Study On Effect Of Straw And Biochar Returning On Soil Heavy Metal And Heavy Metal Accumulation In Rice Plant

As a major country of straw production,straw returning is one of a main method of recycling straws.Straw returning can minimize the damage caused by the heavy metals in soil,not only can it do so,but also solve the common problem that straws cannot be disposed without harm.However,research indicate that large amount of active organic substance including dissolved organic carbon(DOC)produced during the decay process of straws could activate heavy metals in soil.Rice is the main a mainly crop in China,the accumulation of heavy metal within rice has become a major environmental problem in recent years.There are still massive arguments about the effect of straw returning on the absorption of heavy metals in rice.In this study,pot experiments were carried out to investigate different methods of straw returning(direct straw returning and returning with biochar),as well the effect different amount of returning straws has on Bio-availability of heavy metal on paddy soil and the accumulation of heavy metals within rice,.Significant conclusions are illustrated as follows:1.Both of the pH level and the concentrations of DOC in soil leachate decreased as the rice grows.The application of straw and biochar elevated pH level in soil leachate,especially biochar,and a positive relationship between biochar application and the pH level in soil leachate.Straw returning elevated DOC level in soil leachate significantly,and a positive relationship between straw returning and DOC concentration in soil leachate was observed in this study.2.Biochar application elevated the concentration of Cr and decreased the concentration of Cu,Zn,and Pb in soil leachate significantly.Correspondingly,straw returning elevated the concentration of Cr and As and decreased the concentration of Cu,and Zn in soil leachate significantly in this study.3.In this paper,analytical methods three-dimensional excitation emission matrix fluorescence spectroscopy(3DEEM)were selected to investigate the composition of DOC in soil leachate,and discovered that there are main protein-like fluorescence andfulvie-like fluorescence.Straw returning elevated the concentration of protein-like fluorescence and fulvie-like fluorescence in soil leachate significantly.4.Subcellular localization analysis of the root and stem of rice in tillering and ripening stage indicates that Cd mainly exists in cell wall.Straw returning elevated the percentage of Cd in the cell wall and decreased the percentage of Cd in the cell soluble fraction.And the physical barrier playes a crucial role in plant defense response to toxic metals.5.Biochar application decreased the concentration of Zn,Pb,Cu,and As in rice plant significantly,and a negative relationship between the amount of biochar and the concentration of Zn,Pb and As.But it has no effect on Cd and Cr in this study.6.Straw returning decreased the concentration of Zn,Pb,Cd,and Cu in rice plant significantly,and a negative relationship between straw returning and the concentration of Zn,Pb,Cd,and Cu.But it has no effect on As and Cr in this study.