Characterization Of Organic Carbon In Chinese Typical Soils By Carbon Stable Isotopes

In terms of natural resources,soil organic carbon is a crucial strategy for mitigating the greenhouse effect and an important indicator of soil fertility.The study of soil organic carbon storage characteristics is essential for China to achieve the goal of carbon neutrality.In view of the mass fractionation of carbon isotopes in soils,the natural abundance of carbon stable isotopes can be used to effectively characterize the fugacity of organic carbon in soils.This thesis focuses on the fugacity characteristics of organic carbon in surface soils of nine typical farming areas in China,red soil profile soils,and surface soils in urban areas of Beijing using the carbon stable isotope natural abundance technique.（1）TheΔ¹³C values of surface soil aggregates in the nine specific cultivated areas in China show an overall pattern of macro-aggregates<micro-aggregates<silt-clay size class fraction,which validates the’hierarchical development model’and the’embryonic development model’of soil aggregates formation.Organic carbon turnover is more likely to occur between neighboring large aggregates,and tillage facilitates soil organic carbon turnover between different size aggregates.（2）The organic matter at the red soil sampling site LF originates from a mixture of C3 and C4 plants;the organic matter source at sampling sites YJ and SM is dominated by C3 plants.In the direction of increasing depth along the red soil profile,the soil organic carbon content decreases,theδ¹³C value increases,and the distribution is sawtooth-like.The variation ofδ¹³C values<3‰in the profile suggests that this distribution trend is caused by a combination of organic carbon in deeper soils undergoing more microbial decomposition and strong leaching in the red soils.（3）Compared to urban bare-ground soils,greenfield soils have higher organic carbon and nitrogen contents and greater MWD values.TheΔ¹³C results for urban soils in Beijing show that the flow of organic carbon between aggregates is higher in greenfield soils than in bare-ground soils.Theδ¹⁵N andΔ¹³C values in the aggregates both show an increasing trend with decreasing aggregate size;the organic carbon and nitrogen contents have similar distribution patterns in the aggregates,so theδ¹⁵N andΔ¹³C dual isotopes can be used to indicate the turnover of organic carbon between the aggregates.Organic carbon and nitrogen in the surface soil of green areas in urban areas of Beijing were positively correlated with Cr,Zn and Pb.The results of this study will provide basic data for the study of organic carbon fixation effects in different types of soils in China,and provide a scientific basis for the study of organic carbon fugacity using the carbon stable isotope natural abundance technique.