Effects of mineral-solubilizing microbial strains on the mechanical responses of roots and root-reinforced soil in external-soil spray seeding substrate.

There are a large number of abandoned mining areas in China, where external-soil spray seeding is a common technique used to assist with the restoration of these areas. However, the soil component of external-soil spray seeding is deficient, and they are prone to collapse, which complicates ecological restoration. In this study, we added a mineral-solubilizing microbial strain to an external-soil spray seeding substrate in Robinia pseudoacacia and Lespedeza bicolor pots, which were monitored from December 2018 to November 2019. We investigated their root growth and root tensile properties, as well as root-reinforced soil shear strength. The results revealed that the addition of the microbial strain in the substrate improved root growth of Robinia pseudoacacia. The root-reinforced soil shear strength, tensile force and strength were also strengthened by the added microbial strain. Although the growth rate of Robinia pseudoacacia was faster than that of Lespedeza bicolor, the shear strength of the root-reinforced Robinia pseudoacacia soil was lower than that of the Lespedeza bicolor root-reinforced soil of the same diameter. Finally, compared with the cohesion, the change in the friction angle is relatively small, and differences in cohesion resulted in shear strength changes under the same treatment. Our results suggested that the addition of a mineral-solubilizing microbial strain to the external-soil spray seeding substrate could help plants strengthen the soil and positively enhance its effects. These results might also enrich the existing data on the effects of mineral-solubilizing microbial strains on plant roots, while guiding further studies toward improving the efficacy of external-soil spray seeding technologies.