CHARACTERISTICS OF ORGANIC CARBON DISTRIBUTION IN ANTHROPOGENIC SOILS AND ITS IMPLICATION ON CARBON SEQUESTRATION
人为土壤有机碳的分布特征及其固定意义

Landuse related human activities are important factors that affect soil organic carbon turnover and global carbon cycling. Anthropogenic soils were formed by long term and intensified human activities under various natural backgrounds. This paper summarized the peculiarities of pedogenic processes of the major kinds of anthropogenic soils and analysed their main characteristics that can contribute to the increased storage of organic carbon in soils. We found that anthropogenic soils were generally thicker in effective soil depth and higher in organic carbon content, as compared to their originating or neighboring natural soils. The distribution pattern of organic carbon in profile was different from that of natural soils but showing an irregularly decreasing pattern with soil depth. Anthropogenic soils contained relatively high organic carbon in deep part of the pedons. We calculated the densities of organic carbon (kilogram per square meter) of all major anthropogenic soils and found that they were higher than their originating or neighboring counterparts. The ratio of carbon density in surface to that of one meter deep soil body was lower in anthropogenic soils than that of natural soils, showing the contribution of the increased soil depth to total organic carbon storage in anthropogenic soils. The 14 C ages of an ancient Hydragric Anthrosols and typical Irragric Anthrosols showed that organic carbon in these anthropogenic soils were quite old and this indicated the relatively stable existence of organic carbon in anthropogenic soils. δ 13 C data from a typical Irragric Anthrosols also indicated that the buried soil organic carbon had little exchange with modern organic matter, and proved the stability of organic carbon in these soils. This paper suggested several possible mechanisms that could contribute to the increase and immobilization of organic carbon in anthropogenic soils. They include physical fractionation and stabilization, chemical structure change, especially humus composition change under intensive human management and, biological obstruction of microbial decay caused by extraneous contaminants such as heavy metals brought in by human activities. Although the real mechanisms need further studies, the phenomenon that anthropogenic soils can store more organic carbon illustrates that anthropogenic soils are best managed soil resources in terms of their contribution to soil fertility maintenance and meanwhile sequestration of carbon in a global scale. This reminds us that good soil management can make global soil an important carbon sink.