Study On The Biological Effect Mechanism Of Cerium And Zinc Composite Pollution In Maize-soil Environment

World wide,with the increasing dependence of people on rare earths in agricultural production and high-tech related fields,the production and scale of rare earth mining are increasing,resulting in various environmental pollution problems.Rare earth pollution is often accompanied by pollution from other heavy metals,and this composite pollution is more complex than single pollution.At present,there is limited research on the toxic effects and ecological functions of rare earth heavy metal composite pollution on crops.Therefore,this study uses corn as the test material,with Ce and Zn as representative elements of rare earth and heavy metals.Through pot experiments,the growth,nutrient absorption,oxidative damage,cell structure,and rhizosphere microbial community of corn under different treatments are analyzed and compared,Exploring the toxic effect mechanism of corn under Ce-Zn composite pollution,the molecular inhibition mechanism of nutrient absorption,and the ecological function of rhizosphere soil.The main research results of this article are as follows:（1）The combined pollution of Ce Zn has had an impact on the growth and development of maize.A single Zn/Ce concentration of 500 mg/kg has caused toxicity to maize,leading to a decrease in maize biomass.However,with the addition of 100 mg/kg Ce/Zn,the impact on maize biomass has been alleviated.When the composite pollution concentration reaches Ce500mg/kg-Zn500 mg/kg,the biomass of corn significantly decreases compared to CK,with a decrease of 26.67%.When the combined pollution concentration reached Ce750 mg/kg-Zn750mg/kg,the biomass of corn decreased by 37.33%compared to CK.When the combined pollution concentration reached Ce1000 mg/kg-Zn1000 mg/kg,the biomass of corn decreased by 47.78%compared to CK.The combined pollution of Ce Zn is more complex than the single pollution.Through stress research experiments,it is found that the threshold effect of the combined pollution of Ce Zn on the growth and development of maize exists:when the concentration of the combined pollution of Ce Zn is lower than the threshold concentration of Ce500 mg/kg-Zn500 mg/kg,there is a antagonism between the two pollutants,and when the concentration is higher than the threshold concentration,there is a synergistic effect between the two pollutants.（2）Ce-Zn composite pollution has caused oxidative stress on maize.Under the stress of Ce-Zn composite pollution,the ROS content of maize leaves and roots has increased.With the increase of Ce-Zn composite pollution concentration,the ROS content of leaf roots also gradually increases,showing an overall upward trend.Among them,the content of H₂O₂ in the leaves and roots of the Ce500 mg/kg Zn500 mg/kg composite pollution treatment group significantly increased by 2.70 times and 3.70 times compared to CK,respectively,and the content of O₂.^-in the leaves and roots significantly increased by 97.00%and 90.15%compared to CK.The content of H₂O₂ in the leaves of the Ce500 mg/kg Zn1000 mg/kg composite pollution treatment group was 2.31 times and 3.30 times higher than that of CK and showed a significant increase.The content of O₂.^-in leaves is 2.34 and 1.45 times that of CK,and significantly increases.The H₂O₂ content in the leaves of the Ce1000 mg/kg Zn500 mg/kg composite pollution treatment group was 2.70 times and 3.56 times higher than that of CK and showed a significant increase.The content of O₂.^-in leaves significantly increased compared to CK,2.42and 1.48 times higher than CK.At the same time,the ROS staining results of DAB/NBT maize on leaves and roots also confirmed this point.As the concentration of Ce-Zn composite pollution increases,the content of antioxidant enzymes POD,CAT,and SOD in the leaf roots also gradually increases,showing an overall upward trend.（3）Ce-Zn composite pollution affected the nutrient absorption of corn.The highest concentration of Ce-Zn composite pollution significantly decreased the C content by 11.24%and 5.42%compared to CK,N content by 43.36%and 44.14%compared to CK,P content by24.57%and 32.70%compared to CK,K content by 19.22%and 17.96%compared to CK,and Ca content by 20.19%and 34.51%compared to CK,respectively,Compared to CK,the Mg content significantly decreased by 8.00%and 5.34%,respectively.This is because Ce-Zn composite pollution affects the ion absorption rate of maize roots.The results indicate that the transport of K⁺and NH4⁺in maize roots is inhibited under high concentration composite pollution,while the transport of Ca²⁺is promoted first and then inhibited,that is,promoted at low concentration and suppressed at high concentration.（4）Ce-Zn composite pollution has affected and altered the soil ecological function of microbial community structure.Proteobacteria,Bacteroidota,and Actinobacteriota are more affected by heavy metal toxicity compared to other phyla,and the relative abundance of Proteobacteria decreases compared to the control group The relative abundance of Actinobacteriota has increased.High concentration of combined pollution changes the functional genes related to the carbon cycle（methane,methane oxidation,methylotrophy）,and also changes the functional genes related to the microbial nitrogen cycle（nitrate response,nitrate reduction,nitrogen response）,and inhibits the membrane transport function,signal transduction function Signal molecules and interaction functions.