西宁盆地黄土区草本和灌木组合根系分布特征及其增强土体抗剪强度效应

为了研究草本和灌木组合种植条件下根系的护坡力学效应,本试验以种植于西宁盆地自建试验区生长期为1 a的6种草本和灌木组合作为试验供试种,在草本和灌木组合根-土复合体原状试样直剪试验基础上,评价了6种组合根系分布特征及其对边坡土体抗剪强度的增强效应。试验结果表明:试验区6种草本和灌木组合根系主要分布在边坡地表以下0~30 cm深度范围内,含根量随着取样深度增加呈线性函数或指数函数降低趋势;6种组合草本与灌木根系质量比随着土体深度增加,呈先降低后增大的变化趋势,且两者间符合二次函数关系;6种草本和灌木组合根-土复合体黏聚力在边坡地表以下0~30 cm深度范围内,较素土黏聚力增幅为2.47%~70.96%,说明草本和灌木组合根系能够起到增强边坡土体黏聚力的作用,其中组合5(紫花苜蓿+垂穗披碱草+碱茅+草地早熟禾+柠条锦鸡儿)对边坡土体黏聚力的增强作用相对较为显著。上述试验成果对于西宁盆地及其周边地区生态恢复和植被护坡工程实施具有一定的实际指导意义和理论研究价值。

DISTRIBUTION CHARACTERISTICS OF COMBINED HERB AND SHRUB ROOTS IN LOESS AREA OF XINING BASIN AND THEIR EFFECT ON ENHANCING SOIL SHEAR STRENGTH

This paper investigates the slope protection effect by vegetation and its mechanical role in increasing soil strength. It chooses six types of combinations of herbs and shrubs with their growing period of 1 a as the tested species. Built on these, the undisturbed root-soil composite systems of six types of vegetation combinations received direct shear tests to evaluate their contribution in increasing soil strength and to analysis their roots distribution characteristics. The results exhibit that for the six types of vegetation combinations, most of their roots distribute in a range of 0 to 30 cm beneath the ground surface, with their roots distribution type exhibiting a linear or exponential declining trend. The mass ratio of herb roots to shrub roots exhibit an initial decreasing and then increasing trend with soil depth increasing, which can be described with a quadratic function. In the depth of 0 to 30 cm beneath the ground surface, the cohesion of the root-soil composite systems of six types of vegetation combinations increases by 2.47% ~70.96%, comparing with that of soil without roots. The result indicates the roots of the six types of vegetation combinations exerts a significant role in increasing soil cohesion. Of these vegetation combinations, the vegetation combination of Medicago sativa L.+ Elymus nutans Griseb.+ Puccinellia distanx(L.)+ Poa pratensis L.+ Caragana korshinskii Kom exerts a dominant role in increasing soil cohesion compared to other vegetation combinations. The results of this study have practical guiding significance and theoretical research value for the ecological restoration and vegetation slope protection project in Xining Basin and its surrounding areas.