Impact of root diameter, length, and moisture content on the mechanical properties of root systems and the associated implications for ecological slope protection

• Impact of the root diameter, length, and moisture content on the mechanical properties of root systems was examined. • Tensile force of a single root correlates positively with diameter, whereas tensile strength correlates negatively. • Average tensile strengths of natural and soaked roots decrease as root length increases, but dry roots do not obey the law. • Average tensile strength of the roots increases as the root moisture content decreases. • Impact of the root diameter on indoor single root tensile strength exceeds that of the root length and moisture content. Despite the importance of vegetation root systems in soil stabilization and slope protection, the extent to which various factors influence root strength remains unclear. Taking Elsholtzia ciliata , a common plant in the Reshui River small watershed, Xide County, Liangshan Yi Autonomous Prefecture, Sichuan Province, China, as the research object, root tensile tests were firstly conducted to obtain the mechanical properties of the roots, then the effects of the root diameter, length, and moisture content on the indoor single root tensile mechanical properties of Elsholtzia ciliata were analysed, and finally the correlations between them were investigated through grey correlation analysis. The following results were obtained: there is a positive correlation between the indoor single root tensile force of Elsholtzia ciliata and the root diameter, and a negative correlation between the single root tensile strength and root diameter; the average tensile strength of natural and soaked roots of Elsholtzia ciliata decreases with increasing length; the average tensile strength of Elsholtzia ciliata root increases with decreasing moisture content within the tested range; the correlation degrees between the indoor single root tensile force and root diameter, length, and moisture content of Elsholtzia ciliata are 0.895, 0.803 and 0.757, respectively. This implies that the root diameter is the most important factor affecting the indoor tensile force of Elsholtzia ciliata . Thus, when considering vegetation slope protection, selecting vegetation with a large root diameter should be prioritized. These research findings provide valuable references for the future study of ecological slope protection as well as soil and water conservation in small watersheds in mountainous areas.