Effects Of Distribution Of Particulate Organic Matter On Environmental Behavior Of Heavy Metals In Cultivated Calcareous Soils

POM（Particulate organic matter）is a kind of organic matter with high activity and low humification,which has a significant enrichment effect on heavy metals and has a significant influence on the distribution of heavy metals in contaminated soil.Therefore,it is of great significance to study the interaction of POM（2-1 mm）1,POM（1-0.5）0.5,POM（0.5-0.25）0.25 and POM（0.25-0.053）0.053 with heavy metals in calcareous soil.In this paper,the distribution of POM in calcareous soils and its effect on the environmental behavior of heavy metals were investigated by field investigation and pot simulation experiments.The main research results are as follows:（1）POM0.053 is the main existing form of POM in calcareous soil,and its content gradually decreases with the increase of POM particle size.At the same time,among the four fractions of POM,the total carbon of POM0.053 fraction reached 57.52% of the total carbon in the soil at most.As an important part of the soil carbon pool,POM0.053 fraction contributed to soil carbon fixation and carbon emission reduction.（2）POM in calcareous soil has enrichment effect on cadmium（Cd）and lead（Pb）,among which the enrichment coefficient of Cd in POM1 and Pb in POM0.053 is the largest.Cd and Pb contributed the most to POM0.053 components（mass load）.Ca CO3 and active Ca CO3,as important environmental functional attributes of calcareous soil,play a decisive role in the distribution of heavy metals Cd and Pb in different POM fractions.（3）The addition of organic fertilizer and calcium carbonate significantly increased POM0.053 level content,which reached the maximum when the proportion of organic fertilizer and calcium carbonate was 5% and 25%.p H has been significantly increased under the control measures.The content of Cd in POM was significant,and reached the maximum when the proportion of organic fertilizer and calcium carbonate was 5% and25%,respectively.The contents of Pb in POM0.5,POM0.25 and POM0.053 were also increased.The contents of bioavailable Cd and Pb in POM0.5,POM0.25 and POM0.053 were lower than those in the control group,and reached the minimum when the proportion of organic fertilizer and calcium carbonate were 0% and 25%.Regulation can slow down the accumulation of Cd in wheat grains and roots.Pb has the most obvious inhibition effect on heavy metals in wheat organs.After regulation,Pb content in wheat grains is below the detection limit.In conclusion,POM0.053 is the main occurrence form of POM in cultivated calcareous soil,and it is also the main carbon storage and heavy metal enrichment component of POM in calcareous soil.The distribution of POM was mainly controlled by the proportion of Ca CO3 and active calcium carbonate in soil.Artificial exogenous regulation increased soil organic matter and Ca CO3 levels and inhibited the distribution of heavy metals to soil solutions.