Effects Of Tobacco-stalk-biochar On Cd Contaminated Soil Remediation And Cd Uptake By Flue-cured Tobacco

Cd is a kind of heavy metal element that has a great threat to human life and health,which could transfer to human body from food chain in the soil-crop-food system.In recent years,the intensification of urban pollution and dramatic increase in the variety and number of agricultural chemicals leads to heavy metal pollution in the soil.Studies have shown that,tobacco-stalk-biochar,which is a product of carbonization of agricultural wastes,could repair the Cd contaminated soil when applying it to soil The paper takes flue-cured tobacco as a research object,tobacco-stalk-biochar as repair material,to study the improvement mechanism of tobacco-stalk-biochar on the remediation of Cd contaminated soil and the reduction effect on Cd content of flue-cured tobacco.The stabilization mechanism of Cd in brown soil and red soil was also studied by indoor simulation test.(1)The p H was significantly increased with the increase of tobacco-stalk-biochar rate in acid red soil,and when the tobacco-stalk-biochar application rate is 20 g·kg-1,the changes of soil p H from acidic to alkaline.The soil p H changes more smooth when applying tobacco-stalk-biochar to alkaline cinnamon soil.The content of organic carbon in cinnamon soil and red soil increased significantly with the increase of the amount of tobacco-stalk-biochar.After the application of biochar,the carbonate bound Cd,the organic bound Cd and Fe,Mn oxide-bound Cd in red soil increased gradually with the prolongation of culture period,which the three form of Cd increased in a volatility trend in drab soil.The soil organic carbon content and biochar application presented significantly negative correlation with the exchangeable Cd in cinnamon soil,yet had a great positive correlation with carbonate bound Cd,Fe,Mn oxide-bound Cd and organic-bound Cd.The p H,soil organic carbon content and biochar application presented significantly negative correlation with the exchangeable Cd in red soil,yet had a great positive correlation with other four types of Cd.However,the correlation coefficient in red soil is greater than that in cinnamon soil.(2)Soil Cd pollution inhibits soil enzyme activity,soil microbial biomass and soil respiration to varying degrees,while tobacco-stalk-biochar has a better effect on the biological characteristics of Cd contaminated soil.The amount of bacteria,fungi,actinomycetes,soil urease activity,soil microbial biomass carbon,soil microbial biomass nitrogen and soil respiration rate all showed a trend of increase after the application of tobacco-stalk-biochar.The soil p H and organic matter content showed an increasing trend as the growing season progressed.Soil p H and organic carbon increased with the increase of tobacco-stalk-biochar rate under the same level of Cd pollution.With the increase of biochar rate,soil available Cd content and exchangeable Cd content decreased significantly,whereas the soil carbonate bound Cd content,Fe-Mn oxide bound Cd content,organic bound Cd content and residual Cd content showed an opposite trend.(3)The plant height,stem circumference,leaf length,leaf width and effective leaves of flue-cured tobacco were significantly reduced under Cd stress,while the agronomic traits of flue-cured tobacco were significantly improved after the application of tobacco-stalk-biochar.Gas exchange parameters such as net photosynthetic rate and stomatal conductance of flue-cured tobacco decreased significantly with the application of Cd,which showed a trend of increase after application of tobacco-stalk-biochar.We find that the decrease of net photosynthetic rate of flue-cured tobacco was caused by non-stomatal factors when the Cd is 60 mg·kg-1.The Cd content and accumulation in Cd contaminated soil were regulated by tobacco-stalk-biochar.The content of Cd in tobacco plants decreased significantly with the increase of tobacco-stalk-biochar.In moderately contaminated soil,the total cumulative amount of Cd in tobacco plants decreased significantly with the application of tobacco-stalk-biochar.The enrichment coefficient of Cd in all parts of the tobacco plant decreased with the tobacco-stalk-biochar rate.The transport coefficient of Cd from the roots to the upper leaf,the roots to the middle leaf and the roots to the lower leaves of the tobacco plants was significantly increased when added Cd to soil,all the transport coefficients was significantly reduced after the application of tobacco-stalk-biochar.