红壤坡面团聚体稳定性对有机碳流失的影响机制

Soil aggregate stability is the dominant factors controlling hillslope soil erosion in the hilly red soil region of southern China. The red soil, however, is developed from different soil parent materials, and its aggregate stability varied substantially. Soil erosion by water involves the processes of detachment, transport and deposition of soil materials by the erosive agents. During raindrop impact soil, aggregates breakdown and produce finer, more transportable particles and micro-aggregates. Sediment transport process is size-selective. Specifically, fine soil particles are preferentially transported while coarse soil particles are prone to deposition. Furthermore, the soil organic carbon in various size of eroded sediments is different. Hence, the aggregate stability may greatly influence the soil organic carbon loss in red soil hillslope. In this study, the typical red soils, developed from quaternary red clays, granite, sandstone, and limestone, respectively, was selected to investigate the soil and water loss on the sloping farmland, identify the eroded sediment size distribution, and compare the aggregate-associated organic carbon between the 4 typical red soils. Results from this proposal may have significant implications for understanding of eroded soil organic carbon dynamics, and may provide new sights and theory basis for eroded soil organic dynamics in the hilly red soil region of southern China.

团聚体稳定性是南方红壤丘陵区坡面侵蚀过程的主控因子，而该区红壤发育于不同成土母质，其团聚体稳定性差异较大。坡面侵蚀过程中泥沙输移对不同粒径大小的团聚体具有分选性，同时由于有机碳在各粒级团聚体的富集程度不同，可能会导致不同红壤类型坡面侵蚀泥沙各粒级有机碳输出的差异。为此，本研究拟选取团聚体稳定性差异较大的第四纪粘土红壤、花岗岩红壤、砂岩红壤和石灰岩红壤，采用野外实地调查和径流试验小区模拟降雨实验，研究不同母质发育红壤坡面的产流、产沙特征，分析不同团聚体稳定性红壤的侵蚀泥沙分选规律，并比较侵蚀泥沙各粒径团聚体有机碳流失的差异，揭示侵蚀泥沙分选与有机碳输出的内在联系，阐明坡面侵蚀条件下团聚体稳定性对侵蚀泥沙各粒径团聚体有机碳输出的影响机制。研究结果有助于深入理解侵蚀过程对土壤有机碳流失的影响机理，也可为南方红壤丘陵区土地质量改善和生态环境保护提供依据。

南方红壤区是我国典型的生态环境脆弱区，由于该区人口密度高、人地矛盾突出，暴雨强度大、雨量多而集中，地形破碎、坡度变化大，陆表风化程度高、风化壳抗蚀性差等导致水土流失非常严重。团聚体稳定性是南方红壤区坡面侵蚀的主控因子，而该区红壤发育于不同成土母质，其团聚体稳定性差异较大，因而母质和土地利用对团聚体稳定性和团聚体有机碳会有重大影响。为此，在湖南省大围山花岗岩发育红壤和小溪国家自然保护区板岩发育红壤小流域，采集典型土地利用和土壤深度（间距20 cm，深度100 cm）土壤样品，采用约瑟法的干筛和湿筛处理、以及Le Bissonnais法的快速湿润、慢速湿润和预湿润3种处理方式测定土壤团聚体稳定性，并测定了团聚体有机碳含量。结果表明，快速湿润对土壤团聚体稳定性破坏最大，而慢速湿润最小，因此快速湿润处理方式下所引起的消散作用是土壤团聚体破碎的主要机制；母质和土地利用对团聚体稳定性具有显著影响，板岩红壤抵抗侵蚀的能力要高于花岗岩红壤，由天然林转化为果园和坡耕地后，土壤团聚体稳定性降低；母质和土地利用也会显著影响团聚体有机碳含量，板岩红壤坡耕地团聚体有机碳含量高于花岗岩红壤，不同土地利用团聚体有机碳含量排序为人工林>坡耕地>天然林>果园；团聚体稳定性对有机碳具有显著性影响，相对消散指数、相对机械破碎指数以及团聚体特征参数均与总有机碳含量呈显著负相关(P <0.05)，而土壤有机碳总量与团聚体平均重量直径、几何平均直径和水稳性团聚体含量之间均存在显著正相关关系(P <0.05)。研究结果对于南方红壤区土壤侵蚀的控制和土壤质量的提升具有重要意义。该项目共计发表论文6篇，其中第一标注SCI论文2篇（一区TOP），第一标注中文2篇，第二标注SCI论文2篇。培养硕士生1名。