Altitudinal patterns of particle size distribution and Atterberg limits in subtropical soil profiles of South China

Soil particle size distribution (PSD) and Atterberg limits are critical indicators reflecting soil structural stability and plasticity. Clarifying their altitudinal and vertical differentiation patterns and coupling mechanisms is essential for revealing the hydrological and ecological functions of mountain soils regarding water retention and erosion resistance. However, the gradient differentiation of soil particle structure and plastic properties remains poorly understood in subtropical mountainous regions. In this study, soil profiles across seven altitude gradients were investigated to explore the altitudinal and vertical variations in PSD, fractal dimensions, and Atterberg limits, and further reveal the regulatory effects of particle structure on soil plastic properties. The results showed that mountain soils in the study area were dominated by silt particles with the lowest clay content. Clay content and monofractal dimension exhibited unimodal variations with altitude and soil depth. Multifractal characteristics could precisely characterize the heterogeneity of soil particle composition. Atterberg limits show significant altitudinal differentiation ( p < 0.05) with a unimodal trend primarily controlled by clay content. Driven by topsoil organic matter accumulation and clay eluviation‐illuviation, Atterberg limits peak in topsoil and illuvial horizons. Moreover, significant coupling relationships existed between Atterberg limits, particle composition, and multifractal parameters, indicating that particle structure serves as a core factor regulating the vertical and altitudinal differentiation of mountain soil physical properties. This study adopts multifractal analysis to quantify altitude‐dependent PSD variation and clarify the particle‐regulated spatial heterogeneity of soil plasticity, providing theoretical insights into soil and water conservation in subtropical mountainous regions.