Study On The Remediation Effect Of Soil Amendments And Actinomycetes On Cadmium(Cd)Contaminated Farmland

Soil heavy metal pollution is one of the most serious environmental problems in China at present,and soil cadmium?Cd?contamination has the widest coverage in it.Therefore,more economical and efficient remediation methods are needed for the remediation of soil Cd pollution.In this study,different soil amendments[biochar,organic fertilizer and calcium hydroxide?Ca?OH?₂?]and biocontrol actinomycetes?mixed solid actinomycetes inoculant of Streptomyces roche D74 and Streptomyces partum Act12?were applied to Cd-contaminated farmland to explore the growth conditions of wheat,Cd contents in plants and soil,soil physicochemical properties,rhizosphere bacterial communities and the relationships among them during the restoration process,in order to evaluate the actual application effects of different remediation treatments and their effects on soil microecological environment.This study can provide a theoretical and practical basis for the establishment of a new remediation technology system for Cd contaminated soil.The main results of this study are as follows:?1?The remediation treatments increased the resistance of wheat under Cd pollution by increasing wheat antioxidant enzyme activity and photosynthetic capacity,and reducing the degree of wheat oxidative stress.Compared with the control treatment,different repair treatments increased the activity of superoxide dismutase?SOD?in wheat leaves by19.33%-37.78%,decreased the content of malondialdehyde?MDA?by 13.38%-28.36%,and increased the content of chlorophyll by 5.82%-15.80%.The actinomycetes played a leading role in improving the antioxidant activity of wheat leaves.In addition,the application of soil amendments had obvious growth promotion effects on the plants in the middle and late stages of wheat growth,which increased the aboveground biomass of wheat by9.79%-31.35%compared with the control.Applying biochar and organic fertilizer increased the theoretical yield of wheat,and the actinomycetes made the wheat grain fuller.The remediation treatments can reduce the accumulation of Cd in wheat grains by 17.87-32.44%.The application of organic fertilizer and Ca?OH?₂ reduced the accumulation of Cd in wheat.Applying biochar and Ca?OH?₂ effectively reduced the Cd translocation factors?TF?in plants;?2?The physicochemical characteristics of the amendments made it significantly change the soil physicochemical properties after being applied.Applying organic fertilizer made the content of soil nutrient elements significantly increased,and combined it with actinomycetes further improved the availability of nutrients in the soil.The soil physicochemical factors changed regularly during the process of wheat growth,and the growth of wheat had greater impacts on soil organic matter,nitrate nitrogen?NO₃^-?,available potassium?AK?and cation exchange capacity?CEC?than the remediation treatments.There were significant differences in contents of soil NO₃^-,AK and available phosphorus?AP?between wheat growth periods;?3?Different remediation treatments reduced the total Cd?TCd?and available Cd?DTPA-Cd?contents in soil,and the actinomycetes mainly affected soil DTPA-Cd contents.The application of Ca?OH?₂ and actinomycetes significantly reduced the ratio of soil available Cd to total Cd at the jointing stage and maturation stage of wheat,respectively,by20.96%and 18.46%.Organic fertilizers combined with actinomycetes significantly reduced the total soil Cd content at wheat maturation stage by 24.11%.The DTPA-Cd and TCd contents in soil decreased with wheat growth,and the Cd content of soil treated with organic fertilizers and actinomycetes changed the most during wheat growth;?4?The composition and structure of the bacterial community in wheat rhizosphere soil were significantly affected by the application of amendments.Applying organic fertilizers increased the abundance and diversity of the bacterial community,while the Ca?OH?₂reduced it significantly.The applications of organic fertilizers and Ca?OH?₂ were the main factors affecting the structure of the community.There were significant differences between the microflora of wheat rhizosphere and the original soil.The wheat rhizosphere soil microflora was more abundant than the original soil,while the diversity was lower.?5?There was a certain relationship between the Cd content in the environment,the soil physicochemical properties and the bacterial community of wheat rhizosphere.The application of organic fertilizer was the main factor affecting the soil physicochemical factors and bacterial community.Applying organic fertilizer significantly affected the content of ammonia nitrate?NH₄⁺?,NO₃^-,AP,AK and CEC in the soil.The soil NH₄⁺content had a significant positive correlation with the TF and Cd accumulation contents in wheat aboveground parts.While the NO₃^-content was significantly negatively correlated with it.Soil AP and AK contents had significantly negative correlation with plant Cd accumulation and bioaccumulation factor?BF?,while soil CEC amount and AK contents were negatively correlated with TCd content.The abundance of Verrucobacterium in the wheat rhizobacteria community was significantly positively correlated with soil AP,AK NH₄⁺and NO₃^-,and had a strong negative correlation with NO₃^-content.The Ca?OH?₂ increased the relative abundance of Proteobacteria and Bacteroidetes in bacterial community,and reduced the abundance of Pneumobacteria and Acidobacteria.Acidobacteria and Planctomycetes were significantly positively correlated with the ratio of soil DTPA-Cd to TCd,while Proteobacteria and Bacteroides were strongly negatively correlated it.?6?Comprehensively considering the effects of different treatments on wheat and soil micro-ecological environment and the actual effect of remediation,biochar and organic fertilizer treatments can be used as ideal remediation strategies after the application of actinomycetes.The organic fertilizer treatment has better repairing effect and is economical and environmentally friendly.The biochar treatment has acceptable remediation effect and has little impact on the soil micro-ecological environment.The results of this study need to be further verified in future researches on larger repair areas,longer continuous repair years,and more in-depth exploration of repair mechanisms.