Variation and relationship of loess microstructure and soil water characteristic curve under different vegetation covers

The Loess Plateau, a representative arid and semi-arid region, exhibits unique hydrological and soil properties that are critical for ecological restoration and environmental management. Understanding the relationship between loess microstructure and its soil water characteristic curves (SWCC) under different vegetation types is essential for predicting water retention and hydrological behavior. This study utilizes the contact filter paper method, laser particle size analysis, and scanning electron microscopy (SEM) to explore the microstructure and SWCC of loess under different vegetation types, including grassland, shrubland, and arbor cover. The findings reveal that loess under arbor cover exhibits the highest clay content (40.33%), followed by grassland (36.31%) and shrubland (34.18%), and the structural stability is also more extraordinary under arbor cover. In terms of pore structure, loess under arbor cover has the highest average porosity (35.99%), followed by grassland (34.48%) and shrubland (31.69%). In addition, significant variations in SWCC were identified among loess samples under various vegetation types. At the same matric suction, loess under arbor cover exhibited the highest volumetric water content, followed by grassland and shrubland. The influence of loess microstructure on SWCC is mainly reflected in its regulation on the fitting results of soil saturated water content and residual water content. These results suggest that vegetation cover type markedly influences the particle composition, pore structure, and water retention capacity of loess. Comprehensive analysis of the microstructure and SWCC across different vegetation types offers critical insights into soil and water resource dynamics during vegetation restoration on the Loess Plateau.