黄土高原退耕还草土壤有机-无机碳耦合过程对团聚体稳定性的影响机制

Soil aggregates are structural units within the soil, which plays an important role in the maintenance for soil structure, and affects nutrient cycling and soil erosion. Vegetation restoration is one of the fundamental measures for soil and water conservation and ecological environment construction in Loess Plateau and can improve regional ecological balance through soil-plant system. In the process of vegetation restoration, soil organic matter increases with litter, which leads to the strong interaction between soil organic matter and carbonates in the loess. However, there is limited information about the effect of the interaction mechanism between organic and inorganic carbon on the stability of aggregates. In this project, the soils with grass restoration after conversion of cropland to grassland in the Yunwu Mountain Reserve for Vegetation Protection and the Eco-environment in the city of Guyuan, Ningxia Province on the Chinese Loess Plateau will be sampled. The variances of and the interaction between soil organic matter and carbonates in soil aggregates with the different sizes will be investigated. The effects of interaction mechanism between organic and inorganic carbon on the stability of aggregates will be discussed. This project aims to promote our understanding of the mechanism on the vegetation restoration of degraded soil structure.

团聚体是土壤的基本结构单元，其质量与数量影响着土壤的结构、养分供应以及抗蚀性能。退耕还林（草）是黄土高原地区水土流失治理与生态环境建设的基本措施。在退耕过程中，凋落物等土壤碳源的增加导致土壤有机质含量增大，与黄土中大量的碳酸盐相互作用增强，它们相互作用的过程及其对团聚体稳定性的影响机制并不清楚。因此，本项目以黄土区宁夏固原云雾山退耕还草植被恢复不同年限的土壤为研究对象，以土壤有机碳-无机碳相互作用为核心，研究退耕还草植被恢复过程中有机质与碳酸盐含量的动态变化，分析二者相互作用过程中不同粒径土壤团聚体中胶结物质组成和结构特征，探讨有机碳和无机碳的耦合过程对团聚体稳定性的影响机制。所得结果将为黄土高原生态恢复提供科学指导。

团聚体是土壤的基本结构单元，土壤粘结物质组成的变化将影响其稳定性。本项目以黄土区安塞纸坊沟退耕还草植被恢复不同年限的土壤为研究对象，分析了0-50 cm土层不同土壤胶结剂（有机碳、无机碳和氧化铁）的垂直分布特征，明确了植被恢复过程中全土胶结剂含量的变化特征，探明了胶结剂在团聚体中的分布特征及其对团聚体形成和稳定的贡献。主要结果如下：（1）草地植被恢复促进0-20 cm土层有机碳（SOC）和球囊霉素，以及0-50 cm土层无机碳（SIC）、游离氧化铁（Fed）、无定形氧化铁（Feo）和络合态铁（Fep）含量增加；随土层深度，SOC减小，而SIC和Feo增加。（2）各粒级团聚体SOC和SIC含量随恢复年限呈增加趋势，Fed和Feo呈先增后减趋势。SIC在微团聚体（0.25-0.053 mm）中含量最高，在粉粘粒（< 0.053 mm）最低。（3）土壤团聚体稳定性指数（MWD）随恢复年限呈增加趋势（特别是0-20 cm 土层），随土层深度呈降低趋势。随恢复年限，大团聚体（> 2 mm）含量逐渐增加，而粉粘粒（< 0.053 mm）逐渐降低。（4）0-10 cm和10-20 cm土层胶结物质对团聚体稳定性的总贡献率分别为68.6%（Feo贡献最大）和81.8%（SOC最大），而20-50 cm较低，为23.2%~33.3%。（5）SOC和Feo主要促进> 2 mm粒级团聚体稳定，SIC主要促进0.25-2 mm粒级团聚体稳定。