关键词: 地表径流, 植被盖度, 降雨强度, 土壤理化性质, 黑麦草, 根系参数, 黄土高原

Abstract:

【Objective】Grass cover plays a critical ecological role in regulating slope runoff during rainfall. However, quantitative studies on how root systems and soil properties change during grass cover restoration and subsequently affect slope runoff remain limited.【Method】In this study, indoor simulated rainfall experiments were conducted to systematically examine the effects of varying rainfall intensities (40, 80, and 120 mm·h^-1) and grass cover levels (0%, 33%, 48%, 56%, and 69%) on surface runoff characteristics, soil physicochemical properties, root parameters, and their combined influence on slope runoff in ryegrass (Lolium perenne) plots (2 m×0.5 m×0.4 m, 15° slope).【Result】(1) Compared with bare slopes, grass cover restoration significantly improved the physicochemical properties of the surface soil (0-10 cm). Specifically, it led to a 2.4% decrease in soil bulk density and increases of 1.4%, 9.4%, 227.1% and 82.5% in total soil porosity, mean weight diameter of aggregates, saturated hydraulic conductivity, and soil organic matter content, respectively, with all improvements enhanced by increasing cover. Meanwhile, root parameters (root length density, root surface area density, and root volume density) of grass plots increased significantly with increasing cover. Regression analysis further indicated that grass root growth directly drove corresponding changes in topsoil properties, and the improvement in soil saturated hydraulic conductivity was the most significant. (2) Under the same rainfall intensity, the initial runoff time increased significantly with greater grass cover, while the average runoff rate decreased, with runoff reduction benefits increasing accordingly (7.7%, 13.3%, 16.9%, and 27.1%). With increasing rainfall intensity, the initial runoff time was markedly shortened, and the greater the grass coverage, the larger the reduction magnitude. Meanwhile, the average runoff rate rose significantly, accompanied by a decline in corresponding runoff reduction benefits (24.7%, 15.9%, and 8.1%); moreover, the weakening trend of the regulatory effect of grass cover on slope runoff with increasing rainfall intensity was particularly obvious at higher coverages (56% and 69%). (3) The changes in plant roots and soil physicochemical properties during grass restoration significantly influenced slope runoff processes. Path model analysis indicated that the direct effect of plant roots on runoff rate (standardized path coefficient: -0.60) was greater than the indirect effect (standardized path coefficient: -0.27). This was attributed to the fact that the increase in grass cover after restoration mainly regulates slope runoff through the physical barrier effect (direct effect) formed by root density, while its indirect effect was primarily achieved by improving topsoil hydro-physical properties and ultimately increasing soil saturated hydraulic conductivity, thereby enhancing water infiltration capacity.【Conclusion】This study revealed the regulatory effect of grass restoration on slope runoff processed by driving changes in topsoil properties through root growth, and this effect was the most significant under high grass coverage. These results provide a scientific basis for erosion control, grassland restoration, and management in the Loess Plateau region.

Key words: surface runoff, vegetation coverage, rainfall intensity, soil physico-chemical properties, ryegrass (Lolium perenne), root parameters, the Loess Plateau