Effects Of Different Fertilizers On Cadmium Accumulation And Bacterial Community Structure In Tobacco Rhizosphere

Cadmium is one of the most toxic heavy metals,and plant extraction is a common remediation method for cadmium contaminated soil.Tobacco has a strong ability of cadmium enrichment,strong environmental adaptability,rapid growth and large biomass,so it is expected to become an ideal plant for cadmium contaminated soil remediation.Fertilization is an important agronomic measure to control the accumulation of heavy metals.However,it is not clear how fertilizer affects the absorption and accumulation of cadmium in tobacco.This study compared the effects of different nitrogen and potassium fertilizers on cadmium accumulation in tobacco through pot experiment,and clarified the rhizosphere microbial factors of urea promoting cadmium absorption in tobacco.The main results are as follows:(1)A pot experiment was used to analyze the effects of foliar application of potassium(potassium dihydrogen phosphate,potassium chloride and potassium nitrate)on the accumulation of cadmium in tobacco.The results showed that different potassium fertilizer treatments significantly increased tobacco biomass.Among them,potassium dihydrogen phosphate had the best effect,followed by potassium chloride and potassium nitrate,which increased by 62.6%,55.6%and 55.4%respectively compared with the control.Foliar potassium application did not significantly increase the cadmium content of tobacco plants,but increased the total amount of cadmium extraction.Among them,potassium nitrate treatment had the greatest promotion effect,which increased by 78.4%compared with the control.Potassium application reduced the effective cadmium content in the rhizosphere,which may be caused by the large amount of effective cadmium absorbed by tobacco;in addition,potassium application also reduced the rhizosphere pH,which may be an important reason for improving the cadmium accumulation ability of the plant.At the same time,it was also found that potassium application reduced the accumulation of trace elements such as Mn and Fe in tobacco.Therefore,foliar application of potassium nitrate is an effective agronomic measure to enhance the effect of tobacco repair.(2)Pot experiment was conducted to analyze the effects of different nitrogen fertilizers(urea,potassium sulfate and potassium nitrate)on cadmium accumulation in tobacco.The results showed that the application of three kinds of nitrogen fertilizer increased Cd content and Cd extraction of tobacco plants,and also increased plant height,root length and biomass of tobacco plants.Urea was the best treatment,which increased the Cd content in tobacco leaves by 50.6%-52.6%,plant height by 40.6%-50.0%,root length by 42.0%,biomass by 16.7%-13.5%,and total extraction amount by 63.4%-63.6%.Urea application significantly reduced the pH of rhizosphere,which may be an important reason for promoting cadmium accumulation in tobacco.In addition,it was found that the effects of different nitrogen fertilizers on iron and manganese contents in plants were similar to those of cadmium,indicating that cadmium and these elements may share ion channels and enter tobacco.Therefore,the application of urea is an effective agronomic measure to enhance the effect of tobacco restoration.(3)A pot experiment was conducted to study the effect of urea application on rhizosphere bacterial community structure.The results showed that urea treatment could significantly increase Shannon index,Chaol index and ACE index of rhizosphere bacterial community.Application of urea did not significantly change the bacterial community structure at phylum level,but significantly changed the community structure at genus level.Nitrogen application significantly increased the abundance of Sphingomonas.Because Sphingomonas has plant growth promoting function and cadmium activation function,Sphingomonas may increase root length,root surface area,and organic acid secretion.Therefore,the increase of Sphingomonas abundance under the condition of urea application may be an important reason for the increase of Cd accumulation in tobacco.At the same time,it was also found that the application of urea promoted the nitrification process of rhizosphere soil,decreased the pH of rhizosphere soil,and promoted the activation of cadmium in rhizosphere,which may be one of the important reasons for promoting the accumulation of cadmium in tobacco.