil areas can produce extracellular enzymes, die, have respiration required for enzyme production, maintain respiration, and when there is growth, there is growth respiration; but potentially active microorganisms only have lower-level maintenance respiration and death; and dormant microorganisms only have maintenance respiration. Active microorganisms in wet soil areas absorb and assimilate DOC, which is first used to produce extracellular enzymes and the required respiration. The speed of active microorganisms producing extracellular enzymes in wet soil areas (g C m -3 s -1 ) is proportional to the rate at which active microorganisms absorb and assimilate DOC and can be calculated as:

[0145] (12)

[0146] in, The enzyme produced is a constant percentage of DOC assimilated by the active microorganisms.

[0147] The rate at which exoenzymes are produced by active microorganisms The respiratory rate required for the production of extracellular enzymes (g Cm -3 s -1 ) must satisfy the production efficiency of the extracellular enzyme , It is also the efficiency of carbon utilization by microorganisms, namely:

[0148] (13)

[0149] Studies have shown that It decreases with increasing temperature and is usually described as a linear function of temperature with a slope of and the intercept is , The calculation is as follows:

[0150] (14)

[0151] From the above formula (13), we can calculate , calculated as follows:

[0152] (15)

[0153] The remaining DOC absorbed and assimilated by active microorganisms in the wet zone of the soil, after being used to produce extracellular enzymes and the required respiration, must first be used to maintain respiration, that is, the respiration required by active microorganisms in the wet zone microenvironment to maintain basic physiological activities. (g C m -3 s -1 ) and its MBC density The Arrhenius equation is used to describe the temperature effect, which is calculated as follows:

[0154] (16)

[0155] in, is the maintenance respiration rate per unit microbial mass at the reference temperature (g C m -3 (g C m -3 ) -1 s -1 ), is the activation energy required for microorganisms to maintain physiological activities (J mol –1 ).

[0156] If the remainder of the above After meeting the requirement of maintaining respiration, it can also be used for the growth of microorganisms and the required growth respiration. Then according to the microbial carbon utilization efficiency , the growth rate of active microorganisms in wet areas (g Cm -3 s -1 ) is calculated as follows:

[0157] (17)

[0158] The required respiration rate for growth (g C m -3 s -1 ) is calculated as follows:

[0159] (18)

[0160] If the remainder of the above It can only be used to maintain more than half of the respiration, but cannot meet all of it. At this time, the active microorganisms are in a state of starvation and need to consume their own biomass to meet all of the maintenance of respiration. When the external environment that is not conducive to wet zone microorganisms deteriorates, if the above remaining part cannot meet half of the maintenance of respiration, the active microorganisms in the starvation state begin to enter a potential active state. At this time, the microorganisms stop absorbing DOC and stop producing extracellular enzymes. The maintenance of respiration is two orders of magnitude lower than that of the active state, and the death rate is one order of magnitude lower than that of the active state. If there is substrate input or the environment improves, the potentially active microorganisms will enter the active state in a short time (minutes to hours). and The biomass carbon density of wetland microorganisms in active and potential active states (g C m -3 ), which can be expressed as

[0161] (19)

[0162] Maintenance respiration rate of potentially active microorganisms in wet areas (g C m -3 s -1 ) is calculated as follows:

[0163] (20)

[0164] Among them, the reduction factor , b indicates that the maintenance respiration rate of potentially active microorganisms is only one percent of that in the active state;

[0165] Use the first-order kinetic equation to describe the death rate of microorganisms in the unit volume of wet area when they are active and potentially active (g C m -3 s -1 ):

[0166] (twenty one)

[0167] in is the death rate constant of active microorganisms, It is a factor that reduces the rate of death of potentially active microorganisms;

[0168] Maintenance respiration rate of dormant microorganisms in dry zone microenvironment (g C m -3 s -1 ), is one percent of the active state and is calculated as follows:

[0169] (twenty two)

[0170] Heterotrophic respiration rate of soil microorganisms per unit volume (g C m -3 s -1 ) Respiration is maintained by active or potentially active microorganisms in wet areas ( or ), respiration required for the production of extracellular enzymes by active microorganisms and growth breathing and the maintenance of respiration of dormant microorganisms composition:

[0171] (twenty three)

[0172] Step 7, according to the DOC concentration of the soil solution, the Langmuir adsorption function is used to calculate the MAOC density in the soil wet area at equilibrium;

[0173] The mineral surface in the wet area of ​​the soil adsorbs DOC from the soil solution to form MAOC, and the adsorbed DOC will also desorb into the soil solution. When in equilibrium, the adsorption and desorption rates are equal. When the DOC concentration in the wet area solution changes, the adsorption and desorption rates will undergo significant nonlinear changes, resulting in an imbalance in speed, and in a very short time scale (seconds to minutes), it is much faster than the absorption rate of DOC by microorganisms, and the equilibrium state is quickly reached.

[0174] When the solid-liquid two-phase adsorption and desorption reaches equilibrium, the Langmuir adsorption function is used to describe the MAOC density per unit volume of wet area. (g C m -3 ) and soil solution DOC concentration The change relationship is:

[0175] (twenty four)

[0176] in is the soil bulk density (kg m -3 ), is the binding affinity parameter, which represents the interaction strength between minerals and DOC per unit mass of soil (m 3 g -1 ); is the maximum amount of DOC adsorbed by minerals per unit volume of soil (g Ckg -1 soil).

[0177] Step 8, establishing the mass balance equation of enzyme carbon pool ENZ in dry and wet zones per unit volume of soil;

[0178] like Figure 2 As shown in the figure, the enzymes in the wet zone of soil are produced by active microorganisms, which are reduced due to inactivation. At the same time, the enzyme carbon pool between dry and wet zones changes due to changes in water content. The mass balance equation of enzymes per unit volume in the wet zone of soil is:

[0179] (25)

[0180] in, is the turnover constant of enzyme inactivation in the wet zone. The enzyme inactivation is described by the first-order kinetic equation. The inactivated enzyme enters the DOC pool in the wet zone.

[0181] like Figure 2 As shown in the figure, the enzyme in the dry area is reduced due to inactivation, and at the same time, the conversion of enzyme carbon pool between dry and wet areas is changed due to changes in water content. Compared with the enzyme in the wet area, the dry area has no water, which leads to a decrease in the inactivation rate of the enzyme. The mass balance equation of the enzyme in the dry area per unit volume of soil is:

[0182] (26)

[0183] in, is the reduction factor of the enzyme inactivation rate in the dry zone.

[0184] Step 9, establishing a mass balance equation for soil particulate organic carbon (POC) per unit volume;

[0185] like Figure 2 As shown, particulate organic carbon (POC) mainly comes from plant litter and part of dead microorganisms, and decreases as it is decomposed into DOC by enzymes. The mass balance equation of POC per unit volume of soil is:

[0186] (27)

[0187] The second term on the right side of the equation is the input term for the conversion of dead microorganisms into POC. It is the part of dead microorganisms converted into POC. is the input of vegetation litter into the soil carbon pool per unit time (g C m -3 s -1 ), It is the portion of vegetation litter input into POC.

[0188] Step 10, calculate the vertical transport flux of water flow to DOC, consider the effect of mineral adsorption-desorption process on DOC density in wet area, and establish the mass balance equation of dissolved organic carbon DOC in dry and wet areas;

[0189] The vertical transport flux of DOC by water flow in the solution is one order of magnitude larger than the hydrodynamic diffusion DOC flux. In the model, only the vertical transport flux of DOC by water flow is considered. The effect on DOC concentration, The calculation is as follows:

[0190] (28)

[0191] in is the soil water vertical flux (ms -1 ).

[0192] like Figure 2 As shown, the DOC in the wet zone solution mainly comes from the catalytic decomposition of POC, the inactivation of enzymes, part of dead microorganisms and plant litter, and plant root secretions. It decreases as active microorganisms absorb DOC, and is affected by the transition between dry and wet zone DOC and the adsorption-desorption process. In vertically layered soils, the DOC in the wet zone solution must also be affected by the vertical transport of DOC in soil water. The mass balance equation of the DOC in the wet zone solution per unit volume of soil is:

[0193] (29)

[0194] in, is the input rate of DOC contained in plant root exudates per unit volume of soil (g C m -3 s -1 ), since the input of secretions into the soil requires soil water, it is considered that they all enter the wet zone; It is the sum of the amount of DOC adsorbed on the mineral surface in the wet zone solution (-) and the amount of MAOC desorbed into the solution (+) per unit time (g C m -3 s -1 The rightmost term of the equation is the gradient change of vertical transport of DOC by soil water.

[0195] like Figure 2 As shown in the figure, the DOC in the dry area only comes from the catalytic decomposition of POC, the inactivation of enzymes in the dry area, and part of the litter, and is affected by the DOC conversion between the dry and wet areas. The mass balance equation of DOC in the dry area per unit volume of soil is:

[0196] (30)

[0197] Because DOC in the dry zone cannot be absorbed and utilized by dormant microorganisms, the DOC generated by the catalytic decomposition of POC in the dry zone will continue to accumulate.

[0198] Step 11: Establish the mass balance equation of mineral-bound organic carbon (MAOC) in dry and wet areas.

[0199] like Figure 2 As shown in Figure 2, the density of MAOC in the wet zone is mainly affected by the adsorption-desorption process of DOC in the minerals in the soil solution and the transformation of MAOC between the dry and wet zones. The mass balance equation of MAOC in the wet zone of soil per unit volume of soil is:

[0200] (31)

[0201] Since there is no soil solution, there is no adsorption and desorption process of minerals in the dry zone, and the change of MAOC density in the dry zone comes from the conversion between dry and wet zones. The mass balance equation of MAOC in the dry zone of soil per unit volume of soil is as follows:

[0202] (32)

[0203] Step 12, establish the mass balance equation of the MBC carbon pool of microbial biomass in dry and wet areas per unit volume of soil.

[0204] When the DOC absorbed by the active microorganisms in the wet zone can be used for growth, their biomass will decrease due to death, and at the same time, the conversion of biomass between dry and wet zones will change due to changes in water content. The mass balance equation of the MBC of active microorganisms in the wet zone per unit soil can be written as:

[0205] (33)

[0206] When the active microorganisms in the wet zone are in a state of starvation, not only do they need to consume their own biomass to maintain respiration, but they also decrease due to death. At the same time, the conversion of biomass between dry and wet zones is changed due to changes in water content. The MBC mass balance equation for active microorganisms in a state of starvation in the wet zone per unit volume of soil can be written as:

[0207] (34)

[0208] The potentially active microorganisms in the wet zone not only consume their own biomass to maintain respiration, but also reduce their biomass through death. At the same time, the conversion of biomass between dry and wet zones changes due to changes in water content. The mass balance equation of the potentially active microorganisms MBC in the wet zone per unit volume of soil is:

[0209] (35).

[0210] The dormant microorganisms in the dry zone are in a very low state of maintaining respiration, which requires consumption of their own biomass. At the same time, the conversion of biomass between dry and wet zones is changed due to changes in water content. The mass balance equation of dormant microorganisms in the pore dry zone per unit volume of soil is:

[0211] (36).

[0212] In a specific embodiment of the present invention, the model established in the invention is applied to the Santa Rita grassland site in the semi-arid area of ​​Arizona in the southwestern United States to simulate the density of various carbon pools of soil organic carbon and the heterotrophic respiration rate of microorganisms decomposing organic carbon and releasing CO2. This embodiment provides a specific implementation process of the model application (the model establishment method does not involve a specific model algorithm, and the present invention does not introduce a specific algorithm).

[0213] Step 21, in order to obtain the input of the soil organic carbon decomposition model based on microbial processes, the model is coupled to the Noah-MP land surface process model. The Noah-MP model runs with a time step of half an hour (1800 seconds).

[0214] According to the vertical layered structure of the soil water and heat transfer model of the Noah-MP land surface model (the soil at a depth of 2m is divided into 16 layers, the surface layer is 2cm thick, and the deeper the soil layer, the thicker the soil layer), the soil organic carbon in the vertical profile of the soil is layered. In this way, the input variables such as the soil moisture content, temperature, O2 concentration, vegetation litter rate and root secretion rate of each layer calculated by the land surface model, as well as the vertical water flow between layers can be used to drive the soil organic carbon decomposition model. Then, the vertical transport flux of DOC by water flow between soil layers, the size of each carbon pool in each soil layer, and the CO2 release rate of heterotrophic respiration of microorganisms can be calculated. In this way, the Noah-MP model (referred to as the coupled model) for coupled soil organic carbon decomposition can calculate the CO2 concentration of each soil layer and the surface CO2 flux based on the calculated autotrophic respiration of vegetation roots and the heterotrophic respiration rate of microorganisms. Figure 3 As shown, the thick solid box contains the vertically layered soil organic carbon decomposition model, and the hollow arrows between soil layers in the thick solid box represent the transport process of DOC by soil water flow; the outer part of the thick solid box is the input variable provided by the Noah-MP land surface model (the arrow direction is toward the thick solid box), and the hollow arrows outside the thick solid box represent the vertical transmission process of O2 and CO2 in soil air.

[0215] Step 22, collect meteorological data such as atmospheric wind speed, temperature, humidity, pressure, precipitation, solar shortwave radiation and downward longwave radiation flux observed every half hour at the Santa Rita meadow site in 2007, Figure 4 a shows the temperature and precipitation data. Observations of temperature and volumetric water content at different soil depths (5, 10, 20, 30, 50, 70, 100 and 130 cm) were collected in 2007. Figure 4 The blue dashed lines in be show the observed temperature and volumetric water content at 5 and 10 cm. The observed values ​​of soil temperature and volumetric water content in early January are used to obtain the estimated values ​​of soil temperature and water content below 130 cm by interpolation. These observed values ​​and estimated values ​​are used as the initial values ​​of soil variables in the Noah-MP model. The vertical distribution of the observed perennial warm grass root biomass can be used as the initial value of the vegetation variable. Collect the soil parameters required for the operation of the Noah-MP model.

[0216] Step 23, collect the soil parameters of the Santa Rita grassland site required for the calculation of the soil organic carbon decomposition model in this embodiment (see Table 3). The observed total organic carbon density distribution on the 0-43.2 cm vertical profile of the soil was collected, and the values ​​without observation in the deep layer were estimated by interpolation; based on the average proportion of each carbon pool and total organic carbon observed at multiple other sites, the density of each carbon pool in each layer of soil on the soil profile was preliminarily calculated as the initial value for the operation of the organic carbon decomposition model.

[0217] Table 3. Soil parameters at Santa Rita Meadows Station, USA

[0218]

[0219] Step 24, repeat the atmospheric forcing data of Santa Rita grassland site in 2007 and run the Noah-MP coupled model continuously until the soil temperature, water content, O2, CO2 concentration and the density of each soil carbon pool reach equilibrium (the temporal variation mode of each year is almost the same). At this time, the calculated values ​​of the above variables in the deep soil are used as the model initial values ​​estimated before but not from observations, and then the coupled model is run again for one year with the atmospheric forcing data in 2007 to calculate the size of each carbon pool in each layer of soil every half hour, the rate of CO2 release by soil microbial heterotrophic respiration, soil CO2 concentration and surface CO2 flux.

[0220] Step 25, collect the soil CO2 concentration at 2cm and 10cm depth and surface CO2 flux observed at the Santa Rita grassland site in 2007. The observed half-hourly 5cm and 10cm soil temperature, volumetric water content, 2cm and 10cm soil CO2 concentration and surface CO2 flux are compared with the simulated values ​​of the coupled model, and the Nash-Sutcliff efficiency (ME), root mean square error (RMSE) and correlation coefficient (R) are calculated. Figure 4 As shown in be, we can see the comparison between the simulated and observed values ​​of soil temperature and volumetric water content at 5cm and 10cm every half hour. Figure 5 As shown in the figure, we can see the observed (blue dashed line) and simulated (red solid line) soil surface CO2 flux (a), 2cm (b) and 10cm (c) soil CO2 concentration every half hour in 2007. The specific example calculates the change of the carbon pool size of the top 13cm soil of the Santa Rita grassland site over time in 2007. Figure 6 Shown are the simulated changes in the density of DOC (a), MBC (b), MAOC (c), ENZ (d) and POC (e) in the 13 cm soil layer on the surface every half hour. The black line is the overall carbon pool density, and the blue and red lines are the carbon pool densities in the wet and dry areas per unit volume of soil.

[0221] like Figure 7 The figure shows the vertical distribution of MAOC in the simulated case of considering and not considering the vertical transport of DOC by soil water flow at the end of 2007. When considering the vertical transport of DOC by soil water flow, the simulated MAOC density at a depth of 55 cm in the soil (green line) is significantly greater than the value without considering it (blue line).

[0222] The model established in the present invention is a model based on the physical and chemical mechanism of earth organisms, which describes the processes of microorganisms in different activity states of soil producing extracellular enzymes, growth, respiration and death, describes the process of extracellular enzyme catalytic decomposition of POC into DOC and active microorganisms absorbing and utilizing DOC, describes the process of mineral adsorption and desorption of DOC and vertical transport of DOC to the deep soil by water flow to form MAOC, so the speed of organic carbon decomposition and release of CO2 at different depths in the soil and the size of each carbon pool of organic carbon can be calculated. Coupling the model with the land surface process model can more accurately simulate the CO2 concentration at different depths of the soil at the Santa Rita grassland site and the surface CO2 flux, especially the pulsed soil respiration changes caused by dry and wet changes, showing good simulation ability. The model is combined with the earth system model to simulate the long-term changes in the soil MAOC carbon pool, and thus can predict the long-term storage capacity of soil for organic carbon under future climate change conditions.

[0223] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0224] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for establishing a soil organic carbon decomposition model based on microbial processes, characterized in that: The method for establishing the soil organic carbon decomposition model based on microbial processes includes: Step 1: Collect soil and model parameters, define the carbon pool in the dry and wet areas of the model and the physiological status and activity of microorganisms; Step 2: Calculate the speed of carbon pool conversion between dry and wet areas caused by changes in soil water content per unit volume; Step 3, calculate the rate of enzyme-catalyzed decomposition of POC to form DOC in the dry and wet areas, and the rate of DOC absorption by active microorganisms in the wet area; Step 4, calculate the rates of microbial extracellular enzyme production, growth, respiration and death in dry and wet areas, as well as the MAOC density in the wet area of ​​the soil at equilibrium; Step 5, establish the mass balance equation of enzyme carbon pool ENZ in dry and wet areas and soil particulate organic carbon POC in unit volume of soil; Step 6, establish the mass balance equation of dissolved organic carbon DOC and mineral-bound organic carbon MAOC in dry and wet areas per unit volume of soil; Step 7, establishing the mass balance equation of the MBC carbon pool of microbial biomass in dry and wet areas of unit volume of soil; Wherein, in step 4, the MAOC density in the soil wet area at equilibrium is calculated using the Langmuir adsorption function according to the DOC concentration of the soil solution; When the solid-liquid two-phase adsorption and desorption reaches equilibrium, the Langmuir adsorption function is used to describe the MAOC density per unit volume of wet area. The relationship with the change of soil solution DOC concentration is: (24) in is the soil bulk density, is the binding affinity parameter, It is the maximum amount of DOC adsorbed by minerals per unit volume of soil; In step 6, the wet zone MAOC density is mainly affected by the adsorption-desorption process of DOC and the MAOC transition between dry and wet zones; thus, the soil wet zone MAOC mass balance equation per unit volume of soil is established: (31) The MAOC density in the dry area is affected by the transformation of MAOC between the dry and wet areas. The mass balance equation of MAOC in the dry area per unit volume of soil is as follows: （32）。 2. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 1, characterized in that: In step 1, the carbon pools in the dry and wet areas of the model are defined according to the soil volumetric water content. The total soil organic carbon includes the following five carbon pools: particulate organic carbon POC, mineral-bound organic carbon MAOC, dissolved organic carbon DOC, microbial carbon MBC, and extracellular enzymes ENZ; , , and They are the total density of the four carbon pools per unit volume of soil; since soil organic carbon exists in soil pores, the soil pores are defined as The volume space occupied by the water is the wet area, and its size is the volumetric water content ; The space occupied by air is the dry area, and its size is ; The soil carbon pool in the dry area is called the dry area carbon pool, and the soil carbon pool in the wet area is called the wet area carbon pool; the four different types of carbon pools, DOC, MAOC, MBC, and ENZ, are divided into dry and wet carbon pools respectively; the wet carbon pool , , and They are the density of the four carbon pools per unit volume in the wet area, the dry carbon pool , , and are the densities of the four carbon pools per unit volume in the dry area; therefore, the overall density of the soil carbon pool per unit volume is the sum of the product of the carbon pool density in the dry and wet areas of the pore microenvironment and the volume of each area. For the DOC carbon pool, it can be written as: (1) The above form is also applicable to MAOC, ENZ and MBC carbon pools; The overall density of POC carbon pool per unit volume of soil The density of particulate organic carbon in soil pores The relationship is as follows: (2) 。 3. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 2, characterized in that: In step 1, the activity or potential activity and dormancy of microorganisms and their physiological activities are defined according to the dry and wet areas. Since the activity of microorganisms is inseparable from the soil solution, the microorganisms in the wet area are defined as active or potentially active, and in the dry area as dormant. Only the active microorganisms in the wet area can absorb and utilize the DOC in the wet area solution of the soil through DOC diffusion and produce extracellular enzymes. Potentially active microorganisms cannot absorb DOC and do not produce extracellular enzymes. Dormant microorganisms in the dry area cannot absorb DOC, do not produce enzymes, and do not die.

4. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 3, characterized in that: In step 2, when the water content increases, part of the dry area becomes a wet area, and this part of the dry carbon pool becomes part of the wet carbon pool; and for the microbial carbon pool, some dormant microorganisms in the dry area enter an active or potentially active state; when the water content decreases, part of the wet area becomes a dry area, and this part of the wet carbon pool becomes part of the dry carbon pool; and for the microbial carbon pool, some active or potentially active microorganisms in the wet area enter a dormant state; when the water content increases or decreases, the speed of conversion between the dry and wet areas of the four carbon pools in a unit volume of soil , , and is the product of the volumetric water content change rate and the carbon pool density in the dry or wet area; for the DOC carbon pool, It can be expressed as: (3) The above formula is also applicable to MAOC, ENZ and MBC carbon pools.

5. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 4, characterized in that: In step 3, the Michaelis-Menten kinetic equation is used to calculate the rate of enzyme-catalyzed decomposition of POC to form DOC in the dry and wet areas and the rate of DOC absorption by active microorganisms in the wet area, and the Arrhenius equation is used to calculate the effect of temperature on the decomposition rate and absorption rate; The rate at which POC per unit volume of soil is decomposed into DOC by enzymes , which is determined by the volume of the dry / wet area in the soil pores and the POC catalytic decomposition rate in the dry and wet areas. and Decision: (4) and is determined by the POC concentration and described by the Michaelis-Menten kinetic equation, which is proportional to the concentration of each enzyme: (5) (6) in It is the maximum rate at which POC is enzymatically degraded to form DOC at a unit concentration when the substrate concentration does not limit the reaction rate. is the half-saturation constant of the Michaelis-Menten kinetic equation, that is, the substrate concentration when the reaction rate is half of the maximum reaction rate; is the catalytic efficiency of the enzyme in the dry area. Compared with the wet area, the catalytic efficiency is reduced due to the fixation of the enzyme in the dry area. The Arrhenius equation is used to calculate the temperature Impact on it: (7) in At the reference temperature The maximum rate of enzymatic decomposition and polymerization of POC per unit concentration, is the activation energy required for depolymerization of POC, is the universal gas constant; Wetland DOC is the DOC dissolved in the soil solution, so the wetland DOC density is expressed as the solution DOC concentration; the rate at which active microorganisms in the wetland absorb and assimilate DOC per unit volume It is determined by the soil solution DOC and pore air O2 concentration and is described by the Michaelis-Menten kinetic equation; It is also proportional to the density of active microbial biomass and is calculated as follows: (9) in It is the maximum rate of DOC absorption by microorganisms per unit concentration when the concentration of DOC and O2 does not limit the absorption rate. is the carbon pool density of active microorganisms per unit volume of wetland area, is the O2 concentration in soil air; and are the half-saturation constants of the Michaelis-Menten equation for DOC and O2 concentrations, respectively; Using the Arrhenius equation to calculate temperature right Impact: (10) in At the reference temperature The maximum rate at which microorganisms absorb DOC at a unit concentration; It is the activation energy required for microorganisms to absorb DOC.

6. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 5, characterized in that: In step 4, the production of extracellular enzymes and the required respiration, maintenance respiration, growth and growth respiration, and death rates of microorganisms in the wet zone of the soil are calculated, and the maintenance respiration rate of dormant microorganisms in the dry zone is calculated; The rate of extracellular enzyme production by active microorganisms in wet soil areas It is proportional to the speed at which active microorganisms absorb and assimilate DOC and can be calculated as: （12） in, The constant percentage of enzyme produced to DOC assimilated by active microorganisms; the respiration rate required to produce extracellular enzymes The calculation is as follows: （15） in is the efficiency of carbon utilization by microorganisms; The DOC absorbed and assimilated by active microorganisms in the wet soil area is used to produce extracellular enzymes and the remaining part after the required respiration must first be used to maintain respiration; the maintenance respiration rate of active microorganisms and its MBC density The Arrhenius equation is used to describe the temperature effect, which is calculated as follows: （16） in, is the maintenance respiration rate per unit microbial mass at the reference temperature, It is the activation energy required by microorganisms to maintain physiological activities; If the remainder of the above After meeting the requirement of maintaining respiration, it can also be used for the growth of microorganisms and the required growth respiration. , the growth rate of active microorganisms in wet areas The calculation is as follows: (17) The required respiration rate for growth The calculation is as follows: （18） If the remainder of the above It can only be used to maintain more than half of the respiration, but not all of it. At this time, the active microorganisms are in a state of starvation and need to consume their own biomass to meet all of the respiration. If the remaining part cannot meet half of the respiration, the active microorganisms in the starvation state begin to enter a potential activity state. At this time, the microorganisms stop absorbing DOC and stop producing extracellular enzymes. The respiration is two orders of magnitude lower than that in the active state, and the death rate is one order of magnitude lower than that in the active state. and are the biomass carbon density when the wet zone microorganisms are active and potentially active, respectively, and can be expressed as （19） Maintenance respiration rate of potentially active microorganisms in wet areas The calculation is as follows: （20） Among them, the reduction factor , b indicates that the maintenance respiration rate of potentially active microorganisms is only one percent of that in the active state; Use the first-order kinetic equation to describe the death rate of microorganisms in the unit volume of wet area when they are active and potentially active : （21） in is the death rate constant of active microorganisms, It is a factor that reduces the rate of death of potentially active microorganisms; Maintenance respiration rate of dormant microorganisms in dry zone microenvironment , is one percent of the active state and is calculated as follows: （22）。 7. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 6, characterized in that: In step 4, calculate the rate of CO2 release by heterotrophic respiration of microorganisms per unit volume of soil. ; Respiration is maintained by active or potentially active microorganisms in wet areas or , respiration required for the production of extracellular enzymes by active microorganisms and growth breathing and the maintenance of respiration of dormant microorganisms composition: （23）。 8. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 1, characterized in that: In step 5, the enzymes in the wet zone of soil are produced by active microorganisms, which are reduced due to inactivation. At the same time, the enzyme carbon pool between dry and wet zones changes due to changes in water content. The mass balance equation of enzymes per unit volume in the wet zone of soil is established: （25） in, is the turnover constant of enzyme inactivation in the wet zone. The enzyme inactivation is described by the first-order kinetic equation. The inactivated enzyme enters the DOC pool in the wet zone. The enzymes in the dry area are reduced due to inactivation. At the same time, the conversion of enzyme carbon pools between dry and wet areas is changed due to changes in water content. Compared with the enzymes in the wet area, the dry area has no water, which leads to a decrease in the inactivation rate of the enzymes. Therefore, the mass balance equation of the enzymes in the dry area per unit volume of soil is established: （26） in, is the reduction factor of the enzyme inactivation rate in the dry zone.

9. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 8, characterized in that: In step 5, particulate organic carbon (POC) mainly comes from plant litter and a part of dead microorganisms, and decreases as it is decomposed into DOC by enzymes. Thus, the POC mass balance equation per unit volume of soil is established: （27） in, It is the part of dead microorganisms converted into POC. is the input item of vegetation litter entering the soil carbon pool per unit time, It is the portion of vegetation litter input into POC.

10. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 9, characterized in that: In step 6, the DOC in the wet zone solution mainly comes from the catalytic decomposition of POC, the inactivation of enzymes, part of dead microorganisms and plant litter, and plant root secretions. It decreases as active microorganisms absorb DOC and is affected by the transition between dry and wet zone DOC, the adsorption-desorption process, and the vertical transport of DOC by soil water. Therefore, the mass balance equation of DOC in the wet zone solution per unit volume of soil is: (29) in, It is the input rate of DOC contained in plant root exudates per unit volume of soil. Since the input of exudates into the soil requires soil water, it is assumed that all of them enter the wet zone. It is the sum of the amount of DOC adsorbed on the mineral surface in the unit volume of soil per unit time (-) and the amount of DOC desorbed by MAOC into the solution (+). is the vertical transport flux of DOC by soil water; The DOC in the dry area comes from the catalytic decomposition of POC, the inactivation of enzymes in the dry area, and part of the litter, and is affected by the DOC transformation between the dry and wet areas. Therefore, the mass balance equation of DOC in the dry area per unit volume of soil is: (30) 。 11. The method for establishing a soil organic carbon decomposition model based on microbial processes according to claim 1, characterized in that: In step 7, when the DOC absorbed by the active microorganisms in the wet zone can be used for growth, their biomass will decrease due to death. At the same time, the conversion of biomass between dry and wet zones will change due to the change in water content. Therefore, the mass balance equation of MBC of active microorganisms in the wet zone per unit soil can be written as: (33) The mass balance equation of active microorganisms in the hungry state in the wet area of ​​unit volume of soil can be written as: (34) The potentially active microorganisms in the wet zone not only consume their own biomass to maintain respiration, but also reduce their biomass through death. At the same time, the conversion of biomass between dry and wet zones changes due to changes in water content. The mass balance equation of the potentially active microorganisms MBC in the wet zone per unit volume of soil is: （35） The dormant microorganisms in the dry zone are in a very low state of maintaining respiration, which requires consumption of their own biomass. At the same time, the conversion of biomass between dry and wet zones is changed due to changes in water content. The mass balance equation of dormant microorganisms in the dry zone per unit volume of soil is: （36）。

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