护坡木本植物根系的力学特性及其与细胞壁成分的关系

Relationship between root mechanical characteristics and cell wall components of woody plant species

为研究人工边坡立地条件下木本植物根系固土护坡的力学机制,以京承高速（3期）边坡为例,对榆树、紫穗槐、刺槐、胡枝子4种木本植物共395个根样进行室内单根拉伸试验,然后按5个根系径级分类并分别测定其半纤维素、纤维素、木质素含量,系统分析植物根系材料的力学性能。结果表明：4种木本植物根系直径为0.95~5.42mm,抗拉强度为7.66~36.94 MPa,抗拉力为22.18~464.50 N。4种植物之间抗拉力、抗拉强度差异显著,从大到小依次为榆树〉紫穗槐〉胡枝子〉刺槐,根系抗拉力随根系直径增大以幂函数增大,抗拉强度随根系直径增大以逆函数或幂函数减小。4种木本植物5个径级根系半纤维素质量分数为1.37%~29.26%,纤维素质量分数为20.57%~36.91%,木质素质量分数为15.12%~29.84%,综纤维素质量分数为28.18%~66.17%,木纤比比值为0.45~1.31。不同树种间及不同径级根系间细胞壁成分差异显著。根系抗拉力与木质素显著负相关;抗拉强度与木质素正相关,与半纤维素负相关。根系拉伸的应力-应变曲线随树种根系结构组成的不同而不同。单根拉伸的应力-应变特征初始阶段为线性关系,拉力继续增大会逐渐表现出塑性特征,根系最大应力随直径增大而减小。综合4种植物的抗拉特性,榆树和紫穗槐的护坡作用较大。

In order to research the mechanical characteristics of artificial slope protection by woody plants,the single root tensile tests were conducted indoors to study these properties of Ulmus pumila,Amorpha fruticosa,Robinia pseudoacacia and Lespedeza bicolor with 395 samples in Jing-cheng（ Ⅲ） expressway where man-made slope was taken as an example. The contents of cell wall components of woody plants were determined such as hemi-cellulose,cellulose,lignin and holo-cellulose after classified into five root diameter classes,and then their mechanical properties were investigated by a systematic analysis. The results showed that a significant difference in tensile force and tensile strength existed between the four woody plants,in descending order as Ulmus pumila,Amorpha fruticosa,Robinia pseudoacacia and Lespedeza bicolor. The root tensile force varied from 22. 18 to 464. 50 N and tensile strength was in the range of 7. 66- 36. 94 MPa with diameters of 0. 95- 5. 42 mm. The root tensile force increased in power function with the increasing root diameter,meanwhile,the root tensile strength decreased in power function and inverse function with the increasing root diameter. The cellulose contents varied from20. 57% to 36. 91%,the lignin contents from 15. 12% to 29. 84%,the hemi-cellulose contents from1. 37% to 29. 26%,the holo-cellulose contents from 28. 18% to 66. 17%,and the content ratio of lignin to cellulose from 0. 45 to 1. 31. The cell wall components showed significant differences between different species and different diameters of root. The root tensile force was negatively correlated with lignin; theroot tensile strength was positively correlated with lignin,but negatively correlated with hemi-cellulose.The results revealed that various root structures have different tensile stress-strain curves. The stressstrain characteristics of the single root presented straight line relation in the initial phase after tension.When the tensile force kept increasing after loading over elastic restrict,the stress-strain curves presented plastic characteristics gradually. According to the root cell wall components and root tensile properties,Ulmus pumila and Amorpha fruticosa had better performance in slope protection in the Jing-cheng expressway（ Ⅲ）.