Effects Of Microbial-induced Calcium Carbonate Precipitation On Root And Heavy Metal Enrichment Of Dominant Plants In Copper Tailings

Northwest China is home to densely distributed coal mines and non-ferrous metal mines,with a large number of historical open-pit tailings.High wind erosion in the region results in strong diffusion of mineral dust pollutants,which can cause the enrichment and pollution of heavy metal content in the surrounding atmosphere,soil,water sources,plants,and fruits and vegetables,posing a major threat to environmental safety and human health.The region’s arid climate and saline-alkali soil make it difficult to apply traditional mine restoration technologies such as phytoremediation.Microbially Induced Calcium Carbonate Precipitation(MICP)is a new technology that utilizes microorganisms for in-situ remediation of tailings pollutants.It offers advantages such as timeliness,environmental friendliness,and no secondary pollution,making it suitable for arid and saline-alkali soil habitats.However,the distribution characteristics of heavy metals in the soil and plant roots of the mining area,as well as the mechanism of potential ecological risks after the application of MICP technology,are still unclear.It is therefore essential to study the effect of MICP on root and soil characteristics,as well as the heavy metal enrichment ability of tailings plants,to promote the use of MICP for mine ecological restoration technology in the northwest region.To address these issues,this study selected a copper-silver mine in Zhongwei City,Ningxia Hui Autonomous Region as a representative area.Lysinibacillus fusiformis,Suaeda salsa,and Reamuria songariea were used to conduct tailings pollution solidification experiments in arid and semi-arid areas with high wind erosion.In this experiment,a cementation solution made of spindle-type L.fusiformis(OD600=2.02),urea,and calcium chloride was sprayed onto the tailings soil.The study investigated the effects of MICP cementation solution on uproot power and tensile strength of plant root and shear strength of root-soil composite.Changes in soil enzyme activity,nutrient content,root growth status,and root chemical composition were also analyzed to explore the response mechanism of root mechanical properties to MICP.These findings provide an effective way for the continuous restoration and improvement of ecological environments in contaminated mining areas.Furthermore,it is essential in guiding vegetation restoration and plays a vital role in improving the natural environment in the mining area.(1)Following MICP treatment,the heavy metal element content in the tailings soil decreased,and the nutrient content and enzyme activity significantly increased.In the plant rhizosphere soil,heavy metal concentrations were lower after MICP cementation compared to tailings soil,and the biological activity of Total Carbon,Total Nitrogen,Total Phosphorus,Total Potassium,catalase,sucrase,and urease was significantly higher.Heavy metals in the plant rhizosphere were mainly present in the residual state.(2)MICP treatment promoted the growth of Suaeda glauca and Reaumuria soongorica roots.Root length,diameter,and surface area of the two plants significantly increased compared to pre-cementation levels,and the content of lignin,cellulose,and hemicellulose in the roots also increased.The tensile and shear strength of the roots of Suaeda glauca and Reaumuria soongorica increased.The uproot power of Reaumuria soongorica roots showed a significant negative correlation(P<0.05)with hemicellulose and a significant positive correlation(P<0.05)with cellulose,while the tensile strength was opposite.(3)MICP treatment significantly reduced heavy metal content in the plant rhizosphere soil,thereby reducing heavy metal accumulation in plant roots.Heavy metal content in the rhizosphere soil was significantly negatively correlated with Organic Matter,Total Nitrogen,Total Phosphorus,pH,catalase,and urease in the rhizosphere soil(P<0.05).Heavy metal elements(except Cu and As)and sucrase showed a significant negative correlation(P<0.05)and a very significant positive correlation(P<0.05)with conductivity.Additionally,MICP treatment reduced the potential harm of heavy metals to the ecological environment and human health,especially after plant growth.(4)The shear properties of the root-soil composite were mainly affected by nutrient content,enzyme activity,and the initial vertical load of tailings soil.Organic Matter,Total Phosphorus,Total Nitrogen,Total Potassium,sucrase,and urease of the rhizosphere soil were significantly positively correlated(P<0.05)with the shear strength of the root-soil composite.Cellulose and hemicellulose also had a certain effect on the shear strength of the root-soil composite.