Absorption Of Heavy Metals In Compound Heavy Metal Contaminated Farmland By Ryegrass And Changes Of Bacterial Community In Rhizosphere Soil

The farmland soil around the mining area is seriously polluted by heavy metals,under the stress of heavy metal pollution,the soil microbial community structure will make a complex response.Plant rhizosphere microorganisms could promote the absorption of heavy metals by plants and were the key influencing factors for the transfer of heavy metals from soil to plants.In-depth study of the absorption of various metals by plants in soils contaminated with heavy metals,especially the changes in microbial community structure in the rhizosphere during remediation,for revealing the indicating effect of soil microorganisms on the degree of pollution,it is of great theoretical and practical significance to promote phytoremediation technology in the practical application of heavy metal compound pollution of farmland soil remediation.In this study,the compound pollution of heavy metals in the surrounding area of Tongling mining area was selected to evaluate the compound pollution degree of heavy metals,and the structure of the soil bacteria community and its dominant species in the area were analyzed.Under the condition of not adding any exogenous heavy metals,the potted experiment was used to select the ryegrass as the remediation plant,and the clean soil of the Agricultural Excavation Garden of Anhui Agricultural University was selected as the control to study the effect of ryegrass on the repair of different heavy metals in the compound contaminated farmland soil in the mining area.The 16 S rDNA Illumina high-throughput sequencing technology was used to analyze the bacterial community structure and its dominant bacteria in the rhizosphere soil before and after planting ryegrass,to determine the degree of soil cleanliness,and to explore the potential role of plant rhizosphere bacterial communities in the enrichment of soil heavy metals in plants.Screening for bacteria that are indicative of heavy metals provides the basis.Because the soil near the mining area was contaminated by heavy metals for a long time,the soil microorganisms may have resistance to one or more heavy metals,and compared with the clean soil of the control group,it is important to screen out bacteria that are resistant to heavy metals.The main results are as follows:1.The single-factor index method and Niemolu comprehensive pollution index method were used to evaluate the heavy metal pollution of the tested soil.The Cu,Zn,As,and Cd in the farmland soil near the Tongling mining area exceed the secondary standards of the “Soil Environmental Quality Standard”,which is a serious pollution ofcompound heavy metals;the control group Annonda Agricultural Extraction Garden soil is a clean soil,the measured heavy metal elements were not exceeded.2.The ryegrass had a certain absorption of heavy metals in Cu,Zn,and Cd.The maximum contents of heavy metals in the upper ground were Cu 589 mg/kg,Zn 412mg/kg,As 34.18mg/kg and Cd 4.25 mg/kg.So Ryegrass could be used as an effective plant to remediate compound heavy metal contaminated soils.3.There were abundant bacterial groups in farmland soils that were tested for combined pollution with heavy metals,and its dominant bacteria phylums are:Proteobacteria,Actinobacteria,Acidobacteria,Chloroflexi,and the dominant genuses are Gemmatimonas,Arthrobacter,Nocardioides,and Sphingomonas.The dominant bacteria in the control group were Proteobacteria,Actinobacteria,Acidobacteria,Gemmatimonadetes,and Saccharibacteria;the dominant bacteria were Gemmatimonas,Arthrobacter,Nocardioides,Sphingomonas,OM43-clade,and Pseudomonas.Under the activation of ryegrass,both the number of dominant phylums and the number of dominant genuses increased in both soils,but the soil OTUs increased more in the soil of the control clean group than in the compound contaminated soil.After 60 days of ryegrass cultivation,there were no significant changes in soil heavy metal content,heavy metal content in the upper part of the ryegrass land,and microbial structure in the rhizosphere soil at 30 days.4.The correlation between heavy metals and different bacteria was different,but the correlation between the total metal and available cotent and bacteria was the same.At the level of bacteria phylum,there was a significant negative correlation between Gemmatimonadetes and Cu,Zn,As and Cd in the soil,Chloroflexi was positively correlated with soil Cu,Zn,As,Cd.At the bacterial genus,Arthrobacter was highly positively correlated with soil Cu,Zn,As,Cd.