A method for estimating the efficiency of litter decomposition input of organic carbon into soil

Abstract

The present invention belongs to the technical field of litter decomposition, and discloses a method for estimating the efficiency of inputting organic carbon into the soil through litter decomposition. The sampling point selection of the present invention is flexible, which is convenient for conducting experiments. The PVC ring method is used to monitor litter decomposition, which enables the litter to be in direct contact with the soil, ensuring good ventilation to promote the normal metabolic activities of microorganisms during the decomposition process, and can better simulate the actual conditions in different ecosystems, thereby improving the applicability and universality of the method. At the same time, the part of carbon lost in the gaseous state during the decomposition of litter can be dynamically monitored, thereby accurately evaluating the input efficiency of organic carbon into the soil, and providing a scientific basis for improving the carbon sequestration function of forest soil and the sustainability of the ecosystem.

Description

Technical Field

[0001] The present invention belongs to the technical field of litter decomposition, and more particularly relates to a method for estimating the efficiency of inputting organic carbon into soil through litter decomposition. Background Art

[0002] Soil is the largest organic carbon reservoir on land and has enormous carbon sink potential. Even small fluctuations in soil can cause significant changes in the global carbon cycle, thereby affecting climate change. More than 40% of organic carbon in terrestrial ecosystems is stored in forest soils. Litter input is the main source of carbon (C) and nutrient pools in forest soils and regulates soil biogeochemical processes and microbial communities in terrestrial ecosystems. Therefore, it is extremely necessary to accurately reveal how litter input affects soil organic carbon in forest ecosystems. This is particularly urgent and necessary for predicting the storage and release dynamics of forest soil carbon sinks under global change scenarios.

[0003] Previous studies can be roughly divided into two research methods: one is based on indoor simulated litter decomposition experiments, which usually place litter decomposition under controlled conditions in the laboratory, and can arbitrarily design experiments according to personal research purposes to obtain relevant indicator values ​​in a relatively short time (Zhang Huihui, Bai Yunyu, Zhang Yingjie, et al. Ecological stoichiometric characteristics of litter in the tundra zone of Changbai Mountain and its response to simulated nitrogen deposition [J]. Acta Ecologica Sinica, 2022, 42(21): 8795-8808; Yang Na, Wang Simin, Yu Lelin, et al. Effects of alternating dry and wet conditions on the amount and characteristics of dissolved organic carbon in litter sources of common tree species in subtropical plantations [J]. Journal of Ecology, 2023, 42(12): 2895-2902.). Another method is to use the net bag method in the field to study the litter decomposition process (Gai He, Zhu Wenwen, Zhang Min, et al. Effects of secondary salinization on stream benthic decomposers and litter decomposition [J]. Journal of Water Ecology, 2024, 45(03): 32-44; Li Huixuan, Ma Hongliang, Yin Yunfeng, et al. Dynamic characteristics of active and inert carbon and nitrogen during litter decomposition in subtropical natural broad-leaved forests [J]. Acta Plant Ecologica Sinica, 2023, 47(05): 618-628.), but because the net bag will limit the oxygen contact on the surface of the litter, thereby affecting the respiration of microorganisms during the decomposition process, the decomposition rate may be different from the decomposition rate under natural conditions, and this method reflects an idealized and theoretical result. During the decomposition of litter, part of the organic carbon is released into the atmosphere in the form of gas through the respiration of microorganisms, while the other part forms organic carbon through a series of turnovers under the action of microorganisms (Su Zhuoxia, Su Bingqian, Shangguan Zhouping. Research progress on the impact of plant litter decomposition on soil organic carbon stability [J]. Research on Soil and Water Conservation, 2022, 29(02): 406-413; Zhou Zhenghu, Liu Lin, Hou Lei. Stability and formation of soil organic carbon: mechanism and model [J]. Journal of Beijing Forestry University, 2022, 44(10): 11-22.).When researchers study litter decomposition in the wild, they often ignore the gaseous carbon and only detect the carbon input into the soil during litter decomposition. They then compare it with the soil organic carbon in the control group (Xu MP, Zhi RC, Jian JN, et al. Changes in Soil Organic C Fractions and C Pool Stability Are Mediated by C-Degrading Enzymes in Litter Decomposition of Robinia pseudoacacia Plantations[J]. Microbial Ecology, 2022: 1-11.) to analyze the amount of organic carbon input into the soil during litter decomposition. Therefore, the conclusions obtained deviate from the actual organic carbon obtained in the soil.

[0004] Therefore, it is very meaningful to monitor the carbon dioxide produced by soil respiration during the decomposition of litter in the wild. At the same time, it is also very important to calculate the actual organic carbon content input into the soil by litter decomposition. Both are problems that technical personnel in this field urgently need to solve. Summary of the Invention

[0005] To overcome the shortcomings and deficiencies of existing technologies, this paper provides a method for estimating the efficiency of litter decomposition into soil organic carbon. This method incorporates diverse monitoring techniques, such as respirometry to measure gaseous carbon content, to fully understand the dynamic changes in organic carbon during litter decomposition. This method effectively overcomes the limitations of existing monitoring methods and provides new technical means and data support for studying litter-to-soil organic carbon input, thereby promoting research on ecosystem carbon cycling and sustainable soil management.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for estimating the efficiency of litter decomposition in inputting organic carbon into soil comprises the following steps:

[0008] (1) Determine the research area and select the appropriate forest type;

[0009] (2) Sample point layout: based on the geographic information system and actual field investigation, the sampling points were located using a handheld GPS, a compass, and a topographic map of the sample point distribution;

[0010] (3) After the sampling point is located, the surface humus and litter are removed, the topsoil layer is exposed, and several PVC rings are embedded in the soil. According to the average litter biomass of the study area over the years, litter of known weight is placed in the PVC ring, and then a dustproof net is fixed above the PVC ring to prevent the entry of external litter. At the same time, a bare soil control experiment with the same conditions is set up, except that no litter is placed in the PVC ring.

[0011] (4) Regularly monitor the amount of carbon dioxide produced by soil respiration, soil moisture, and temperature within the PVC ring using a soil respirometer;

[0012] (5) Sampling was carried out regularly on the agreed date. When sampling, all the remaining litter in the PVC ring was first taken, and then the soil sample under the litter was taken. The soil of the control group was taken in the same way;

[0013] (6) Sample testing: The collected litter was dried, weighed, and sieved, and then the carbon and nitrogen contents of the litter were measured using an elemental analyzer; the air-dried soil sample was sieved, and the organic carbon content was determined using the potassium dichromate-sulfuric acid oxidation method;

[0014] (7) Calculate the litter mass loss using the following formula:

[0015] M=(M0-M t ) / M0×100%

[0016] Where: M is the weight loss rate; M0 is the dry weight of litter at the beginning of decomposition; M t To decompose the dry weight of litter at a certain time point;

[0017] The mass of organic carbon input to the soil by litter decomposition is calculated using the following formula:

[0018] TOC si =[TOC li -CO2-C li ]-[TOC cki -CO2-C cki ]

[0019] Where: TOC si is the mass of organic carbon input to the soil by litter decomposition (mg), TOC li It is the sum of soil organic carbon input by litter and existing soil organic carbon (mg), CO2-C li is the total amount of gaseous organic carbon produced by leaf respiration and soil respiration (mg), TOC cki is the organic carbon in the soil (mg), CO2-C cki is the gaseous organic carbon produced by soil respiration (mg);

[0020] The efficiency of litter decomposition in inputting organic carbon into the soil is calculated using the following formula:

[0021]

[0022] Where: η i is the efficiency of litter decomposition inputting organic carbon into the soil (%), TOC si is the organic carbon input into the soil by litter (mg), TOC li It is the sum of soil organic carbon input by litter and existing soil organic carbon (mg), CO2-C li It is the total amount of gaseous organic carbon produced by leaf respiration and soil respiration (mg).

[0023] Preferably, the height of the PVC ring in step (3) is 20 cm, the diameter is 20 cm, the depth of the PVC ring embedded in the soil is 10 cm, and the height exposed to the soil surface is 10 cm.

[0024] The beneficial effects of the above technical solution are: the soil ring height is the distance from the soil surface to the upper end of the soil ring. The soil ring height determines the volume of the air chamber measured by the fully automatic portable respirator. The embedded PVC ring should be selected on a relatively flat surface, so the soil ring height is set to 10 cm.

[0025] Preferably, the sampling depth of the soil sample in step (5) is 10 cm.

[0026] As can be seen from the above technical solution, compared with the prior art, the present invention provides a method for estimating the efficiency of litter decomposition and input of organic carbon into the soil, which has the following beneficial effects:

[0027] (1) The sampling point selection of the present invention is highly flexible and convenient for conducting experiments. The PVC ring method is used to monitor litter decomposition, which enables the litter to directly contact the soil, ensuring good ventilation to promote the normal metabolic activity of microorganisms during the decomposition process. It can better simulate the actual conditions in different ecosystems and improve the applicability and universality of the method. At the same time, the part of carbon lost in the gaseous state during litter decomposition can be dynamically monitored, thereby accurately evaluating the input efficiency of organic carbon into the soil, providing a scientific basis for improving the carbon sequestration function of forest soil and the sustainability of the ecosystem.

[0028] (2) The calculation formula of soil organic carbon input in the present invention can take into account the content of gaseous carbon produced by the soil and more accurately calculate the content of organic carbon input into the soil during the decomposition of litter. Soil organic carbon input efficiency η iThe higher the value, the more organic carbon the litter can input into the soil. If a sample has a large amount of organic carbon input from the litter, but the amount of organic carbon already in the soil and the total amount of gaseous organic carbon produced by respiration are low, the sample has a high organic carbon efficiency, indicating that the soil is more efficient in using the litter. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0030] Figure 1 (a) and (b) are the layout diagram of the PVC ring for litter decomposition and the soil respiration monitoring diagram of the present invention, respectively.

[0031] Figure 2 (a) and (b) are the litter decomposition mass loss and C:N ratio of Example 1, respectively.

[0032] Figure 3 This is a graph showing the changes in carbon dioxide flux generated during different processes of litter decomposition in Example 1. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] The research area of ​​the embodiment of the present invention is located in the Shuanglong State-owned Ecological Experimental Forest Farm in the north of the Qiaoshan State-owned Forest Management Bureau in Huangling County, Yan'an City, with geographical coordinates of 108°45'32"~109°1'21" east longitude and 35°33'7"~35°49'30" north latitude. The forest farm has a management area of ​​32,012.57 hectares. It has a warm temperate continental monsoon climate with four distinct seasons: dry and windy spring, cool and rainy summer, rainy autumn, and cold and dry winter. The soil belongs to the gray-brown soil zone, with rich accumulation of soil organic matter, and no obvious calcification and claying of the soil, which is suitable for tree growth. Among them, the coniferous forest area is 6,194.39 hm 2 , the broad-leaved forest area is 25695.49hm 2 The main dominant tree species are Chinese pine, arborvitae, larch, oak, white birch, locust, poplar, hard broad-bread and soft broad-bread.

[0035] Example 1

[0036] A method for estimating the efficiency of litter decomposition in inputting organic carbon into soil comprises the following steps:

[0037] (1) Shuanglong State-owned Ecological Experimental Forest Farm in Yan'an City was selected as the research area. Based on the dominant tree species in Shuanglong State-owned Forest Farm, two typical sample plots, Pinus tabulaeformis (YS) and Quercus acutissima (ML), were selected for layout.

[0038] (2) Sample point arrangement: Based on the ArcGIS 10.2 software platform and actual field investigation, the sampling points were located using a handheld GPS, a compass, and a topographic map of the sample point distribution;

[0039] (3) After the sampling point is located, the surface humus and litter are removed to expose the topsoil layer. A PVC ring with a height of 20 cm and a diameter of 20 cm is embedded into the soil of Pinus tabulaeformis and Quercus acutissima using a rubber hammer. The depth of the PVC ring embedded in the soil is 10 cm, and the height exposed to the soil surface is 10 cm. Since this is a destructive sampling, 32 PVC rings are laid in each of the soils of Pinus tabulaeformis and Quercus acutissima. Figure 1 As shown in the figure, the number of PVC rings needs to be arranged according to the specific requirements of the experimental design. 10g of pine and oak litter were placed in the PVC rings in the Pinus tabulaeformis and Quercus acutissima forests, respectively. At the same time, a bare soil control experiment with the same conditions was set up, except that no litter was placed in the PVC rings.

[0040] Fix a nylon dustproof net on the top of the PVC ring to cover it and prevent the outside fallen matter and soil animals from entering the PVC ring;

[0041] (4) Regularly monitor the amount of carbon dioxide produced by soil respiration, soil moisture, and temperature within the PVC ring using a respirometer;

[0042] (5) Sampling was performed regularly, at 132d, 246d, 328d, and 439d after decomposition. When sampling, all the remaining litter in the PVC ring was first taken, and then the soil sample under the litter was taken. The soil sampling depth was 10 cm. The soil of the control group was sampled in the same way.

[0043] (6) Sample testing: The collected Pinus tabulaeformis and Quercus acutissima leaf litter was dried, weighed, and sieved. The carbon (C) and nitrogen (N) contents of the litter were measured using an elemental analyzer. The air-dried soil samples were sieved and the organic carbon (TOC) content was determined using the potassium dichromate-sulfuric acid oxidation method.

[0044] (7) Calculate the litter mass loss using the following formula:

[0045] M=(M0-M t ) / M0×100%

[0046] Where: M is the weight loss rate; M0 is the dry weight of litter at the beginning of decomposition; M t To decompose the dry weight of litter at a certain time point;

[0047] The mass of organic carbon input to the soil by litter decomposition is calculated using the following formula:

[0048] TOC si =[TOC li -CO2-C li ]-[TOC cki -CO2-C cki ]

[0049] Where: TOC si is the mass of organic carbon input to the soil by litter decomposition (mg), TOC li It is the sum of soil organic carbon input by litter and existing soil organic carbon (mg), CO2-C li is the total amount of gaseous organic carbon produced by leaf respiration and soil respiration (mg), TOC cki is the organic carbon in the soil (mg), CO2-C cki is the gaseous organic carbon produced by soil respiration (mg);

[0050] The efficiency of litter decomposition in inputting organic carbon into the soil is calculated using the following formula:

[0051]

[0052] Where: η i is the efficiency of litter decomposition inputting organic carbon into the soil (%), TOC si is the organic carbon input into the soil by litter (mg), TOC li It is the sum of soil organic carbon input by litter and existing soil organic carbon (mg), CO2-C li It is the total amount of gaseous organic carbon produced by leaf respiration and soil respiration (mg).

[0053] Results and Analysis:

[0054] Figure 2In the study, YS represents the Pinus tabulaeformis group, and ML represents the Quercus acutissima group. It can be seen that the mass loss of both types of litter decreased over time, and the decomposition rate of litter in the early decomposition period (0-132 days) was greater than that in the later stages of the decomposition experiment (246-439 days). In contrast, the decomposition rate of Quercus acutissima leaves was faster. The carbon-nitrogen ratio (C:N ratio) of litter decreased during decomposition at different decomposition sites. Throughout the study, YS leaves maintained a higher C:N ratio than ML leaves, with the initial C:N of YS samples being approximately 55% higher than that of ML samples. We observed that the C:N ratio of the samples decreased significantly during the first 328 days of decomposition, and then gradually stabilized.

[0055] Figure 3 In the data, YS is the Pinus tabulaeformis group, ML is the Quercus acutissima group, YS-CK is the Pinus tabulaeformis control group, and ML-CK is the Quercus acutissima control group. It can be seen that the soil CO2 flux of different treatments has significant differences during the measurement period. All of them show a larger CO2 flux value on the 246th day of decomposition and a smaller flux value on the 439th day. In addition, the daily emission flux of CO2 was monitored and showed that the soil CO2 flux showed a single peak pattern, that is, the highest value appeared at 14:00 and was lower at 8:00 and 18:00. From the perspective of the overall cycle, leaf cover released more carbon dioxide than bare soil. For Pinus tabulaeformis soil, the average soil CO2 flux increased by 17.96% when covered with pine leaves compared with bare soil (YS-CK). For Quercus acutissima soil, the average soil CO2 flux increased by 55.39% when covered with Quercus acutissima leaves compared with bare soil (ML-CK).

[0056] Table 1 Input of soil organic carbon generated during the decomposition of Pinus tabulaeformis leaves

[0057]

[0058] Table 2 Input of soil organic carbon generated during the decomposition of oak leaves

[0059]

[0060] Table 3 Input efficiency of soil organic carbon generated during the decomposition of two leaves

[0061]

[0062] As shown in Tables 1 and 2, both leaf decomposition processes input a significant amount of organic carbon into the soil, with the amount of organic carbon input following a pattern of increasing or decreasing. This suggests that in the initial stages of decomposition, microorganisms rapidly decompose readily degradable substances on the litter surface, resulting in a high input of organic carbon into the soil. However, as these readily degradable substances are consumed, microorganisms require more time and energy to decompose the more difficult-to-degrade components, resulting in a slow input of organic carbon. Furthermore, our research has found that the more organic carbon input into the soil during litter decomposition, the more gaseous carbon is produced. Table 3 shows that the efficiency of the two leaf decomposition processes also follows a pattern of increasing or decreasing. A comparison reveals that oak litter leaves are more efficient at inputting organic carbon into the soil than pinus litter leaves, indicating that oak leaves are more likely to input more organic carbon into the soil. Compared to traditional field monitoring methods, the present invention utilizes a method that monitors the amount of carbon lost to the atmosphere by litter, enabling a more accurate assessment of the organic carbon content of litter input into the soil. Traditional monitoring methods, such as the net bag method, are limited by experimental setup and cannot effectively capture atmospheric carbon loss, resulting in significant errors in soil organic carbon assessments. By monitoring atmospheric carbon loss, this new method not only overcomes this limitation but also enables a comprehensive understanding of the actual contribution of litter to soil organic carbon dynamics, providing a reliable data foundation for accurate assessments of ecosystem carbon balance.

[0063] The research results of the present invention show that the litter decomposition process has a significant impact on soil organic carbon input, especially in forest ecosystems. These findings provide important insights for the field to deepen its understanding of the contribution of litter decomposition to soil carbon dynamics. By comparing research data, it is possible to guide the management of forest ecosystems to enhance their carbon sequestration function, respond to climate change and promote ecosystem recovery. In addition, the study shows that the decomposition characteristics of litter of different tree species, such as the higher organic carbon input efficiency of oak compared to Chinese pine, provide a substantial basis for optimizing forest management strategies, including the selection of tree species that are more conducive to carbon storage and specific measures to promote soil organic carbon accumulation. Through these improvements, the field can more comprehensively understand and utilize the importance of the litter decomposition process to the function of forest ecosystems, thereby providing a scientific basis and technical support for ecological protection and sustainable development.

[0064] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the solutions disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method section.

[0065] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for estimating the efficiency of litter decomposition in inputting organic carbon into the soil, characterized in that: The following steps are involved: (1) Determine the research area and select the appropriate forest type; (2) Sample point layout: based on the geographic information system and actual field investigation, the sampling points were located using a handheld GPS, a compass, and a topographic map of the sample point distribution; (3) After the sampling point is located, the surface humus and litter are removed, the topsoil layer is exposed, and several PVC rings are embedded in the soil. According to the average litter biomass of the study area over the years, litter of known weight is placed in the PVC ring, and then a dustproof net is fixed above the PVC ring to prevent the entry of external litter. At the same time, a bare soil control experiment with the same conditions is set up, except that no litter is placed in the PVC ring. (4) Regularly monitor the amount of carbon dioxide produced by soil respiration, soil moisture, and temperature within the PVC ring using a soil respirometer; (5) Sampling was carried out regularly on the agreed date. When sampling, all the remaining litter in the PVC ring was first taken, and then the soil sample under the litter was taken. The soil of the control group was taken in the same way; (6) Sample testing: The collected litter was dried, weighed, and sieved, and then the carbon and nitrogen contents of the litter were measured using an elemental analyzer; the air-dried soil sample was sieved, and the organic carbon content was determined using the potassium dichromate-sulfuric acid oxidation method; (7) Calculate the litter mass loss using the following formula: M=(M0-M t ) / M0×100% Where: M is the weight loss rate; M0 is the dry weight of litter at the beginning of decomposition; M t To decompose the dry weight of litter at a certain time point; The mass of organic carbon input to the soil by litter decomposition is calculated using the following formula: TOC si =[TOC li -CO2-C li ]-[TOC cki -CO2-C cki ] Where: TOC si is the mass of organic carbon input to the soil by litter decomposition (mg), TOC li It is the sum of soil organic carbon input by litter and existing soil organic carbon (mg), CO2-C li is the total amount of gaseous organic carbon produced by leaf respiration and soil respiration (mg), TOC cki is the organic carbon in the soil (mg), CO2-C cki is the gaseous organic carbon produced by soil respiration (mg); The efficiency of litter decomposition in inputting organic carbon into the soil is calculated using the following formula: Where: η i is the efficiency of litter decomposition inputting organic carbon into the soil (%), TOC si is the organic carbon input into the soil by litter (mg), TOC li It is the sum of soil organic carbon input by litter and existing soil organic carbon (mg), CO2-C li It is the total amount of gaseous organic carbon produced by leaf respiration and soil respiration (mg).

2. The method for estimating the efficiency of litter decomposition input of organic carbon into soil according to claim 1, characterized in that: The height of the PVC ring in step (3) is 20 cm, the diameter is 20 cm, the depth of the PVC ring embedded in the soil is 10 cm, and the height exposed to the soil surface is 10 cm.

3. The method for estimating the efficiency of litter decomposition input of organic carbon into soil according to claim 1, characterized in that: The sampling depth of the soil sample in step (5) is 10 cm.

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