Root Tensile Functional Traits of Dominant Herbaceous Species and Their Effects on Soil Shear Strength in the Three Gorges Reservoir Drawdown Zone

Root functional traits are critical predictors for vegetation-mediated slope stabilization in reservoir drawdown zones. This study quantified the biomechanical linkage between single-root tensile traits and macro-scale soil shear strength for three dominant herbaceous species (Cynodon dactylon, Digitaria sanguinalis, and Imperata cylindrica) in the Three Gorges Reservoir. Single-root tests (n=15) revealed a robust diameter-dependent trade-off between tensile load capacity (Fmax) and material efficiency (σt). Direct shear tests on undisturbed root–soil composites demonstrated that root reinforcement significantly enhanced soil stability, primarily by increasing apparent cohesion (c) rather than internal friction. Cynodon dactylon exhibited the highest reinforcement efficacy, increasing cohesion by >50 kPa compared to root-free soil, supported by its superior tensile strength. These findings establish a trait-based mechanistic framework for species selection, suggesting that prioritizing species with high intrinsic tensile efficiency can effectively mitigate shallow erosion under fluctuating hydrological conditions.