| Based on the severe fact that the heavy metal pollution of farmland soil is more prominent at present and the actual demand of "Soil Ten" for the safe utilization of polluted farmland.In this paper,paddy fields in a district and county of Guiyang were selected as the research object,and rice varieties in the field were screened through field plot experiments to analyze and compare the absorption amount of cadmium and lead in the above-ground part of different rice varieties,so as to screen out low-accumulation rice varieties suitable for local planting.Based on the low accumulation varieties,the indoor pot experiment was conducted to compare the activity of cadmium and lead in paddy soil and the content of cadmium and lead in rice under different passivation-foliar barrier combinations,so as to determine the best regulatory combination.The distribution of chemical binding states of cadmium and lead in potting soil,soil enzyme activities and microbial community results were analyzed,and the possible mechanism of the optimal regulatory combination to inhibit the absorption of cadmium and lead in rice was preliminarily discussed.The main results are as follows:(1)The cultivated soil in the study area was mainly polluted by Cd and Pb.The contents of Cd and Pb in paddy soil were 3.80 and 8.79 times of the background values in Guizhou Province,respectively.The contents of Cd and Pb in dry land were 5.20 and 13.04 times of that in Guizhou Province,respectively.The soil comprehensive pollution index of paddy field ranged from 1.64 to 4.23,of which 60% were heavy pollution grade.The comprehensive pollution index of dryland soil ranged from 1.94 to5.74,of which 50% were heavy pollution.(2)In 20 rice varieties,according to the low absorption and yield of cadmium and lead.They were high yield and low Cd type rice(Yixiangyou 2905,Chuankangyou 6107),high yield and low Pb type rice(Long8 Youhuachan,Rong3 You 533),low yield and low Pb type rice(Jingliangyou 534,Yiyou 2018)and high yield and low Cd and low Pb type rice(Baixiangyou 005,Yixiangyou 2905),respectively.(3)Single application of foliar barrier could also increase grain fresh weight,tillering number,plant height and stem and leaf biomass of rice.Nutritive control agent-foliar barrier agent and iron-base sulfur-rich material-foliar barrier agent treatment had the best effect on rice yield increase,except plant height decreased,tillering number,fresh weight of aboveground part and root length increased.Although the single application of foliar barrier can reduce the content of Pb in milled rice,but the content of Cd in milled rice increases,which has food safety risks.However,when adding iron-based biochar and iron-based sulfur-rich materials to the soil,combined with spraying foliar barrier,the contents of Cd and Pb in mrice decreased by 34.29%,8.57%,and 57.54%,57.42%respectively.(4)The distribution patterns of Cd and Pb in rice rhizosphere soil are different.Cd is mainly composed of residue and carbonate binding state,while Pb is mainly composed of residue and iron and manganese oxide state.The application of passivating agent and foliar barrier can promote the conversion of soil Cd and Pb from unstable state to stable state.The combined application of passivating agent and foliar barrier affected soil enzyme activities,and the activities of urease and alkaline phosphatase increased under the treatment of iron-based biochar and foliar barrier and iron-based compound sulfur material and foliar barrier.Soil urease activity was significantly increased,while alkaline phosphatase,dehydrogenase and catalase activities were decreased under the treatment of nutrient barrier and foliar barrier.Single application of foliar barrier can improve the activities of four enzymes,alkaline phosphatase activity increased significantly.(5)Proteobacteria,Chloroflexi,Acidobacteriota and Bacteroidota were the dominant phyla in rhizosphere soil of rice.Chloroflexi richness was improved with the exception of foliar barrier,a nutrient inhibitor.The changes of microbial community structure were closely related to soil enzymes and p H.(6)Iron-based biochar and iron-based sulfur-rich materials combined with leaf barrier can synchronously regulate the absorption of Cd and Pb in rice,and the contents of Cd and Pb in milled rice meet the national standards.The regulatory mechanisms may be as follows: first,the transformation of Cd and Pb in soil from an unstable state to a stable state is promoted by regulating the microenvironment of rhizosphere microdomain(p H value,soil enzyme activity,microbial community structure);Secondly,it regulates the transport of Cd and Pb in rice plants,storing most of Cd and Pb in roots,and transferring more Cd and Pb in above-ground parts to stems,leaves and rice husks. |
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