Experimental Study On Migration Characteristics And Ecological Effects Of Heavy Metals In Oasis Soil-Carrots System In Arid Regions

The migration characteristics study of four heavy metal elements in the arid oasis soil-vegetable system are still insufficient.In this thesis,a pot experiments were carried out to study the characteristics of migrants of Cd,Pb,Zn,Ni in the arid oasis soil-carrot system and its ecological effect.The study results showed that:(1)Contents of various species of soil Cd,Pb,Zn,Ni increased with increasing exogenous metals concentrations.At the same time,the various species of heavy metals in soil were redistributed.The exchangeable form and carbonate bounded form had the greatest response and residual form had the least response when the exogenous Cd,Pb,Zn and Ni were added jointly.With the increasing concentration of exogenous heavy metals,the main chemical speciation of Cd changed from residual form into exchangeable form gradually,while the main chemical speciation of Pb changed from residual form into carbonate bounded form and ferric-manganese oxide rapidly,and the main chemical speciation of Zn and Ni changed from residual form into ferric-manganese oxide.(2)Compared with control group,the heavy metals content of carrot tuber and stem leaves(except Pb content in the stem leaves)were increased with the addition of exogenous metals.Overall,the enrichment ability of Carrot tuber to Cd,Pb,Zn,Ni was Cd>Zn?Ni>Pb,and the enrichment ability of Carrot stem leaves to Cd,Pb,Zn,Ni was Cd>Zn>Ni>Pb.Cd,Pb,Zn,Ni migrational ability in Carrot was Zn>Cd>Ni?Pb in low(TS1,TS2)additive concentration,while in middle and high(TS3?TS6)additive concentration,the order of migrational ability was Cd>Zn>Ni>Pb.(3)Through multiple linear regression analysis,it was showed that differences of heavy metals transfer ability to the carrot tuber and stemleaf was resulted in the complex interaction between the heavy metals in soil with Cd,Pb,Zn,Ni compound pollution condition.Through multiple stepwise regression analysis,it was showed that the main contribution form of uptake of Cd and Zn by carrot tuber was carbonate bounded form,and the main contribution form of uptake of Pb and Ni by carrot tuber was exchangeable form.The main contribution form of uptake of Cd,Zn and Ni by stem leaves was carbonate bounded form,and the main contribution form of uptake of Pb by stem leaves was exchangeable form.This shows that the exchangeable form and carbonate bounded form of heavy metals in soil easily absorbed by the carrots.(4)The inhibition rate of some carrot's growth indications all showed a increasing trend with the increase of compound heavy metals(Cd,Pb,zinc,Ni)concentration,and the order of different growth indice's inhibition rate organ was tuber dry weight>stem leaves dry weight>tuber length>stem leaves length.It showed that effect of toxicity on the tuber dry weight was strong,followed by the stem and leaf dry weight,the length of the stems and leaves and tubers length were relatively weak.The order of different growth indice's resistance coefficient was stem leaves length>tuber length>stem leaves dry weight>tuber dry weight.This illustrates carrot m leaves length has the strongest tolerance,followed by the length of the stems and leaves,tubers dry weight and stem leaf dry weight were relatively weak.