The role of roots traits of climax community species to shear strength in the Loess Hilly Region, China

the climax community species, especially their roots, have been found very helpful to increase slope stability and reinforce the soil on the Loess Plateau of China. However, the effect of root-soil shear resistance is poorly understood on plant roots mechanical traits and chemical compositions on the Loess Plateau. Thus, this study evaluated the correlations among root mechanical properties, root chemical compositions and root parameters traits, and effects of root traits on soil shear resistance. In this study, the roots of climax community species (Bothriochloa ischaemum (L.) Keng. (B. ischaemum), Carex tristachya Thunb. (C. tristachya), Artemisia gmelinii Web. (A. gmelinii), and Artemisia giraldii Pamp. (A. giraldii)) were subjected to be a series of laboratory tests of biochemical, biomechanical and direct shear strength with different soil layers. The findings of the study revealed that (1) Over 65% of the total measured root parameter traits were distributed in the upper 20 cm of the soil, and they decreased with increasing soil layer. There was the highest Tr by B. ischaemum as a failure (386.5 MPa), followed by C. tristachya (30.97 MPa), A. gmelinii (24.67 MPa), A. giraldii (8.95 MPa). The tensile properties (Tr (root tensile strength) and Tf (tensile force)) were significantly correlated with root diameter. The contents of root lignin were significantly correlated with root diameter while cellulose and hemicellulose showed no obvious trend with root diameter. Tr was significantly positive correlation from cellulose and lignin. (2) The presence of plant roots enhanced the soil cohesion by 13.34~115.05%. The soil cohesion is negatively correlated with the soil layers whether the root-soil composites or the soil without roots. (3) The root-soil composite cohesion can be explained by RSAD (root surface area density), followed by RLD (root length density) and D (root diameter), and the internal friction angle can be explained by Tr, followed by cellulose and lignin. These conclusions were provided theoretical guidance and data accumulation for the mechanical traits, soil reinforcement and slope stability of climax community species roots in the Loess Plateau of China.

Automated summary

This study evaluated the correlations among root mechanical properties, root chemical compositions, and root parameters traits, and the effects of root traits on soil shear resistance in climax community species on the Loess Plateau. The study found that over 65% of the root parameter traits were distributed in the upper 20 cm of the soil and decreased with increasing soil layer. Plant roots enhanced the soil cohesion and the soil cohesion was negatively correlated with the soil layers. The root-soil composite cohesion can be explained by root surface area density (RSAD), root length density (RLD), and root diameter (D). This study provides theoretical guidance and data accumulation for the mechanical traits, soil reinforcement, and slope stability of climax community species roots in the Loess Plateau.