运用同步辐射显微CT揭示红壤团聚体内孔隙形态与空间分布

团聚体内部复杂的孔隙系统及其空间分布决定土壤团聚体的主要功能，以及发生在团聚体内的各种物理、化学和生物学过程。应用同步辐射X射线显微成像技术(SR-mCT)，对第四纪红土发育的红壤团聚体内部孔隙形态、连通性、各向异性、大小分布和空间分布进行了研究。结果表明，红壤团聚体内部的孔隙形态、孔隙生长方向、大小分布存在明显差异。稳定性较好的团聚体表现为团聚体孔隙含有较多大孔隙、孔隙形态各异、各向异性、多联通孔隙等特征，团聚体内>30 ?m大孔隙分布比较均匀，中心部位较高，呈中间向圆周减小趋势；反之，稳定性较差的团聚体中，孔隙以小孔隙为主，分布密集，孔隙生长方向均匀，团聚体孔隙空间分布为大孔隙，主要分布在团聚体外围，中心部分分布较少。团聚体内部孔隙的空间分布模式能够很好地解释土壤团聚体结构和稳定性差异的原因。同步辐射显微CT结合图像处理技术能够系统地表征团聚体内孔隙的多样性和空间变异规律，为预测土壤团聚体中各种物理过程提供新途径。

Synchrotron-based X-ray Tomographic Microscopy Reveals Morphology and Spatial Structure of Intra-aggregate Pores in Red Soils

Objective] The pore structure and spatial distribution of intra-aggregates in soils determine many functions of soil aggregates and physical, chemical, and biological processes occurring in aggregate. The objectives of this study were (i) to examine the three dimension (3D) pore characteristics of intra-aggregate pores; (ii) describe the spatial distribution of macropores (>30 ?m) within aggregates, and (iii) to analyze the relation between pore structure and functions of the aggregates. Method] The 3-5 ?m aggregate of two red soils (named as Q4 and Q12) with different stability were used in this study. Synchrotron radiation X-ray microcomputed tomography (SR-mCT) was used to scan the 3-5 mm aggregate of two red soils. A combination of SR-mCT and image analysis was applied to describe the intra-aggregate pore characteristics and pore spatial distribution within the aggregates. Result] The SR-mCT images of aggregates indicated a considerable difference in the morphology, pore size, and pore growth direction of intra-aggregate in two soil samples. The soil Q4 was characterized by abundance macropores, multifarious pore growth direction and pore size distribution, whereas soil Q12 by dense micropores, and consistent pore grow direction. They have similar single pore shape, while different interconnected pore shape. The porosities of 5-30, 50-80, and >80 ?m in soil Q4 were significantly higher than those of soil Q12. The abundance of macropores (>30 ?m) within soil Q4 aggregates was relatively larger in the center part of aggregate, while soil Q12 had a uniform spatial pattern with larger in the outer part of aggregate. Conclusion] The SR-mCT system could clearly describe pore diversity and spatial variation of intra-aggregates without disrupting the aggregate microstructure, which could be effectively to predict the function and physical processes of the aggregates.