The Composition Of Soil Organic Matter Bound Copper Pool And Its Response Of Adjunction Biochar

With the growth of population and the rapid development of social economy,a large amount of heavy metal pollutants get into the soil bv human production and living activities,it caused serious soil heavy metal pollution.Heavy metals in the soil will be enriched in the plant body and through the food chain take into the human body finally,it poses a serious threat to human health.It is an important research content of soil and environmental science to study the existence,transformation,migration and their mechanisms of heavy metals in soils,and the control and repair technology of heavy metal contaminated soil.In this study,the representative soils with low,middle and high organic matter content in tropical Hainan were selected(refer to SoilL,SoilM and SoilH).We contaminated the original soil to achieve different copper(Cu)contamination levels by adding different concentrations of copper nitrate,and then the aging culture experiments were carried out.To explore the ability of soil organic matter components to combine copper with different Cu contamination levels.Experiment soils were amended with corn straw biochar,and the biochar was added to SoilL and SoilM reaching the same carbon level based on the carbon content of SoilH.The impacts of exogenous biochar on different organic matter components bound Cu pools in soil were investigated,and the regulation effect of biochar to soil organic matter bound copper was preliminarily explored.Finally,the pot experiment of lettuce was carried out.The response of lettuce to copper stress and the relationship between soil organic matter components bound Cu pools and copper toxicity of lettuce were further studied to verify the regulation effect of biochar.The main results of this study are as follows:1 The amount of organic matter bound copper(Cu)in three experiment soils increased gradually with the increase of Cu contamination levels and reached the saturation.The Cu saturation capacity of soil was 18.25,3.13 and 2.34 mg· g-1,respectively.2 In the five organic matter components bound Cu pools of the three soils,the fulvic acid bound Cu of SoilL and the black carbon bound Cu of SoilH did not reach the saturation capacity,while the other organic matter components bound Cu all reached the saturation capacity.3 The sequence of saturated organic matter components bound Cu pools in SoilL is as follows:HA>GRSP>BC>POM>FA;The sequence of that in SoilM is as follows:GRSP>BC>POM>FA>HA;And the sequence of that in SoilH is as follows:FA>GRSP>HA>POM>BC.The order of copper content in SoilM and SoilL is:BC>POM>GRSP>FA>HA,and the order of that in SoilH is:HA>GRSP>FA>BC>POM within the study of the sorption saturated of five organic matter components in the three soils(replacing the unsaturated sorption with the maximum sorption amount).4 The contribution of different organic matter components to organic matter bound Cu pool changed with the increasing Cu contamination levels.Copper fraction in SoilL is mainly BC-Cu at low copper level,and BC-Cu and POM-Cu dominates with the increase of Cu level.BC-Cu and GRSP-Cu are major copper fractions in SoilM under low copper level,and BC-Cu account for the most with the rising of Cu level.While the main copper fractions in SoilH are FA-Cu and GRSP-Cu at low copper level,and HA-Cu and GRSP-Cu are the most two important fractions when Cu contamination level increasing.5 The addition of biochar can significantly change the organic matter components bound Cu of the soils.The amount of organic matter bound Cu in medium organic soil(soilm b)and low organic soil(soill b)added with biochar increased with the increase of Cu contamination level and gradually reached the saturation.Saturation capacity of organic matter bound Cu was 9.76 and 8.70mg·g-1 in SiolM+B and SoilL+B,respectively,3.12 and 3.69 times than that in SoilM and SoilL.6 The saturation capacity of FA-Cu,HA-Cu,GRSP-Cu and POM-Cu in SoilL+B was raised 1.71,2.83,2.75 and 0.09mg·g-1,respectively,than that in SoilL.Butsaturation capacity of BC-Cu was decreased 0.76 mg·g-1 in SoilL+B than that in SoilL.While the saturation capacity of FA-Cu,HA-Cu,GRSP-Cu and POM-Cu in SoilM+B was increased 1.66,3.75,2.68 and 0.07 mg·g-1,respectively,than that in SoilM.However,saturation capacity of BC-Cu was also reduced 2.14 mg·g-1 in SoilM+B than that in SoilM.7 The contribution order of biochar to five organic matter components Cu pool in SoilL and SoilM are all:HA>GRSP>FA>POM>BC.8 The lethal concentration of Cu to lettucein SoilL,SoilM and SoilH were 481.08,264.59 and 732.73 mg·kg-1,respectively.Interestingly,the lethal Cu concentration to lettuce in SoilL+B and SoilW+B were 674.51 and 515.00 mg·kg-1 after the addition of biochar.9 The limit value of Cu content in leaf vegetable was 10 mg·kg-1 taken from the standard of China(Tolerance standard of copper in foods).The Cu safety threshold to lettuce were 68.95,35.27 and 33.91 mg·kg-1 in SoilL,SoilM and SoilH under exogenous Cu contamination,respectively.The Cu safety threshold to lettuce in SoilL+B and SoilM+B were increased to 0.05 and 0.25 mg·g-1 with the amending of biochar.