A review of the composition of soil carbon pool

The soil carbon pool is the biggest one in the terrestrial ecosystem. The composition of soil carbon pool influences carbon accumulation and decomposition,and directly controls global terrestrial carbon balance,and influences soil quality.Making clear the constitutes of soil carbon pool is the key process in revealing the mechanism of soil carbon pools change.This paper overviewed the structure and composition of the soil carbon pools. Soil carbon pools include soil inorganic carbon pool and soil organic carbon pool. Soil inorganic carbon pool includes HCO-3in soil solution,CO2 in soil air,and CaCO3 in soil. And CaCO3 is the main component in soil inorganic carbon pool. Soil inorganic carbon pool can influence soil organic carbon pool by affecting composition of soil aggregates,microbial activity,soil pH,and soil organic matter decomposition rate. Soil organic carbon is a very complex continuous mixture,which includes a variety of organic carbon fractions and forms with different nature. And the content of all kind of soil organic carbon affects the transformation of soil carbon pool and thereby influences soil quality and carbon cycle in terrestrial ecosystem. Soil organic carbon pools are categorized into soil labile organic carbon pool and soil stable organic carbon pool. Among them,soil labile organic carbon can turnover within a certain time,and can be utilized by plant and microorganism,and have a major impact on the carbon balance. Soil labile organic carbon is also named soil activated organic carbon or effective carbon by some authors,and includes terms as available carbon( AC),dissolved organic carbon( DOC),water soil organic carbon( WSOC),readily oxidation carbon( ROC),microbial biomass carbon( MBC),biodegradable carbon,light fraction organic carbon( LFOC),particulate organic carbon( POC) and so on. Black carbon( BC) and coal carbon are suggested to be categorized into soil organic carbon pool to perfect the frame of soil organic carbon pool composition. Black carbon is a C-rich organic material derived from incomplete combustion of fossil fuels and vegetation and from weathering of graphitic C in rocks,and very stabile.Black carbon captures and sequesters carbon from the bio-atmospheric cycle,which,in the long term,reduces greenhouse gas emissions and thus mitigates the greenhouse effect. Meanwhile,resistant black carbon amendation increase soil organic matter,thus regulating soil structure and enhancing soil fertility. Because of its high adsorption capacity,black carbon adsorbs organic pollutants,heavy metals,nutrients to decrease ecosystem risk. The coal( carbon) in the surface layer soil mainly come from outside source; include garbage,filling,atmospheric sedimentation and so on. The coal mine area is usually the district absorbing the most coal( carbon). In future studies,we should strengthen the researches on the scientific issues including the chemical composition,overlapping quantitative relationship of the soil organic carbon pools,transformation and migration of soil organic carbon in the soil,the impact of black carbon on the stability of the soil carbon pool and soil quality,the impact of coal( carbon) on soil quality and environmental effects in the coal mining disturbed zone,and organic carbon change and mechanism in newly developed soil,reclamation soil and reconstruction soil.