黄土区3种优势灌木根土复合体的抗剪强度研究

黄土区水土流失严重,生态护坡是比较推崇的防护手段,特别是灌木具有发达的根系,对含根土体有较为明显的抗剪增强作用,因此,比较自然条件下区域适生优势灌木的根土复合体抗剪强度,对于合理选择固土护坡植物具有重要意义。以黄土区常见的优势乡土灌木达乌里胡枝子(Lespedeza davurica)、中国沙棘(Hippophae rhamnoides)和狼牙刺(Sophora viciifolia)为研究对象,野外采用三维土柱挖取灌木的根系,进行不同直径单根抗拉试验和根土复合体的剪切试验。结果表明:(1)达乌里胡枝子、沙棘和狼牙刺的根系集中分布于0—40 cm土层中,它们的根长密度、根表面积密度和生物量密度随着土层深度的增加表现出整体递减的趋势。(2)达乌里胡枝子、沙棘和狼牙刺根系的抗拉力(Tensile Resistance,TR)与抗拉强度(Tensile Strength,TS)都表现为关于直径(D)的幂函数(aD^b),其中抗拉力与根径呈正相关(b>1),而抗拉强度与根径呈负相关(b<1)。(3)不同灌木根土复合体的抗剪强度在地下分布是不同的,在根际范围内随土层加深,达乌里胡枝子根土复合体的抗剪强度表现出先增加后减少而后增加又减少的趋势,最大抗剪强度的土层是20—30 cm和50—70 cm,沙棘和狼牙刺根土复合体的抗剪强度表现出先增加后减少的趋势,最大抗剪强度的土层分别是30—50 cm,0—20 cm。说明灌木的细根可以更好地起到固土护坡的作用,建议在黄土区优先选择达乌里胡枝子和沙棘作为护坡植物,从而为生态护坡提供一些参考。

Research on Shear Strengths of Root-Soil Complexes of Three Dominant Shrubs in Loess Region

Soil erosion in the loess region is serious.Ecological slope protection is a more respected protection method.In particular,shrubs have a developed root system and have obvious shear resistance enhancement to the soil with roots.Therefore,comparing the shear strengths of the root-soil complexes of the regionally suitable dominant shrubs under natural conditions is of great significance for the rational selection of soil-fixing and slope-protecting plants.We took three dominant native shrubs in Loess Region,Lespedeza dahurica,Hippophae rhamnoides and Sophora viciifolia as the research samples,tensile test of single roots with different diameters and shearing test of root-soil columns were conducted.The results showed that:(1)the root systems of Lespedeza dahurica,Hippophae rhamnoides and Sophora viciifolia mainly distributed in the 0—40 cm soil layer;their root length densities,root surface area densities and biomass densities showed overall decrease with the increase of soil depth;(2)the tensile resistances(TR)and tensile strengths(TS)of Lespedeza dahurica,Hippophae rhamnoides and Sophora viciifolia had the power function(aD^b)relations with the diameters(D),the tensile strength was positively correlated with the diameter(b>1),while the tensile strength was negatively correlated with the diameter(b<1);(3)the shear strengths of different shrubs root-soil complexes were different in the underground distribution;in the rhizosphere,the shear strength of Lespedeza dahurica root-soil complex showed a trend of first increasing,then decreasing,then increasing and decreasing with the increase of soil layer;the maximum shear strength was found in 20—30 cm and 50—70 cm soil layers;the shear strengths of root-soil complexes of Hippophae rhamnoides and Sophora viciifolia showed a trend of first increasing and then decreasing,the maximum shear strength was found in 30—50 cm and 0—20 cm soil layers,respectively.It can be seen that the fine roots of shrubs can better play the roles in soil consolidation and slope protection.It is suggested that Lespedeza davurica and Hippophae rhamnoides should be preferentially selected as slope protection plants in the loess area,so as to provide some references for ecological slope protection.