Effect Of Piriformospora Indica Assisted Plants On Enhancing Remediation Efficiency Of Soil Contaminated By Cadmium And Chromium

In recent years,soil heavy metal pollution issues caused by human activities(such as industrial emissions,mining,smelting,and hazardous solid waste disposal)have become increasingly serious and attracted focused attention.Bioremediation has been growingly accepted by the public and has been developed widely for the remediation of soils polluted by heavy metals due to its advantages of high efficiency(especially for large areas and low pollution areas),low cost,easy availability,and harmless to the ecosystem.In this study,we simulated farmland soils with different pollution levels of Cd and Cr through pot experiments,to screen out Cd-Cr enriched plants with strong adaptability to climate conditions,soil type and large plant biomass in Hainan.The enriched plants combined with microorganisms were adopted to provide optional bioremediation materials and enhancing measures for soils contaminated with heavy metals in Hainan.The main research results are as follows.(1)In Cd-Cr compound contaminated soil,the four heavy metal enrichment plants,king grass(Pennisetum purpureum K.Schumach × Pennisetum thyphoideum Rich),Leersia hexandra,Helianthus annuus L.and Ricinus communisl,increased soil p H value and decreased soil electrical conductivity(EC)after remediation,which had a great influence on the concentrations of heavy metals in soils.King grass and Leersia hexandra showed strong tolerance to Cd and Cr in soils,exerted higher biomass,and significantly reduced the concentrations of Cd and Cr in soils.The removal rates of Cd and Cr in soils were 4.80%-11.7% and 0.60%-2.80% for king grass,1.50%-5.51% and 0.39%-1.34% for Leersia hexandra,respectively.(2)The synchrotron radiation X-ray microanalysis of roots of king grass showed that Cd and Cr in the roots of king grass were mainly distributed in vascular columns,but the vascular column channels for Cd and Cr transport in the roots of king grass did not overlap.(3)The plant-microbe combined remediation experiments revealed that P.indica could colonize and form symbionts in the roots of king grass and Leersia hexandra.The results showed that inoculation with P.indica significantly increased the biomass of plants(P<0.05),which facilitated the accumulation of heavy metals in plants,thus significantly improving the removal rates of soil Cd and Cr and enhancing the remediation effect.(4)Inoculation with P.indica significantly reduced soil p H and electrical conductivity(EC),and increased the bio-effectiveness of soil Cd and Cr,thus promoting the enrichment of heavy metals in king grass and Leersia hexandra.(5)Inoculation with P.indica significantly increased removal rates of Cr in soils by king grass with increases of 11.5%-72.8%,and significantly increased removal rates of Cd and Cr in soils by Leersia hexandra with increases of 16.1%-129% and 14.8%-128%,respectively.(6)The combination of king grass and P.indica is feasible phytoremediation measure for soils contaminated with light concentrations of Cd(≤0.6 mg/kg)and Cr(≤127 mg/kg).