| Heavy metal pollution has become a major ecological and environmental problemthat threatens food safety,affects human health and impedes the sustainable development of agriculture.In recent years,it has become a social focus of public concern,and also a research hotspot in the fields of soil and environmental science.Soil is a multi-phase system and is composed of minerals,organic matter and microorganisms.The complex interaction among soil components significantly affects the distribution,mobility,transformation and availability of heavy metals in soil.Relevant research is the basis and key for soil risk assessment and pollution remediation.In this study,a 3-years incubation was conducted to study the speciation of Cu and Pb in Ultisol,Alfisol and Histosol.Using sequential extraction,nuclear magnetic resonance,nano-secondary ion mass spectrometry,synchrotron radiation infrared spectroscopy,synchrotron radiation soft X-ray spectroscopy and synchrotron radiation X-ray fluorescence,1)we explored the regulation and influential factors of Cu and Pb in threes soils with aging,2)we investigated the effects of organic matter and microorganisms on the speciation and distribution of heavy metals in soils,3)we evaluated the distribution of heavy metals on different sized aggregates,4)we also studied the effects of temperatures on the stablization and transformation of organic carbon at soil microinterface.The main results and conclusions are as follows:（1）The speciation and controlling factors of Cu and Pb were elucidated during aging.After 36-month incubation,the proportion of specifically adsorbed Cu and Pb decreased by 52%-70%,while that of residual Cu and Pb increased significantly in three soils.The proportion of iron-manganese oxides Cu increased by 47%-74%,and that of Pb increased by 24%-109%.No significant changes were obtained for other forms of Cu and Pb.Obviously,aging promoted the transformation of Cu and Pb from specifically adsorbed to iron-manganese oxides bound and residual species.Based on multivariate stepwise linear regression analysis of soil properties and mobility factor of Cu and Pb,we found that the mobility of Cu and Pb is mainly controlled by soil organic carbon,amorphous iron oxide and p H for Ultisol,Alfisol and Histosol,respectively.（2）The effects of straw and straw+engineering bacteria on the speciation and transformation of exogenous Cu and Pb in three soils were clarified.After adding straw and straw+engineering bacteria,the proportions of specifically adsorbed Cu and exchangeable Pb decreased by 23%-34%and 56%-76%,respectively,while humic substance-bound Cu and Pb increased by 14%-106%in Ultisol.For Alfisol,the proportion of specifically adsorbed Cu and exchangeable Pb decreased by 10%-37%and 2%-11%,while humic substance-bound Cu and Pb increased by 3%-31%.For Histosol,the contents of specifically adsorbed Cu and exchangeable Pb decreased by15%-38%and 4%-27%,respectively,while humic substance-bound Cu and Pb increased by 2%-42%.No remarkable changes were obtained for other forms of Cu and Pb.Clearly,addition organic matter and microorganisms mainly promoted the transformation of specially adsorbed Cu and exchangeable Pb to humic acid bound forms in three soils.（3）First investigation on the distribution of Cu in Ultisol of different sized aggregates by Nano SIMS.After 28 months aging,the correlations between Cu and C in the<2μm and 20-63μm aggregates increased from 0.25 to 0.46 and 0.43,respectively,while the correlations between Cu and Fe/Al decreased from 0.43-0.50and 0.17-0.32 to 0.29-0.32 and 0.06-0.25,indicating that Cu tended to bind to organic components in these two aggregates.The organic function groups bound to Cu in these aggregates are remarkablely different.In the<2μm aggregates,Cu is mainly related to carboxyl carbon,while it is better related to alkyl carbon in the 20-63μm aggregates,indicating that carboxyl and alkyl carbon control the distribution of Cu in in these two aggregates.（4）The accumulation characteristics of Cu in Histosol of the<2μm soil aggregates were evaluated.After 28 months aging,the correlations between Cu and Fe/Al/Mn in the<2μm aggregates increased from 0.10-0.17 to 0.55-0.63,while the correlations between Cu and C decreased sharply from 0.61 at month 4 to 0.10 at month 12,and increased to 0.36 at month 28,indicating that Cu tended to be enriched in inorganic mineral components in the<2μm aggregates of Histosol.The relative content of aromatic and carboxyl carbon decreased from 8.1%and 30.8%to 3.6%and17.8%at month 4 to 12,respectively,and increased to 5.9%and 26.0%at month 28.Alkyl and carbonyl carbon increased and then decreased during aging.The consistency of the correlations between Cu and C with the changes of aromatic and carboxyl carbon indicated that aromatic and carboxyl carbon play a key role in organic component bound Cu in the smallest aggregates of Histosol.（5）The effect of temperature changes on soil iron oxides bound organic carbon was clarified.Warming decreased the total organic carbon content from 18.82 g kg-1to 14.56 g kg-1 and 40.38 g kg-1 to 32.91 g kg-1 in Ultisol and Histosol,respectively,with a decrease of 23%and 18%.At the same time,the content of iron oxides bound organic carbon decreased from 3.46 g kg-1 to 1.99 g kg-1 in Ultisol,and increased that from 4.04 g kg-1 to 5.12 g kg-1 in Histosol.Warming promoted the associations of organic carbon with iron oxides by adsorption in Ultisol,while coprecipitation played an important role in the associations of organic carbon with iron oxides in Histosol.The nuclear magnetic resonance（NMR）results suggested that warming could alter the composition of soil organic matter at the molecular level,accelerating O-alkyl C degradation and increasing recalcitrant alkyl C and carboxyl C sequestration.Comprehensive studies of C/N,13C isotope and synchrotron radiation-based fourier transform infrared（SR-FTIR）spectroscopy indicated that warming promoted iron oxides to selectively stabilize microbial-derived polysaccharides and aliphatic compounds. |
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