防风固沙灌木花棒沙柳根系生物力学特性

为了揭示花棒和沙柳的根系生物力学特性,该文选取毛乌苏沙地5 a生人工种植花棒、沙柳的根系为研究对象,通过室内单根拉伸试验,得到沙柳(直径0.78~7.44 mm)的平均最大拉力、抗拉强度和杨氏模量分别比花棒(直径0.91~6.46 mm)高42.07%、44.52%和90.00%。花棒、沙柳单根根系的最大拉力随直径增大以幂函数增大,抗拉强度和杨氏模量随直径增大以幂函数减小。花棒与沙柳单根根系的平均抗拉强度能达到Ⅰ级钢筋(370MPa)的6.86%和9.91%,对土壤有一定的加筋作用。采用自制根系拉力测试系统进行野外原位整株根系垂直拉拔试验,得到花棒(地径17.65~42.68 mm)和沙柳(地径20.35~48.07 mm)的整株根系最大垂直拉拔力为(1.71±0.16)k N和(1.18±0.16)k N,花棒比沙柳高出44.92%。花棒整株根系的生物力学特性要优于沙柳,整体固沙能力更强。该研究可为根系固土作用理论研究和防风固沙树种的筛选提供参考。

Biomechanical characteristics of root systems of Hedysarum scoparium and Salix psammophila

Abstract: Hedysarum scoparium and Salix psammophila play an important role to contribute to sandy soil conservation in Mu Us Desert. In order to reveal the biomechanical properties of these two common shrub species, 5-years-old plant specimens were collected in the Gaoshawo forest field (northwest China) by in situ excavation. The root biomechanical characteristics of Hedysarum scoparium and Salix psammophila were measured by laboratory tensile tests and in situ uprooting tests. To analyze data from those experiments, we used regression and ANCOVA (analysis of covariance) to determine the relationship between roots biomechanical characteristics and root diameter or basal diameter. Results showed that a significant power and linear relationship existed between biomechanical characteristics and root diameter or basal diameter in the two species. The root maximum tension increased with root diameter but tensile strength and Young's modulus increased with decreasing root diameter according to a power function. The maximum uprooting force increased linearly with basal root diameter. The root maximum tension of Hedysarum scoparium was (0.16±0.01) kN (diameter from 0.91-6.46 mm) and Salix psammophila was (0.23±0.01) kN (diameter from 0.78-7.44 mm). The tensile strength of Hedysarum scoparium was (25.38±0.90) MPa and Salix psammophila was (36.68±1.18) MPa. Young's modulus of Hedysarum scoparium was (0.10±0.01) GPa and Salix psammophila was (0.19±0.01) GPa. The tensile strength of two species can reach 6.86% and 9.91% of the first grade steel (370 MPa). It showed that roots had obvious reinforcement function. Roots specimens for each species were tested for the maximum uprooting force measurement. The results showed that the maximum uprooting force of Hedysarum scoparium was (1.71±0.16) kN (basal diameter from 17.65-42.68 mm) and Salix psammophila was (1.18±0.16) kN (basal diameter from 20.35-48.07 mm). Results of ANCOVA using root diameter or basal diameter as a covariate showed that there was significant difference in the root maximum tension (P<0.001), tensile strength (P<0.001), Young's modulus (P<0.001) and roots maximum uprooting force (P<0.05) between two species. Compared to two species, Salix psammophila roots had better biomechanical characteristics in aspect of root maximum tension, tensile strength and Young's modulus. But results of root maximum uprooting force showed that Hedysarum scoparium roots had a better comprehensive biomechanical characteristics than Salix psammophil and hence an better root reinforcement. The maximum uprooting force of Hedysarum scoparium roots was 44.92% higher (0.53 kN) than that of Salix psammophila in the same basal diameter. However, the biomechanical characteristics of single root can not be used as the judgment for root reinforcement ability of the whole tree. The results of this research can serve as a basis for the further studies on biomechanical characteristics of roots and root reinforcement.