黏质土壤孔隙结构对团聚体稳定性的影响机制

Soil aggregate is the basic unit of soil structure and its stability serves as an indicator of soil fertility, quality and resistance to erosion. Soil structure consists of two phases, the solid phase and the pore phase, both of which influence soil structure stability. Compared with cementing materials, less knowledge is available about the influence of pore structure on aggregate stability and its mechanism. On the basis of soil geography and genesis theories, a series of clayey soils developed in different degrees (Isohumosols, Argosols, Ferrosols, Ferralosols) are selected from the quaternary sediments as experimental objects. Pore characteristics including pore morphology, topology and size distribution are quantitatively analyzed by using the combined methods of X-ray computed tomography, mercury intrusion porosimetry and gas adsorption. The variations of soil pore structure in response to soil type, genetic horizon and aggregate size are investigated separately at the scale of region, soil profile and aggregate. The relationships between aggregate stability with cementing agents and pore structure are evaluated by measuring the aggregate water, chemical and mechanical stabilities in order to reveal the influence mechanism of pore structure on aggregate stability. The obtained results will expand the knowledge of soil structure formation and stabilization mechanisms, provide some novel insights into soil processes and functions, and improve the land management and utilization.

土壤团聚体是土壤结构的基本单元，其稳定性反映了土壤肥力、质量状况及抗侵蚀能力。物质组成和孔隙是土壤结构重要性质，共同影响结构稳定性。然而相比胶结物质，孔隙结构对团聚体稳定性的影响程度及内在机制尚不清楚。本项目拟从土壤地理发生学角度出发，选取第四纪沉积物母质上不同发育程度的黏质土壤（均腐土、淋溶土、富铁土、铁铝土）为研究对象，综合应用X射线断层扫描技术、压汞法和气体吸附法等技术手段，定量分析土壤孔隙的三维结构、形态、数量和空间分布特征，分别从区域、土体剖面和团聚体尺度研究孔隙结构随土壤类型、发生层和团聚体粒径的变化规律；结合团聚体水稳性、力学稳定性和化学稳定性分析，研究团聚体稳定性与胶结物质和孔隙结构的关系，揭示孔隙结构对团聚体稳定性的影响机制。项目的开展有助于完善土壤结构形成和稳定机理、深入理解土壤过程及功能，为土地合理管理利用提供科学依据。

土壤团聚体是土壤结构的基本单元，其稳定性反映了土壤肥力、质量状况及抗侵蚀能力。物质组成和孔隙是土壤结构重要性质，共同影响结构稳定性。然而相比胶结物质，孔隙结构对团聚体稳定性的影响程度及内在机制尚不清楚。本项目在我国东亚季风区自北向南按气候梯度选取第四纪沉积母质发育八种典型地带性土壤（黑土、棕壤、褐土、黄褐土、棕红壤、红壤、赤红壤和砖红壤）为研究对象，系统分析了土壤孔隙结构空间演变特征，综合评价了土壤团聚体水稳性、力学稳定性和化学稳定性，揭示了团聚体稳定破碎机制。主要研究成果有：（1）从物质组成和孔隙结构两方面系统解析了土壤结构的空间分异，发现不同孔隙组分随土壤发育程度呈现不同演变特征，其中基质孔隙主要受无机成土物质影响呈现明显地带性分异，结构性孔隙主要受有机组分影响呈现明显剖面变化，而大孔隙的空间分异特征不明显；（2）从区域、土体和团聚体尺度揭示可团聚体水稳性变化规律及其稳定破碎机制，发现层状硅酸盐黏土矿物主导团聚体水稳性的地带性变化，总孔隙度和基质孔隙体积对团聚体水稳性起促进作用，在土体尺度，有机质对团聚体水稳性发挥重要作用，但其稳定效率随着土壤发育程度增加而降低；提出一种团聚体稳定性测定新方法，用来解析团聚体破碎过程中消散作用和机械震荡作用的单独与耦合效应；（3）团聚体力稳性主要受总孔隙度、结构性孔隙的影响，此外膨胀性矿物-蛭石可以增强团聚体力稳性，而高岭石和铁铝氧化物会降低团聚体力稳性；（4）不同类型土壤团聚体对溶液组成呈现不同破碎响应。对于结构稳定性较差的土壤，溶液组成对团聚体破碎影响不显著；而结构稳定性较好的弱中等发育土壤和强发育土壤，团聚体破碎对电解质溶液组成表现相反的响应行为。上述成果丰富完善了土壤结构形成稳定理论，有助于深入理解土壤过程和功能，同时为土地管理、利用和改良措施优化设计提供了科学依据。