| With the acceleration of industrialization and urbanization,the problem of soil heavy metal pollution has become increasingly serious.Repairing heavy metal pollution in soil has become an urgent problem to be solved.The combination of plants and microorganisms to repair heavy metal contaminated soil can fully utilize their respective advantages while making up for each other and greatly improving the repair efficiency.Rhizobium and leguminous plants co-exist with nodular nitrogen fixation,promote plant growth,enhance plant disease resistance and stress resistance,and its application and potential of symbiotic system formed with leguminous plants in heavy metal contaminated soil remediation have received extensive attention.White clover is a kind of excellent pasture and Greenland plant widely cultivated.It has been found to be resistant to copper and lead pollution.The economic development in the eastern part of China is rapid,the contradiction between the social artificial composite system and the natural ecosystem is sharp,and the abuse of agricultural production materials such as pesticides and chemicals is widespread,which leads to the increasingly prominent problem of heavy metal pollution in farmland soil.Although domestic scholars have conducted a lot of research on heavy metals in farmland soils in the eastern region,from the research scale,they are mainly provincial and county-level regions.There is no spatial distribution characteristics and pollution assessment of heavy metals in farmland soils in the eastern part.Therefore,It is of great significance to explore the overview of heavy metal pollution in farmland soils in the eastern region,and to carry out research on ensuring national food security and promoting regional soil and environmental interactions.Pot experiments were conducted to investigate the effects of Trifolium repens and Rhizobium trifolii on the restoration of Cu and Pb contaminated soil.The plant height,root length,shoot fresh and dry quality,underground fresh and dry quality,chlorophyll content,above-ground and below-ground N content of Trifolium repens inoculated with Rhizobium trifolii and non-inoculated Rhizobium trifolii were measured.The contents of Cu and Pb in shoots and shoots were investigated by single factor analysis of variance(LSD)to investigate the tolerance of Trifolium repens to Cu and Pb contamination.By comparing the growth characteristics of Trifolium repens and the characteristics of heavy metal absorption in the inoculated and non-inoculated groups,the effects of inoculation of Rhizobium trifolii on the repair of Cu and Pb contaminated soil by Trifolium repens were studied.In addition,this paper also obtains relevant data of heavy metals in farmland soils in eastern China from 2008 to 2018 from published literature,and uses geostatistical analysis and semi-variance function to obtain space for arsenic,cadmium,chromium,mercury and lead in farmland soils in eastern China.Distribution characteristics,based on the analysis of semivariograms,the Kriging interpolation,the visual expression of soil heavy metal pollution.According to the national environmental quality standards,the internal pollution index and the soil accumulation index were used to evaluate soil heavy metal pollution.The following research progress has been made:(1)The effect of inoculation of Rhizobium trifolii on the bioremediation of Cu-contaminated soil by Trifolium repens.The fresh weight of the aboveground and underground parts of Trifolium repens increased first and then decreased with the increase of treatment concentration.The low concentration of Cu played a certain role in promoting the growth of Trifolium repens.When the control group and Cu content were 500 mg.kg-1 and 1000 mg.kg-1,the inoculation of Rhizobium trifolii could significantly increase the biomass of the aboveground and underground parts of the Trifolium repens.The differences of chlorophyll a,chlorophyll b,total chlorophyll and chlorophyll a/chlorophyll b in Trifolium repens between different treatment groups did not reach significant levels.Cu stress and inoculation of Rhizobium trifolii had no significant effect on chlorophyll content of Trifolium repens.Trifolium repens has good tolerance to Cu,and the inoculation of clover rhizobia can significantly increase the biomass and Cu content in Trifolium repens at low concentration of Cu.Although the accumulation amount does not reach the standard of super-sludged plants,the symbiotic system of Rhizobium trifolii-Trifolium repens has high biomass and tolerance,and can be castrated many times,so it has a wide range application prospects in repairing Cu-contaminated soil.(2)The effect of inoculating Rhizobium trifolii on the bioremediation of Pb-contaminated soil by repens.As the amount of Pb added in the soil increased,the accumulation of Pb in the Trifolium repens resulted in a significant decrease in Trifolium repens biomass.Trifolium repens has certain enrichment characteristics for Pb.With the increase of Pb in soil,Pb content in shoots and shoots of increases.In the study,when the amount of Pb in the soil was 0,50,100 and 200 mg·kg-1,the N content in the lower part of the Trifolium repens was higher than that in the non-bacterial group,but the promoting effect was not significant.The difference of total chlorophyll a,chlorophyll b and chlorophyll in Trifolium repens between different treatment groups did not reach significant level.Pb stress and inoculation of Rhizobium trifolii had no significant effect on chlorophyll content of Trifolium repens.For the biomass and Pb content of Trifolium repens,the inoculation group increased compared with the non-bacterial group,indicating that the inoculation of Rhizobium trifolii could increase the biomass and Pb content of Trifolium repens,but the promotion effect was not significant.Rhizobium can reduce the toxic effect of Pb on Trifolium repens and increase the Pb content in the aboveground and lower parts of Trifolium repens,but the promotion effect has not reached a significant level.(3)Spatial distribution and evaluation results of heavy metals in cultivated soils in eastern China.The accumulation of Cd,Hg and Pb was more serious,and the mean values were 2.3 times,2.8 times and 1.4 times of their background values,respectively.Five kinds of heavy metal semi-variance best-fit models:The theoretical models of semi-variance functions of As,Cd,Cr,Hg and Pb are:spherical model,gaussian model,exponential model,an exponential model and a spherical model.The block-to-base ratio of Cr is less than 25%,and the spatial autocorrelation is strong.The block-to-base ratio of As,Cd,Hg,and Pb is between 25%and 75%,and the spatial autocorrelation is moderate.The range Pb>Hg>As>Cr>Cd,Pb has the strongest spatial distribution uniformity,and the spatial distribution of Cd is the most complex and variable.The Kriging interpolation results show that the heavy metal content of farmland soils in central Hebei Province and central Guangdong Province is generally higher.Secondly,farmland soils in Shandong Province,Jiangsu Province,Zhejiang Province and Fujian Province also distribute small areas of heavy metals.The results of the comprehensive pollution assessment of Nemero show that the comprehensive pollution in Guangdong Province is the most serious;the accumulation index shows that the Hg pollution of farmland soil is the most serious in the eastern region,followed by the mild pollution level of Cd and Pb,and the lightest pollution of As and Cr.The main innovations are as follows:First,the effects of the symbiotic system of Trifolium repens and Rhizobium trifolii on the repair of heavy metals were studied.As a high-quality legume forage,Trifolium repens has been found to have a certain potential for repairing Cu-contaminated soil.However,studies on the heavy metal contaminated soil with the Rhizobium symbiotic system have not been found in the literature.In this paper,the potted experiments were carried out to study the physiological responses of Cu,Pb,and Cu and Pb in the Trifolium repens inoculated with Trifolium rhizogenes,and the effects of Trifolium repens-Rhizobium symbiotic system on Cu and Pb contaminated soil were discussed.Second:the research scale of heavy metals in farmland soil has expanded to the eastern part of China.Domestic scholars have done a lot of research on heavy metals in farmland soils in China,but the research scales are mostly county-level and provincial-level regions.Due to the lack of relevant data,it is difficult to carry out soil heavy metal research above the provincial scale.In this study,based on the methods of bibliometrics,based on the previous studies,the spatial distribution and variation characteristics of heavy metals in farmland soils in eastern China were obtained by semi-variance function.The heavy metals in the soil of eastern farmland were studied by using the internal pollution index and the soil accumulation index.Pollution assessment.In conclusion,Pot experiments showed that Trifolium repens had good tolerance to Cu,and Rhizobium trifolii could significantly increase the biomass and Cu content in Trifolium repens at low Cu level.Although its accumulation does not reach the standard of super-stained plants,Rhizobium trifolii-Trifolium repens has a high biomass and tolerance,and can be castrated many times,so it has a wide range in repairing Cu-contaminated soil.In addition,the study found that Rhizobium trifolii can reduce the toxic effect of Pb on Trifolium repens and increase the Pb content in the aboveground and lower parts of Trifolium repens,but the promotion effect has not reached a significant level.Therefore,inoculation of Rhizobium trifolii to improve the repair efficiency of white clover on Pb contaminated soil needs further study.Compared with the background value of heavy metal soil in China,the accumulation of Cd,Hg and Pb is more serious,and the mean value is 2.3 times,2.8 times and 1.4 times of the background value respectively.The coefficient of variation of Cd is 0.913,which is a high degree of variation,indicating that the content of farmland soil in eastern China is susceptible to human activities;the spatial distribution of Pb is the strongest,and the spatial distribution of Cd is the most complex and variable.In addition,the accumulation of heavy metals situation is the most serious in Guangdong Province. |
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