Herbaceous root architecture and mechanical traits underpin terrace wall reinforcement: A nature-based solution for sustaining mountain agriculture

• Root architecture directly and indirectly enhanced the stability of the terrace wall. • Fine roots (diameter < 0.9 mm) predominantly contributed to root tensile strength. • High soil moisture content significantly reduced terrace wall stability. Terrace wall stability is crucial for agricultural sustainability in mountainous regions worldwide. While herbaceous root reinforcement offers a sustainable alternative to conventional engineering-based fortifications, the mechanistic links between specific root traits and their stabilization efficiency remain insufficiently understood. Here, we investigated the architectural and mechanical properties of three herbaceous species root systems ( Alopecurus aequalis , Hedyotis chrysotricha , and Dicranopteris dichotoma ) and assessed their effectiveness in enhancing soil shear strength, thereby reinforcing terrace wall stability. Our results revealed a hierarchical soil shear strength enhancement of bare soil (16.73 kPa) < A. aequalis (28.83 kPa) < H. chrysotricha (42.53 kPa) < D. dichotoma (55.58 kPa), with the highest stabilization efficiency for D. dichotoma , 232.32% higher than bare soil in soil shear strength. Terrace wall stability was significantly influenced by root architecture (with path coefficient β = 0.56, p < 0.01), root additional cohesion ( C R ) (β = 0.29, p < 0.05), soil aggregate stability (MWD) (β = 0.24, p < 0.05), and soil moisture content (β = -0.37, p < 0.01). Specifically, topological index (with factor loading λ = 0.95) and fractal dimension (λ = 0.94) were key contributors to root architecture, which emerged as the primary stabilizer for terrace walls. Beyond its direct effect, root architecture also exerted indirect effects by significantly improving the soil aggregates stability (MWD) (β = 0.58, p < 0.001) and root additional cohesion ( C R ) (β = 0.78, p < 0.001). Our findings identify four essential strategies for stabilizing terrace walls, with broad applicability to analogous mountainous agricultural systems globally: (i) selecting species with a high topological index (TI) (e.g., D. dichotoma , TI = 0.95) to enhance root-soil interlocking, (ii) promoting fine roots under 0.9 mm diameter to increase tensile strength, (iii) implementing effective drainage systems to mitigate moisture-induced destabilization, and (iv) preserving soil aggregate stability.