农地退耕后土壤和团聚体不同来源有机碳的稳定性及其对环境变化和人为扰动响应是退耕后土壤碳汇功能研究中需要迫切解决的科学问题，也是认识土壤有机碳循环与气候系统反馈作用的重要基础。本项目选取黄土高原退耕农地和未退耕农地为研究对象，利用土壤有机质13C自然丰度的差异辨识退耕地土壤和团聚体原有有机碳和新输入有机碳的分布和矿化，通过野外定位试验和室内模拟实验，研究不同水热变化和人为扰动下土壤和团聚体不同来源有机碳的矿化过程，以明确退耕过程中土壤和团聚体中新输入有机碳和原有有机碳的再分配特征，揭示新输入有机碳对原有有机碳矿化的影响及其制约因素，阐明退耕后土壤和团聚体原有有机碳和新输入有机碳的稳定性及其对环境因子变化和人为扰动的响应特征和适应机理，在此基础上揭示退耕后土壤碳汇功能及其对环境因子的敏感性，为退耕后土壤效应评价和土壤碳汇变化的准确预测提供科学依据。

The origin and stability of organic carbon in total soils and aggregates, as well as their response to environmental changes and human disturbances, are the urgent scientific questions in studying the C sequestration in revegetated farmland, and also important scientific basis for understanding the feedbacks between soil organic carbon cycling and climate system. In this project, by comparing the revegetated farmland and adjacent farmland, the original organic carbon and new input carbon in total soils and aggregates after land-use change will be separated through measuring natural abundance of 13C in soil organic matter. By conducting field and laboratory cultivation experiments, the mineralization of original and new input organic carbon in total soils and aggregates will be determined. The objectives of this project is to understand the origin and the redistribution of soil organic carbon in soils and aggregates and their dynamics during the grain for green project, to study how new input carbon affect the mineralization of original carbon in total soils and aggregates, to clarify the stability of soil organic carbon in both soils and aggregates derived from cropland and revegetated land and their response to environmental changes and anthropogenic disturbance. Based on these studies, we try to understand the capacity of carbon sequestration in revegetated farmland and their sensitivity to environmental factors and human disturbances, which would provide scientific evidences for assessing soil responses and precise predicting carbon sequestration in soils after the grain for green project in the Loess Plateau.