Biophysical And Chemical Properties And Heavy Metal Accumulation And Migration Characteristics Of Dominant Plants In The Rhizosphere Of Lead-Zinc Waste Dump

Northwest of Guizhou is a concentrated place of indigenous zinc smelting in history and has a long history of lead and zinc mining and smelting.Because indigenous zinc smelting is an ancient industry with extensive simplicity and a low metal recovery rate,it will leave behind exposed lead-zinc waste residue rich in heavy metals(Pb,Zn,Cu,and Cd,etc.)and form a large-scale lead-zinc waste residue pile.The heavy metals remaining in the waste residue are easily migrated to the surrounding aquatic and agricultural ecosystems through surface runoff and wind dispersion,thus posing serious threats and hazards to the surrounding ecological environment and human health.Ecological restoration or plant reconstruction of waste residue piles is an important means to control the spread of heavy metal pollution and improve the quality of the local ecological environment.However,most of the current research on phytoremediation is mainly based on indoor simulated herbal remediation andconsiders a single environmental factor.However,the physical,chemical and biological characteristics of the soil-plant-microbial interface with the participation of dominant plants are rarely reported.In this study,the dominant plants(Carex breviculmis,Buddleja davidii,Artemisia annua)around the lead-zinc residue pile and its surroundings,and actual soils(rhizosphere and non-rhizosphere)werecollected.Then combined with field sampling and indoor analysis,the heavy metal pollution,microbiological characteristics,overall distribution characteristics of soil fertility,the migration and enrichment characteristics of heavy metals to soil by plants and the distribution of nutrient elements in vivo were systematically studied,and the characteristics of heavy metal pollution and microbial interaction mechanism of lead-zinc waste residue site and surrounding areas were explored from the perspective of the plant-soil-microbial system.The results showed that:The three dominant plants of the slag pile can improve the living environment of the slag pile to varying degrees.Among them,Artemisia annua had higher effects on soil total nitrogen,available phosphorus,organic matter and moisture content than other dominant plants.The contents of Zn and Cd in the rhizosphere soil of Artemisia annua slag,the Cd and Pb contents of the rhizosphere soil of Buddleja davidii,and the contents of As and Pb in the rhizosphere soil of Carex breviculmis were significantly lower than those in the control soil.The increase of the effective state content of heavy metals was related to the increase of soil nutrient content,and the rhizosphere of Carex breviculmis effectively reduce the DPTA-Pb content in waste residue.The root systems of the three dominant plants can increase the enzymatic activities involved in carbon,nitrogen and phosphorus cycles to varying degrees,and Artemisia annua can increase the content of rhizosphere available carbon and phosphorus by influencing the enzymes related to soil carbon and phosphorus cycles,thereby effectively improving the soil nutrient status of slag piles.Microbial metabolism has phosphorus restriction on the non-slag pile,and nitrogen restriction in microbial metabolism on the slag pile,compared with other normal soil total nitrogen,total phosphorus,available phosphorus and organic matter play a more important role in affecting plant enzyme activity on the slag pile,heavy metal stress will increase the carbon limit of soil microorganisms.On the slag pile,Carex breviculmis for Cu,As and Pb,Buddleja davidii root for Zn,and Artemisia annua for Cd showed better enrichment ability than the other two dominant plants.On the non-slag piles,Carex breviculmis for Cu,Artemisia annua for Zn and As,and Buddleja davidii for Cd and Pb showed better enrichment ability than the other two dominant plants.The content of C and N in the dominant plant was low,the average carbon and nitrogen content of each organ of the plant on the residue pile was lower than that of the non-residue pile,and the averagephosphorus content was higher than that of the non-residue pile.Carex breviculmis and Artemisia annua showed obvious advantages in increasing the diversity and richness of rhizosphere bacteria and fungi.Microorganisms Gaiella,Nitrospira,RB41,Arthrobacter,Calcarisporiella and Sphingomonas are positively correlated with heavy metals,and they may play an important role in the bioremediation of contaminated soils.Both bacterial and fungal networks on lead-zinc residue are less complex than those around the slag,and the positive correlation ratio is higher,indicating that the soil microbial structure becomes more unstable with the increase of heavy metal pollution.