Carbon is the basic element that constitutes living organisms, is the core of all organic matter, distributed in the ocean, soil, vegetation, atmosphere and other reservoirs, soil is the largest carbon reservoir in terrestrial ecosystems. Soil carbon not only affects the storage and storage of nutrients in soils, but also plays a vital role in the global carbon cycle. It has many forms, mainly including inorganic carbon and organic carbon, and today Xiaopu will introduce soil carbon to you from these two aspects!
Soil inorganic carbon
Soil inorganic carbon (SiC) is:Refers to various carbon-containing inorganic compounds in the soil in negative valenceIt is mainly a mineral carbonate formed in the weathering process of the parent rock in the soil, and its accumulation rate is very fast, and it is easily affected by factors such as atmosphere, water salinity, etc., mainly in arid and semi-arid areas, which not only affects the soil pH value, fertilizer supply capacity and soil environmental quality, but also has a certain effect on alleviating soil heavy metal pollution. It is mainly classified from two aspects: existence form and **, as follows:
According to different forms of existence: it is divided into gaseous soil CO2, liquid CO32- solution and solid carbonate, and the amount of gaseous and liquid inorganic carbon in the soil is less than that of solid carbonate, so it is considered that the main component of soil inorganic carbon is carbonate. According to different **: divided into primary carbonate and secondary carbonate. Primary carbonate** is a natural preserved carbonate without weathering and soil-forming in the parent material or host rock. Secondary carbonate is formed by the weathering of the soil, and the carbonate formed by the dissolution of primary carbonate and CO2 and water in the soil is formed through a series of chemical reactions.
Soil organic carbon
Soil organic carbon (SOC) is a general term for carbon-containing organic matter formed by microorganisms after organic matter such as animal and plant residues and root exudates in the environment enter the soil。It is the main component of soil carbon, mainly derived from dead biological residues and organic materials such as livestock manure and green manure, and is an important indicator to measure soil fertility, and plays an important role in soil nutrient cycling, improving soil fertility, maintaining and consolidating soil structure.
There are many classification methods of soil organic carbon, and different grouping methods are quite different. According to the differences in the principles and properties of different grouping methods, these methods are roughly divided into three categories: physical grouping, chemical grouping and biological grouping. 
Physical groupingPhysical grouping is to separate soil organic carbon components with different activities by disintegration, dispersion, density centrifugation and sedimentation, which are mainly classified from three aspects: relative density, soil particle size or soil aggregates.
(1) Density groupingIt refers to the soil being centrifuged in a heavy liquid, and the light organic carbon floating on the surface of the liquid is recombinant organic carbon. Light Group Organic Carbon (LFOC):Refers to the microbial structure that can observe fungi and actinomycete spores, accounting for 15%-32% of the total soil organic carbon, mostly from plant debris, plant roots and charcoal, and the chemical composition is mostly carbohydrates and amino acids. It is primaryReflects the impact of short-term land use patterns on organic carbonRecombinant organic carbon (HFOC):The main component is humus, which exists in the form of organic-inorganic complexes in the soil, and its content generally accounts for 70% to 80% of the total organic matter content. itreflects the ability of the soil to hold organic carbon
(2) Particle groupingIt refers to the use of sodium hexametaphosphate or ultrasound to disperse the soil according to the particle size difference, where 0053mm particles, as granular organic carbon, will <0053mm particles as mineral-bound organic carbon.
Particulate organic carbon (poc): It is mainly produced by plant activities, including a large amount of plant-derived carbon, which is the organic carbon part combined with sand particles (53-2000 m), which belongs to the slow carbon pool in the organic carbon pool, mainly in the decomposition products of plant residues with medium decomposition rate, and organically combines with soil aggregates. It is a transitional component in the transformation of fresh organic matter to humus, which is a relatively easy to decompose and biologically active component in the soil organic carbon pool, and is also considered to be a non-protective part of organic carbon.
The mineral-bound state is organicCarbon (MAOC):It is produced by the activities of microorganisms, in which microbial carbon accounts for a large proportion and is relatively stable, which plays an important role in the stability of soil organic carbon. It is closely related to the aggregate-bound carbon, which affects the dynamic change of soil organic carbon, isIt is one of the important mechanisms of soil organic carbon sequestration
(3) Grouping of aggregates, which are divided into 2 categories according to their particle size: macroagglomerates (particle size 250 m) and microaggregates (particle size < 250 m). Soil aggregates are the basic units of soil structure, which play a protective role in soil organic carbon, hinder the contact between microorganisms and substrates, reduce and inhibit microbial activities, and play an important role in the process of soil formation.
Chemical groupingInitially, the chemical classification of soil organic carbon was mainly humus, but at present, the classification is mainly based on the different oxidation, solubility and hydrolysis properties of carbon components in various extractants. (1) Classification according to the composition of the substanceSoil humus (HS):It is a kind of macromolecular organic matter with no fixed molecular structure formed by the decomposition of animal and plant residues through a series of physical, chemical and biological actions, accounting for about 60%-90% of the total soil organic matter. Humus is very important in maintaining soil fertility, protecting the ecological environment, and ensuring the sustainable development of agriculture.
According to the difference in acid-base solubility, it is divided into humic acid (HA), fulvic acid (FA) and humin (HM). Among them, fulvic acid and humic acid are the main components of humus, which are collectively referred to as humic acid. Humin is the most closely bound to soil minerals, mainly in the form of organic-inorganic complexes, and belongs to inert humus. (2) Classification according to chemical solventsOxidizing organic carbon (ROC).: Refers to organic carbon that can be oxidized by 333mmol LKMNO4. It accounts for 13%-28% of soil organic carbon, provides energy for plant growth and soil microbial activities, is easy to decompose, oxidize and mineralize in soil, has a short turnover time, participates in a large range of carbon cycles, and can be sensitiveIt reflects the subtle changes of community vegetation and soil environment in the early stage. YesDissolved Organic Carbon (DOC):It means that the aperture that can pass through is 0The 45 m filter membrane is a unity of organic molecules with different structures, and the main components are proteins, amino acids, macromolecular humus and carbohydrates. As a relatively active organic carbon component in terrestrial ecosystems, it can not only be adsorbed by mineral soil, but also enter the water environment with the movement of soil moistureThe soil sphere is an important material form that connects the other spheres. Acid hydrolysis of organic carbon: Acid hydrolysis refers to the use of sulfuric acid and hydrochloric acid as extraction agents to extract amino acids, amino sugars, carbohydrates and other substances from the soil. Acid hydrolysis divides acid hydrolyzed organic carbon into active organic carbon andInert organic carbonto calculate the inertness index and measure the size of the inert organic carbon pool. Biological groupingBiological taxonomy divides soil organic carbon into microbial biomass carbon and biological potentially mineralizable carbon.
Microbial biomassCarbon (SMBC):It refers to the carbon contained in live bacteria, fungi, algae and soil microorganisms in the soil that is less than 5-105 m3, and is the most active part of the organic carbon in the soil. It accounts for a small proportion of the soil, directly participates in soil metabolism and decomposition, and is a vital part of the soilIt reflects the size of soil assimilation and mineralization capacity, and is a sign of soil activity.
Biological Potential Mineralizable Carbon (PMC):That is, the amount of CO2 produced per unit of microbial mass during the decomposition of organic matter by microorganisms. The high value represents the activity of fermentation microflora, and the low value reflects the activity of homeostatic indigenous microflora, which is also one of the important measures to evaluate soil fertility and plays a vital role in the whole carbon cycle.
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