Effects of biochar on the root morphological and mechanical properties of Lespedeza bicolor Turcz. on slopes in high-altitude areas

To investigate the effects of biochar on the root growth and soil reinforcement capacity of slope vegetation in high-altitude regions, in this study, Yajiang County, Garze Tibetan Autonomous Prefecture, Sichuan Province, was selected as the experimental area, and Lespedeza bicolor was selected as the research object. Six biochar application gradients were established: 0 kg·m-2 (CK), 2.5 kg·m-2 (I), 5 kg·m-2 (II), 7.5 kg·m-2 (III), 10 kg·m-2 (IV), and 12.5 kg·m-2 (V). The effects of different application rates on the soil physical and chemical properties, root morphology, chemical composition, and tensile strength of L. bicolor were systematically analyzed. The results indicated that the biochar application rate significantly affected the root morphological and mechanical properties. Under Treatment III (7.5 kg·m-2), the root length, root biomass, total root length, and specific root length of L. bicolor were significantly greater than those under the other treatments. Moreover, this treatment resulted in the highest tensile strength of the secondary lateral roots, which was accompanied by an increase in cellulose content and a decrease in lignin content. Root tensile strength was positively correlated with cellulose content and negatively correlated with lignin content. In conclusion, an appropriate amount of biochar can promote root development and increase its tensile strength by improving soil conditions and regulating root chemical composition. Among the tested concentrations, 7.5 kg·m-2 was the optimal biochar application rate for enhancing the soil reinforcement capacity of the roots of L. bicolor in this region. This study provides theoretical support and a practical reference for slope ecological restoration in high-altitude areas.