Adsorption Characteristics Of Four Organic Materials To Pb(?) And Their Effects Onsoil And Wheat In Pb-contaminated Field

Lead?Pb?is a typical heavy metal pollutant in the environment,which canbe enriched in water and soil.Lead pollution in soil causes serious consequences to the ecological environment quality,grain production safety and human health.The wastes produced in agricultural production,such as straw,livestock manure and so on can be used as in-situ remediation materials for heavy metal pollution,which is important for promoting the resource utilization and the sustainable economic development.However,the adsorption properties of different organic materials are different,and the effects of organic materials on heavy metal polluted farmland are affected by many factors.Therefore,maize straw,chicken manure,mushroom cultivating residue and sawdust biochar were chosen as remediation materials in this experiment,and the physical and chemical properties of these materials as well as their adsorption properties of Pb²⁺ were studied.Based on the above analysis,the effects of these four materials on the lead-contaminated wheat field were mainly investigated,including soil physical and chemical properties,soil microbial community structure and diversity,heavy metals morphological distribution and translocation,wheat plant growth and photosynthetic dynamic changes as well as yield.The main results are as follows:?1?Through the lab analysis,the four organic materials contained hydroxyl groups,carboxyl groups and other functional groups,which could effectively adsorb Pb²⁺,but their adsorption properties were different.In the range of pH1.0⁶.0,the adsorption capacity of straw,chicken manure and biochar was influenced by pH value dramatically,and their optimum pH was 5.0,the optimum pH for mushroom cultivating residue was 2.0,and pH value had less effect on the its adsorption capacity of Pb²⁺,as the adsorption capacity decreased smoothly when pH increased.Under the condition of 25 ?and pH5.0,the adsorption equilibrium of the four materials could be reached quickly,and the adsorption process could be well fitted by pseudo-second-order kinetic model and Langmuir isotherm equation,in which the equilibrium adsorption capacity of biochar was much higher than that of the others and reached 411.52 mg·g-1,while the maximum adsorption capacity of straw,chicken manure and mushroom cultivating residue was 40.90,41.82,115.65 mg·g-1 respectively.?2?Soil pH decreased with the addition of 600 mg·kg-1 Pb,and decreased even more in the wintering period and maturity,while the content of organic matter and soil cation exchange capacity increased to a certain extent.The addition of straw or chicken manure had the tendency to decrease the pH value of soil,and the addition of mushroom cultivating residue or biochar could significantly increase soil pH and promote the organic matter content.Besides,the addition of mushroom cultivating residue had a positive effect on the cation exchange capacity of soil.?3?After addition of 600 mg·kg-1 Pb,the content of different forms of Pb in soil was increased significantly.The application of straw and chicken manure in Pb polluted soil has increased the content and proportion of DTPA extractable,exchangeable as well as reducible lead in soil.The treatment of adding mushroom cultivating residue to Pb contaminated soil had the lowest content and proportion of DTPA extractable,exchangeable and reducible lead,while increased the content and proportion of residual lead.The content of DTPA extractable lead in soil showed no significant change after adding biochar,while the content and proportion of oxidizable and residual form of lead had been raised.?4?While the lead content and the translocation and enrichment coefficients of different treatments were different,the addition of organic materials didn't increase the content of lead in the edible parts of wheat,and the addition of mushroom cultivating residue or biochar reduced the lead content in wheat grain at maturity.?5?After adding 600 mg·kg-1Pb,the abundance and diversity of bacterial OTUs in soil was decreased,while the relative abundance of actinomycetes was increased.The abundance and diversity of fungal OTUs was also increased,in which the relative abundance of Ciliophora was decreased while that of Ascomycotawas had been increased.After the addition of chicken manure,mushroom cultivating residue or biochar,the total number of bacterial species in contaminated soil had been increased,in which the relative abundance of Actinomycetes was decreased.As for fungus,the addition of straw,chicken manure or biochar reduced the total number of fungal species in the contaminated soil,while the mushroom cultivating residue showed an enhancement effect.The addition of these organic materials all increased the species diversity of fungi,in which the relative abundance of Ascomycota was decreased while the relative abundance of Ciliophora,Chytridiomycota and Zygomycota was increased,and the effect of chicken manure,mushroom cultivating residue and biochar was more obvious.?6?After adding 600 mg·kg-1Pb,the growth of wheat at wintering period was promoted,butits biomass accumulation and yield traits at maturity was inhibited significantly.Additionally,the remediation effect of different organic materials on Pb contaminated soil was different.Biochar promoted the net photosynthetic rate of wheat leaves at 15 d and 30 d after anthesis,and mushroom cultivating residue had a positive effect on root elongation.Furthermore,the biomass accumulation was increased and the yield traits at maturity of wheat were optimized with adding chicken manure,mushroom cultivating residue or biochar,while the treatment of adding straw did not alleviate the stress of lead on the biomass accumulation and yield of wheat.