Influence On Soil Biological Activity And Bacteria Community Diversity By Exogenous Lead And Cadmium

The increase of industrial refuse and the abuse of pesticide and chemical fertilizer,as the result of rapid economic development,has been one of the major reasons for environment pollution,especially to the heavy metal contamination.Metal contamination has significantly influenced the quality of farmland soil and agricultural products,which further threaten the people's health.So in this study,we chose two topic different physicochemical property of soil as research object;one was Lou soil?Eum-Orthic Anthrosols,weak alkaline?from Yangling,and the other wasred soil?faintly acid?from Jiangxi.After treatments with different concentration of heavy metal Pb and Cd for three years,the two soil samples were collected in winter and summer,respectively.The microbial biomass and soil enzyme activity effected by Pb and Cd were analyzed.Illumina MiSeq sequencing technology and statistical method were used to studythe response of microbial communities to different concentration of heavy metal Pb and Cd collected from Lou soil in winter and summer.Four lead-tolerant strains with two being fungus?numbered as Pb-W and Pb-9?and the others actinomyces?numbered as X-53 and X-68?were isolated from lead-contaminated Lou soil by plate selected method,their growth characteristic,as well as adsorption and removal rate of Pb²⁺.This study aims to understand the soil biological indicators and microbial communities changes influenced by heavy metals Pb and Cd in different types of soil,in order to establish an effective early warming and assessment system of soil polluted by heavy metal,which couldprovide theoretical reference and techical support for the bioremediation by microorganism.The main conclusions wereas follows:?1?The analysis of the effect of heavy metal Pb and Cd on soil microbial biomass carbon and microbial biomass quotient from different type of soil in winter and summer showed the content of microbial biomass carbon and quotient in soil treated by Pb and Cd both decreased comparing to CK treatments,and they were more sensitive than microbial biomass nitrogen to Pb and Cd,thus can be used as reliable indexs to indicate the soil quality contaminated by heavy metals.The urease and catalase activities affected by Pb and Cd had more differences inwinter orsummer.In summer,the activities of urease and catalase were activated by exogenous Pb,but inhibited in winter,indicating that different seasons had significant influences on urease activity.Both in winter or summer,the activities of catalase in Lou soil both increased with the concentration of Pb,but which is opposite in Red soil,of which the activities of catalase increased in low concentration of Pb and slightly decreased in high Pb treatment,indicating that catalase activity was related to concentration of heavy metal.The activity of enzyme in soil was also affected by different soil depth.Both in Lou soil and Red soil treated by Pb,the activities of catalase was not affected by soil depth,but only affected concentration of Pb;while the activities of catalase in Lou soil and Red soil treated by Cd had close relation with soil depth and concentration of Cd.The urease activities in 10-20 cm of Lou soil were more influenced by Pb treatment,and which in Red soil had no significant influenced by Pb treatment.The Cd treatments had more influenced on urease activities in10-20 cm of Lou soil,while which had more influenced on urease activities in 0-10 cm of Red soil.Of which it can befound that,Pb and Cd had different effects on urease and catalase activities in two topical soil in winter and summer,and whether the activities of enzyme were activated or inhibited depending on the concentration of Pb and Cd,and which had some correlation with physicochemical property of soil.Soil urease and catalase can be used as biological activity indicators to soil quality.?2?Pb could affect physicochemical propertiesof two soils in both winter and summer,especially in soil organic mater and rapid available P.Available Pb and total Pb had a negatively correlationwith soil organic matter?SOM?,but had a positive relationship with available phosphorus?AP?.High-throughout sequencing?Illumina MiSeq?technology of 16S rRNA genes hadbeen successfully used to reflect the changes of bacterial community structure at genus classic level affected by Pb.This study showed that Pb had a weak influence on the diversity of soil bacteria community at the classfication of phylum,class and order levels,but had significant effect at the genus level,the relative abundance of Bacillus,Streptococcus and Arthrobacter showed significant differences among three treatments,moreover,the three genera were heavy metal resistant bacteria.At the phylum level,the relative abundance of Actinobacteria and Acidobacteria were higher than others,which were the main phylum in the soil contaminated by Pb.The relative abundance of Cyanobacteria in high concentration treatment was higher than that in low and CK treatment,and the relative abundance of Gemmatimonadetes,Nitrospirae and Planctomycetes were negatively correlated with total Pb?TPb?.Collectively,the bacterial community structure was mainly similar in soils collected in winter and summer,while the diversity of bacterial in summer was slightly higher than that in winter.?3?Cd exerts a significant impact on soil bacterial community structure and soil physicochemical properties,and the seasonality also had effects in shaping soil microbial community.High bacterial diversity was revealed from the soil samples with 31 phyla.In winter,the abundance of dominant phylum Bacteroidetes,Gemmatimonadetes and Verrucomicrobia increased,but the Firmicutes decreased in Cd-contaminated soil in winter.While the abundance of Actinobacteria,Planctomycetes and Chloroflexi showed Cd dose-dependent patternin winter.In summer,the phylum Gemmatimonadetes and Verrucomicrobia decreased along with Cd dosing,while the dose-effect of Cd was found on the abundance of Actinobacteria and Chloroflexi.At genus level,57 genera of bacteria were significantly affected by Cd stress in winter,24 genera decreased,13 genera increased along with Cd gradients.In particular,genera Lactococcus,Psychrobacter,Brochothrix,Enhydrobacter and Carnobacterium disappeared in Cd treatments,suggesting high sensitivity to Cd stress in winter.In summer,1 genus decreased,9 genera increased with Cd dosing,and2 genera were dose-dependent.The contrasting effects of Cd on soil bacterial community could be due to different edaphic factors in winter?moisture,available phosphorus and total Cd?and summer?available Cd?.Collectively,the winter induced multiple stressors increase the impact of Cd on bacterial community in cropland.?4?Four lead-tolerant strains were isolated,two stains are fungus?Pb-W and Pb-9?,the others were actinomyces?X-53 and X-68?.Pb-W and Pb-9 had high tolerance to Pb²⁺with the concentration up to 4000 mg·L^-1.The Pb²⁺'s maximum resistance levels of strain X-68 and X-53 with the concentration up to 800 mg·L^-1.Using molecular biological identification technology,Pb-G and Pb-9 were identified as Penicillium and Sarocladium,respectively.X-53 and X-68 wered identified both as Streptomyces.Pb-G and Pb-9 had well removal efficiency of Pb²⁺when the concentration between 1000 and 2000 mg·L^-1,with the removal rate exceed 60%,while the removal rate of X-68 was 57.97%with the initial concentration of Pb²⁺at 500 mg·L^-1,which above the strain X-53.The adsorption rates and amounts of Pb²⁺by Pb-G were the best when the concentration at 1500 mg·L^-1,while the adsorption rates of strain X-68 reached to the highest level at a concentration of 400 mg·L^-1.