为明确用于三峡库区植被构建的边坡植物物种根系特征与土壤抗剪强度之间的关系，该文以裸地为对照，应用WinRHIZO（Pro.2004c）根系分析系统对香根草（Vetiveria zizanioides(Lin.) Nash）、百喜草（Paspalum notatum Flugge）、狗牙根（Cynodon dactylon(L) Pers.）和紫花苜蓿（Medicago sativa L.）4种护坡草本的根系特征进行定量分析。研究发现：香根草的根长密度和根表面积密度显著大于其他草本；各草本类型的根长密度、根表面积密度及根重密度均随着土壤深度的增加递减，但随深度的增加，不同草本类型的差异逐步缩小；不同草本类型土壤内摩擦角φ和粘聚力c大小均为：香根草＞百喜草＞紫花苜蓿＞狗牙根＞裸地，且随土层深度的增加而降低；随着根长密度、根表面积密度的增大，土壤内摩擦角φ呈显著的对数增长，土壤粘聚力c呈显著的线性增长，且与直径D≤5 mm不同径级的根系特征之间存在明显的相关性。结果表明：相对于裸地而言，4种草本均能显著增强土壤内摩擦角φ和粘聚力c，且根系对土壤内摩擦角φ的提高程度大于土壤粘聚力c；根长密度和根表面积密度，尤其是直径D≤5 mm径级的根长密度和根表面积密度能很好的表征土壤的抗剪强度，可作为评估土壤抗剪强度的重要参数。%Plant root systems play an important role in soil erosion control. To investigate characteristics of root systems of herb vegetation for erosion control in the Three Gorges Reservoir region and their influences on soil shear strength, we used bare land as a control. Four typical herb plants of erosion control, Vetiveria zizanioides (Lin.) Nash, Paspalum notatum Flugge, Cynodon dactylon (L) Pers. and Medicago sativa L., were selected and investigated in the experiments. Circular knives (base area:30 cm2, high:10 cm) were used to take samples from the test area for analysis. Direct shear apparatus was applied to analyze soil shear strength. A root analysis system (WinRHIZOPro.2004c) was used to characterize the root systems. The results indicated that: 1) Vetiveria zizanioides (Lin.) Nash had the largest root length density and root surface area density. 2) Root length density, root surface area density, and root weight density of all typical herb plants were decreased with the increasing of soil depth, but the difference on root length density, root surface area density, and root weight density among different herb plants was not significant with the increasing soil depth. The root length density, root surface area density, and root weight density were 0.92 cm/cm3, 0.29 cm2/cm3, and 2.10 mg/cm3 for Cynodon dactylon (L) Pers., 1.01 cm/cm3, 0.77 cm2/cm3 and 34.72 mg/cm3 for Medicago sativa L., 8.12 cm/cm3, 3.12 cm2/cm3 and 27.70 mg/cm3 for Vetiveria zizanioides (Lin.) Nash and 1.66 cm/cm3, 0.71 cm2/cm3 and 9.26 mg/cm3 for Paspalum notatum Flugge, respectively. 3) Soil shear strength was significantly different in the 4 herb plants. Even in the same herb plant, it had different patterns with the difference of soil layers. The internal friction angleφand cohesion c declined with the increasing of soil depth. We found that the internal friction angle φand cohesion c of all herb plants were higher than that of bare land. The sequence from high to low were: Vetiveria zizanioides (Lin.) Nash>Paspalum notatum Flugg>Medicago sativa L. >Cynodon dactylon (L) Pers. 4) The internal friction angleφ, cohesion c, and shear displacement were 14.79º, 15.96 kPa, and 3.43 mm for Cynodon dactylon (L) Pers., 17.44º, 20.93 kPa and 4.89 mm for Medicago sativa L., 24.04º, 31.36 kPa and 2.88 mm for Vetiveria zizanioides(Lin.) Nash and 18.71º, 30.34 kPa and 3.63 mm for Paspalum notatum Flugge and 9.45º, 14.18 kPa and 5.51 mm for bare land, respectively. 5) The internal friction angleφwas logarithmic growth and cohesion c was linear growth with the increase of root length density and root surface area density, and soil shear strength had an obvious correlation relationship with root systems when the diameter was less than 5 mm. It is concluded that root length density and root surface area density are the best indexes to characterize soil shear strength, especially root length density and root surface area density of roots with D≤5 mm. The results will be useful for hillslope vegetation protection and soil erosion control.
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