The Response And The Combined Phytoremediation By The Reclaimed Plants In Different Plant Configuration Modes And Their Associated Rhizosphere Microbiota In The Gejiu Tailing Ponds

As the well-known Kingdom of nonferrous metals.Yunnan province has to face the serious heavy metal pollution in the soils due to the previous intensive activities of nonferrous metal mining and smelting,especially in the large-scale mining wastelands,e.g.metal tailing ponds,slag heaps,where the soils are susceptible to serious erosion due to substrate characteristics and high precipitation.Thus,it is an alternative and economic way to construct a plant cover/cap to prevent the spread of soil metal contaminants by wind and water erosion,and meantime the plant cover also improves and rescues the soil quality by the combined phytoremediation by the interactions of diverse plants and their root associated-microbiota.In the present study,plant and soil samples of two plant species from the reclaimed areas with a single dominant species of(monodomnant)Populus yunnanensis Dode(sPy),Coriaria nepalensis Wall.(sCn),and two-species mixed communities(mPy-Cn),in Huangmaoshan tailing ponds,in Gejiu,Yunnan,Southwest China were collected,and the unreclaimed mining dumps were also collected and sampled as the negative controls(CK).And the response and the combined phytoremediation by plants and their associated soil microbiota(including bacteria and fungi)were characterized to evaluate the options of two dominant tree species in the different plant configuration modes(tree stand model(TSM),shrub stand model(SSM),and tree-shrub stand model(TSSM))in a new reclamation metal mining field.The main results were presented as folloxws:(1)Our results revealed that the soils were polluted seriously by excessive metals,with a range of 2833.83-2978.35 mg/kg Pb,586.72?785.85 mg/kg Zn,51.91?103.30 mg/kg Cd in Huangmaoshan Tailing ponds,in Gejiu,Yunnan,Southwest China,which are far higher than the third class values of Environmental Quality Standard for Soils of China.We found that the revegetation of two plant species significantly reduced the total and HCl-extractable metal concentrations of Pb,Zn and Cd than those of the bare control soils.Especially,it's true for the soils from the mixed stands with the minimum concentrations for the total and extractable Zn and Cd,and the lowest Pb concentrations occurred in the sCn soils.(2)Compared to the bare soil controls,vegetation reclamation of two plant species significantly improved the soil qualities,including the enhanced contents of organic matter,total nitrogen,total potassium,available nitrogen,available phosphorus and available potassium in soils.Especially it's true for the sCn and mPy-Cn soils.In addition,Vegetation reclamation also significantly increased the activities of several enzymes and the contents of glomalin-related soil protein(GRSP)in the soil.For example.Compared with the bare CK soils,sCn significantly increased the activities of?-glucosidase,urease,dehydrogenase and sucrase,the significantly higher activities of?-glucosidase,urease,alkaline protease and alkaline phosphatase for sPy;mPy-Cn significantly increased the activities of ?-glucosidase,urease.sucrase,alkaline protease and alkaline phosphatase;mPy-Cn and sPy significantly increase the content of total GRSP and easily extracted GRSP.(3)Obviously,there was a distinct pattern for the metal accumulation(Pb,Zn and Cd)of two plants species.We observed that most Pb ions were absorbed and accumulated in two plant roots,The Coriaria nepalensis Wall great potential use for the Pb phytostabilization of P.yunnanensisee.in metal-polluted soils.Interestingly,we also noted that the co-colonization of significantly lowered the Pb BCF of C.nepalensis than those of C.nepalensis in shrub stand model(SSM).P.yunnanensisecould accumulated a good deal of Zn and Cd ions in the roots,especially the higher Cd accumulated in twigs,and Zn and Cd in leaves,with both BCF and TF>1.(4)Evidence from the PLFAs data showed that vegetation reclamation can effectively enhanced the activities of microbiota colonizing the soils than that in the bare CK soils.The colonization of two plant species significantly promoted the total biomass of microbiota(including bacteria and fungi),and the enhanced biomass of bacteria colonizing the sPy soils,and fungal and G+ bacterial PLFAs in the mPy-Cn soils.NGS data showed that vegetation reclamation increased the significantly of Chaol,ACE,Shannon for bacteria and fungal Chaol,ACE indexes.We also noted that there a distinct communitie of the most dominant bacterial and fungal taxa,especially it was true for the fungi.RDA analysis further revealed the change of rhizosphere microbiota resulted from the alternative TN,TK,AK and SOM for bacteria,but for fungi due to the enhanced TP,AP,extractable Cd and Pb.The extractable heavy metal have greater effects on bacteria and fungi than the total heavy metal.In conclusions,the reclamation of two pioneer trees significantly improved the soil physiochemical quality,and enhanced the diversity of rhizosphere microbiota.Interestingly,these two tree species could accumulate a large amount of Pb in their roots with a great Pb phytostabilization potential,and the phytoextraction of both Zn and Cd by P.yunnanensis shoots.Our results showed that the mixed stands of two tree species had a synergistic effect on the improved soil quality and the promoted diversity of rhizosphere microbiota.