Response Of Soil Microorganism To Atmospheric Cadmium Deposition And Passivation Remediation Of Cadmium In Typical Cadmium Contaminated Farmland Soil

With the rapid development of industry and agriculture in China,the problem of soil heavy metal pollution is becoming more and more serious,solving the problem of soil heavy metal pollution has become an important subject in the field of ecological environment.The state of soil inorganic pollutants released by the Ministry of Environmental Protection and the Ministry of Land and Resources shows that Cadmium pollution is the most serious.An important reason for its pollution is from atmospheric deposition,and the sources of atmospheric Cd deposition mainly include metal smelting,energy combustion,transportation and so on.Atmospheric Cd deposition directly affects the health of soil ecosystem when it enters the soil,but soil microorganisms are an important part of the soil ecosystem,which dominate the material circulation and energy flow of the soil and are important indicators for evaluating soil quality.At present,it is little known about the response of soil microorganisms to atmospheric Cd deposition,and the problem of soil cadmium remediation is extremely urgent.In this study,the soil selected in the farmland of Longshui Town,Dazu District,Chongqing was used as the tested soil,and five kinds of passivators were used as the test materials.The ideal passivator was selected by the simulation experiment of Cd deposition in indoor.Based on this experiment,the pot experiment of atmospheric Cd deposition and field situ experiment were carried out and determined by measuring microbe quantity,soil microbial biomass carbon and nitrogen,soil enzyme activity and bacterial community structure to discuss soil microorganisms for the response of typical regional atmospheric Cd deposition and passivation remediation of Cd in typical cadmium contaminated farmland Soil,which is expected to provide data support and theoretical basis for atmospheric environmental risk assessment and evaluation on the effect of cadmium passivation repair technology.The main results are as follows:1?The results of pure culture experiment showed that compared with CK,the addition of FeSO₄-Charcoal?FY?,humic acid?XZ?increased EXC-Cd?exchangeable cadmium?by 12.2%and 18.3%,respectively,while adding lime?LP?,calcium-magnesium-silicon fertilizer-organic matter?OCP?,calcium-magnesium-silicon fertilizer?FS?reduced EXC-Cd by 52.4%,14.2%,25.4%,respectively.LP,OCP and FS were further compared,it was found that both LP and FS significantly increased CA-Cd than CK,but there was no significant difference between OCP and CK.Both OCP and FS significantly improved Fe-Mn-Cd compared with CK,and OCP was significantly higher than FS?P<0.05?.For OM-Cd and RES-Cd,LP,OCP and FS have no significant difference from CK.In addition,the addition of FY,XZ and FS increased the content of easily absorbable Cd?EAC-Cd?and decreased the content of Cd?DAC-Cd?in plant.After adding OCP and LP,The EAC-Cd content was decreased and DAC-Cd were increased.In conclusion,OCP was selected as pot experiment and field experiment,and LP was selected as a control for OCP.2?The results of pot experiment showed that the fresh biomass and water content of mustard and corn treated with CK?blank?under Cd deposition were lower than those without Cd deposition,while the Cd content of plant was opposite.Whether Cd or no Cd deposition group,Cd contents in mustard and maize treated with OCP were lower than those treated with CK and LP.The study on soil microorganisms found that the number of bacteria,fungi and actinomycetes of CK,LP and OCP with Cd deposition was lower than that without Cd deposition by 14.2%⁷2.4%.Studies on MBC and MBN showed that atmospheric Cd deposition reduced MBC content,but increased MBN content.The results of field experiment showed that the application of LP or OCP significantly reduced Cd content of mustard and maize,but had little effect on plant biomass and water content.At the same time,both LP and OCP treatment increased the number of soil actinomycetes reaching 43.3%,152.6%,282.2%and 228.6%,respectively,but both reduced the number of fungi.In addition,LP treatment tended to reduce the number of bacteria,while OCP treatment tended to increase the number of bacteria.Studies on MBC and MBN showed that application of LP or OCP increased MBN content by 7.2%and 307.5%,19.1%and 41.1%,respectively.Moreover,application of OCP significantly improved MBC content?P<0.05?,while application of LP had little effect on MBC content.3?The results of pot experiment on soil enzyme activities showed that the activities of soil sucrase,urease,acid phosphatase and catalase of CK,LP and OCP with Cd deposition were lower than without Cd deposition by 1.6%³8.8%.Correlation analysis shows that there was significant or extremely significant negative correlation between atmospheric Cd deposition and soil enzyme activity?P?0.05,n=18 or P?0.01,n=18?.In addition,OCP treatment increased the activities of sucrase,urease,acid phosphatase and catalase in mustard and corn soil.Compared with LP and OCP,the soil enzyme activity of OCP treatment was higher than that of LP treatment.Field experiment results showed that the application of LP and OCP increased the activities of sucrase,urease,acid phosphatase and catalase in mustard and corn soil compared with CK,and the soil enzyme activity of OCP treatment was higher than that of LP treatment,which was similar to the results of the pot experiment.4?The results of soil bacterial community structure and diversity showed that the Chao1 index,ACE index and Shannon index of soil bacteria were significantly increased by adding calcium-magnesium-silicon fertilizer and organic matter?OCP??P<0.05?.Compared with OCP and Cd-OCP,the Chao1 index of Cd-OCP was significantly higher than OCP in corn soil?P<0.05?,while ACE and Shannon index were not significant differences.Studies on the phylum level of soil bacteria showed that OCP treatment increased the abundance of Proteobacteria,Gemmatimonadetes and Bacteroidetes in mustard and corn soil by 14.0%³6.4%.Compared with OCP and Cd-OCP treatment,Cd-OCP treatment reduced the abundance of Actinobacteria and Proteobacteria in mustard and corn soil by 2.4%¹4.2%.Studies on the genus level of soil bacteria showed that the OCP treatment has mainly increased the abundance of norank_fGemmatimonadaceae,norank_fElev-16S-1332 and Sphingomonas by 26.8%,25.4%and 55.5%in mustard soil,respectively,meanwhile,the abundance of Bacillus and Micromonospora was increased by 69.1%and 118.5%in corn soil,respectively.On the contrary,the Cd-OCP treatment reduced the abundance of these soil dominant bacteria.5?Studies on soil physical and chemical properties found that compared with CK,OCP treatment significantly increased pH of soil?P<0.05?,and decreased EXC-Cd content of soil that reached a significant level in corn soil by 2.3%and 46.3%?P<0.05?,while had no significant effect on TP and TK content.Compared with Cd-OCP,the TN and TP contents of Cd-OCP treatment were higher than those of OCP treatment and reached a significant level in corn soil?P<0.05?,while the pH and TOC content are just the opposite.Meanwhile,the content of EXC-Cd treated with Cd-OCP was significantly higher than that of OCP in mustard and corn soil?P<0.05?.Association analysis of soil bacterial community structure and environmental factors in mustard and corn soil treated with CK,OCP and Cd-OCP showed that TN,pH and EXC-Cd contents of soil were the main environmental factors affecting the bacterial community structure.