| The rapid development of China's economy had greatly increased the demand for energy and mineral resources,and the overexploitation of rock mineral resources had led to the abandon of mining areas.In the process of mining,the ecological balance of the mining area had been seriously damaged,resulted in soil erosion,vegetation decline,rock exposure,productivity decline and other harsh ecological environment.External-soil spray seeding technology had been widely used to recover these abandoned mining areas,but external-soil spray seeding substrate was very thin,and it was easy to collapse when the external environment changed.Therefore,a key toward resolving these issues might be to strengthen the soil on the surfaces of rocks,facilitate the long term maintenance and ecological recovery of abandoned mining areas through external-soil spray seeding.Many studies were shown that the ability of the root system to strengthen soil is very important,so it was particularly important to enhance the ability of the root system to strengthen soil.Soil water content could also significantly affect the ability to strengthen soil.In my previous study,microbial strains screened from limestone promoted plant growth.Therefore,it was particularly important to understand the mechanism of the effects of the addition of mineralsolubilizing microbial strains and water retaining agents on soil and plants.Robinia pseudoacacia and Lespedeza bicolor were used in external-soil spray seeding substrate,and four microbial strains treatments(CK,NL-11,NL-11+NL-15 and NL-1+NL-11+NL-15)and three water retaining agents treatments(CK,3‰,5‰)were applied in this experiment to investigate the effects of mineral-solubilizing microbial strains and water retaining agents on the mechanical responses of roots and root-reinforced soils.The results of this study will be likely to enrich existing data on the effects of mineral-solubilizing microbial strains on plant roots,while guiding further studies toward enhancing the efficacy and benefits of external-soil spray seeding technologies.The results were followed:(1)The addition of microbial strains did not significantly change the pH of soil when water retaining agent was not added.When water retention agent was added,the addition of microbial strains affected the pH of rhizosphere soil of Robinia pseudoacacia and Lespedeza bicolor.The addition of microbial strains increased the soil TC,TN and TS,among which double microbial strains have the greatest influence on soil nutrients.The effect of 3‰ water retaining agent on soil TC,TN and TS was greater than that of 5‰ water retaining agent.The addition of microbial strains could increase catalase and sucrase activity in soil.3‰ water retaining agent had the greatest effect on soil enzyme activity.(2)The addition of microbial strains could improve the growth of roots of Robinia pseudoacacia and Lespedeza bicolor,among which the double microbial treatment had the best effect on the growth of root length,root surface area and root volume of Robinia pseudoacacia and Lespedeza bicolor.For Robinia pseudoacacia,under the treatment of SJ,DJ and NJ,the higher the content of water retaining agent,the higher the root length,root surface area and root volume.For Lespedeza bicolor,the improvement effect of 3‰ water retaining agent concentration on root length,root surface area and root volume was higher than that of 5‰ water retaining agent.The growth rate of Robinia pseudoacacia was faster than that of Lespedeza bicolor,but the lignin of the root of Lespedeza bicolor was higher than that of Robinia pseudoacacia.The addition of microbial strains could also increase the content of lignin and decrease the content of cellulose.The addition of water retaining agent decreased the content of lignin and hemicellulose.(3)The addition of microbial strains enhanced the tensile force and tensile strength of roots of Robinia pseudoacacia and Lespedeza bicolor.Under the background of different concentrations of water-retaining agents,the tensile properties of the roots of Robinia pseudoacacia and Lespedeza bicolor were different with the addition of microbial strains.In the case of Robinia pseudoacacia,the effect of the addition of microbial strains on the tensile properties of the root in descending order was as follows: DJ,WJ,SJ and NJ.In the context of 3‰ and 5‰ water retention agent treatment,the effects of microbial strains addition on root tensile properties were listed as follows in descending order: DJ,SJ,WJ and NJ.In the case of Lespedeza bicolor,the effect of microbial strains addition on the tensile properties of the root in descending order was as follows: SJ,WJ,DJ and NJ.Under the background of 3‰ water retention agent treatment,the effects of microbial strains addition on root tensile properties were listed as follows in descending order: DJ,SJ,WJ and NJ.Under the background of 5‰ water retention agent treatment,the effect of microbial strains addition on root tensile properties was listed as follows in descending order: SJ,DJ,WJ and NJ.The addition of water-retaining agent reduced the tensile strength and tensile strength of the roots of Robinia pseudoacacia,and the difference in the tensile properties caused by the treatment of 3‰ and 5‰ water-retaining agent was not obvious.The mechanical responses of root microbial strains and water retention agents of Robinia pseudoacacia and Lespedeza bicolor were inconsistent.(4)The shear strength of the soil with added roots was significantly higher than that of the soil without added roots,and the increase of vertical load would increase the shear strength of the soil.For Robinia pseudoacacia,the combination of 5‰ water retaining agent and microbial strains inhibited the microorganism and weakened the influence of root development.In the absence of microorganism treatment,the shear strength of 3‰ water retaining agent treatment was the lowest,while that of 5‰ water retaining agent treatment was the highest.For Lespedeza bicolor,the shear strength of single microbe treatment was significantly lower than that of double microbial strains and three microbial strains treatment.Under 5‰ water retention agent treatment,the three microbial strains treatment was significantly higher than the other treatments.Compared with the roots of Robinia pseudoacacia,the shear strength of root-reinforced soil was increased by microbial strains and water retention agent.The addition of microbial strains and water retaining agent had a significant effect on the cohesion of the root-reinforced soil of Robinia pseudoacacia,but no significant effect on the friction Angle.(5)The growth of roots mainly depended on the changes of soil nutrients and soil enzyme activities,and the tensile properties of roots and the shear properties of root-reinforced soil mainly depended on the changes of lignin,cellulose and hemicellulose of roots.In addition,for Robinia pseudoacacia,lignin was greatly affected by soil characteristics.For Lespedeza bicolor,cellulose was affected by soil characteristics.In general,the addition of microbial strains to the substrate had a positive effect on the soil and root system,but the difference between the positive and negative effects caused by the waterretaining agent were unknown and further studies were needed to do.Therefore,the addition of microbial strains to external-soil spray seeding substrates can help plants strengthen the soil and assist with enhancing the efficacy and benefits of this strategy for the remediation of severely degraded ecosystems,such as abandoned mining areas. |
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