人为土壤有机碳的分布特征及其固定意义

文章在分析不同类型的人为土壤形成过程及其特点的基础上研究了人为土壤有机碳含量、分布年龄与同位素组成特征。结果表明,人为土壤中有机碳的含量分布不同于起源土壤或者相应的非人为土壤,主要体现在有机碳含量降低的缓慢和不规则性以及有机碳含量的相对富集。通过计算证明人为土壤的有机碳密度高于相邻土壤或起源土壤。放射性碳测定表明人为土壤中的有机碳年龄较老,说明了有机碳在这些土壤中存在的相对稳定性。土壤有机碳的稳定同位素组成分析表明,土壤中深层的有机碳与现代有机碳来源不同,也表明了土壤中有机碳的稳定存在。文章还分析了人为土壤中有机碳富集和稳定的可能机制,包括物理、化学和生物学机制,认为就有机碳的固定而言,人为土壤是一种具有最佳管理方式的可持续利用的土壤资源

CHARACTERISTICS OF ORGANIC CARBON DISTRIBUTION IN ANTHROPOGENIC SOILS AND ITS IMPLICATION ON CARBON SEQUESTRATION

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.