Interspecific interactions enhance soil resistance to erosion: Synergistic effects of mixed grass species under simulated rainfall

Mixed seeding of herbaceous plants was frequently employed as a potential ecological restoration strategy in practical applications. However, the effects of mixed grass species to rainfall-induced soil erosion has rarely been evaluated. This study investigated the effects of single and mixed seeding of Lolium perenne and Cynodon dactylon on overland flow and soil loss under varying rainfall intensities through simulated rainfall experiments. The results demonstrated that mixed seeding significantly enhanced aboveground traits, with leaf area index increasing by 67.86 % compared to C. dactylon monocultures and 11.46 % compared to L. perenne monocultures. Belowground traits showed even greater improvements, with root biomass increasing by 80.13 % (vs. C. dactylon) and 59.66 % (vs. L. perenne), root length density by 68.14 % and 29.42 %, and root mass density by 79.81 % and 59.83 %, respectively. Mixed seeding demonstrated superior soil detachment reduction under all rainfall intensities, with soil detachment reductions ranging from 57.86 % to 92.91 %. The contribution of interspecific interactions under mixed seeding is particularly pronounced during intense rainfall, with relative contributions to runoff and soil detachment reduction reaching up to 29.39 % and 21.90 %, respectively. The presence of vegetation significantly altered hydrodynamic parameters to mitigate erosion. Mixed seeding decreased stream power by 19.66 % to 71.35 %, and enhanced the Darcy–Weisbach friction coefficient by a factor of 1.33 ∼ 3.29 relative to single-seeding. Soil detachment rates exhibited a linear relationship with runoff shear stress and stream power. Mixed seeding enhanced soil resistance to erosion by reducing soil erodibility by 30.57 ∼ 44.06 % and critical stream power by 7.59 ∼ 21.18 %, while increasing critical shear stress by 5.68 ∼ 9.41 % compared to monocultures. Furthermore, soil detachment rates exhibited a negative exponential relationship with both aboveground and belowground traits, with the increased traits induced by mixed seeding leading to reduced soil detachment rates. This study provides an in-depth understanding of the erosion control mechanisms of mixed seeding under different rainfall intensities, offering scientific guidance for vegetation configuration on slopes.