随着黄土高原生态恢复进行到达新的阶段，多年生草植根系的动态生长如何改变浅层土体的强度特征与水力参数，成为地质灾害防控与生态恢复交叉领域亟待深入探索的问题之一。本文在黄土高原典型露天矿开采后的植被恢复试验区，针对多年生豆科-直根型紫花苜蓿与禾本科-须根型植物高羊茅两种典型生态恢复草植，选取人工恢复植被1年、3年和5年的黄土边坡进行根系和根-土复合体的取样，在探明草植根系形态特征与抗拉强度随生长时间演化规律的基础上，研究草植根系生长过程中根-土复合体抗剪强度、饱和渗透与持水能力等关键水、力特性的时变规律，并结合染色示踪与核磁共振试验从根-土孔隙结构演化和优先流入渗的角度讨论草植根系生长对边坡浅层土体的影响。研究内容及主要结论如下：

   （1）随着植物生长年限的增加，根系的总长度、体积和表面积逐年显著增加。特别是紫花苜蓿，根系的扩展能力较强，根长和根体积的增幅明显大于高羊茅。紫花苜蓿根系的总长度从1年生增至5年生根系的生物量和表面积也随年限增加而显著提升。高羊茅的根系虽然增长较慢，但随着年限的延长，其根系在深层土壤中的占比和生物量逐步增加。

   （2）随着草植年限的增长，根系对土壤的固土效果逐渐增强，尤其是紫花苜蓿，根系能够显著提高土体的抗剪强度。对于根-土复合体的渗透性，研究表明紫花苜蓿和高羊茅根系在不同吸力条件下对非饱和渗透性有显著影响。紫花苜蓿根系在低吸力阶段通过根-土通道有效促进水流动，从而提高了土壤的非饱和渗透系数，而在高吸力阶段，根系的导流效应逐渐减弱。相比之下，高羊茅的根系在低吸力阶段对渗透性的改善较为显著，但在高吸力下其作用减弱。

   （3）不同年限的草植根系对土壤水分的优先流特征有显著影响，6个样地中的优先流发育情况为：5年生紫花苜蓿＞3年生紫花苜蓿＞5年生高羊茅＞1年生紫花苜蓿＞3年生高羊茅＞1年生高羊茅。随着植被年限的增长，优先流特征逐渐增强，尤其是紫花苜蓿，水分沿其根系的渗透路径进入土壤的深层，形成较为明显的优先流现象。长期种植的草植根系通过其发达的根系网络，形成了更加有效的水分传导通道，显著提高了土壤的渗透能力，减缓了地表径流的产生，防止了水土流失。

   （4）植物根系的生长年限与土壤水分分布、边坡稳定性及水土保持效应之间存在显著关系。长期种植的草本植物能够有效改善边坡的渗流场，提升边坡的水土保持能力。紫花苜蓿和高羊茅在5年生阶段，特别是在深层土壤中，对水分的调蓄能力明显增强，有助于缓解强降雨时的水土流失问题。

      As the ecological restoration of the Loess Plateau enters a new phase, the impact of the dynamic growth of perennial grass roots on the strength characteristics and hydraulic parameters of shallow soils is one of the issues that requires in-depth exploration at the intersection of geological disaster prevention and control and ecological restoration. This paper focuses on two typical grasses used in ecological restoration: perennial legume-taproot alfalfa and graminoid-furrowed tall fescue. Root systems and root-soil composites were sampled from loess slopes with 1, 3 and 5 years of vegetation restoration to explore the morphological characteristics of the grasses' root systems and the evolution of their tensile strength over time. The sampling was conducted in the experimental area of vegetation restoration after a typical open-pit mine on the Loess Plateau. The time-varying patterns of key hydraulic properties, such as shear strength, saturated infiltration and water-holding capacity, of the root-soil complex were investigated based on the evolution of the morphological characteristics and tensile strength of the root system with growth time. The effects of grass plant root growth on shallow slope soils were also discussed in the context of the evolution of root-soil pore structure and preferential inflow of infiltration by combining staining tracer and nuclear magnetic resonance experiments. The research content and main conclusions are as follows:

   （1）The total length, volume and surface area of the root system increased significantly with each additional year of plant growth. Alfalfa, in particular, had a greater ability to expand its root system; the increase in root length and volume was significantly greater than that observed in tall fescue. The total length of the alfalfa root system increased from one year old to five years old, and the biomass and surface area of the root system also increased significantly over time. Although growing more slowly, the root system of tall fescue gradually increased its percentage and biomass in the deep soil with each passing year.

      (2) As the number of years of grass planting increased, the effect of the root system on soil consolidation gradually increased, particularly in the case of alfalfa, where the root system was able to significantly increase the shear strength of the soil. Regarding the permeability of the root-soil complex, the root systems of alfalfa and tall fescue were found to significantly affect the unsaturated permeability under different suction conditions. At low suction stages, the alfalfa root system effectively promoted water flow through the root-soil channels, thus increasing the soil's unsaturated permeability coefficient. However, at high suction stages, the root system's conductive effect gradually weakened. Conversely, tall fescue roots improved permeability more significantly at low suction, but their effect weakened at high suction.

      (3) The root systems of grass plants of different ages significantly affected the preferential flow characteristics of soil moisture. The development of preferential flow in the six sample plots was as follows: Five-year-old alfalfa > three-year-old alfalfa > five-year-old tall fescue > one-year-old alfalfa > three-year-old tall fescue > one-year-old tall fescue. As vegetation age increased, preferential flow characteristics gradually increased, particularly in alfalfa. Here, water entered the deeper soil layers along the infiltration path of the root system, forming a more obvious preferential flow phenomenon. The root systems of long-term grass plantations formed more effective water conduction channels through their well-developed networks, significantly improving the infiltration capacity of the soil, slowing down the generation of surface runoff and preventing soil erosion.

      (4) There is a significant relationship between the growth period of plant roots, soil moisture distribution and slope stability, as well as the effect on soil and water conservation. The long-term planting of herbaceous plants can effectively improve the seepage capacity of slopes and enhance their soil and water conservation ability. Alfalfa and tall fescue significantly increase water storage capacity after five years, particularly in deep soil, helping to alleviate soil erosion problems during heavy rainfall.

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