Study On Cd Migration,Transfer And Distribution In Rice Plants

In recent years,the cadmium(Cd)rice incident caused by soil heavy metal pollution has attracted wide attention.Pot experiments and hydroponics experiments were designed in this study.Pot experiments were conducted with Weiyou N0.46(WY46)and Xiangwanxian NO.12(XWX12)as targeted cultivar rice to study the migration,transport and distribution of Cd in rice plants exposited to different Cd contaminated soils(0.5 mg·kg-1 and 1.5 mg·kg-,).In hydroponic experiments,Xiangwanxian No.13(XWX13)was used as experimental cultivar rice to explore the effects of Cd stress on Cd accumulation in brown rice at different growth stages(tillering stage,jointing stage,booting stage,filling stage,dough stage,and maturing stage)of rice plants by adding exogenous Cd(20?g·L-1)at different growth stages,to definite the key growth stages of rice plants for Cd accumulating in brown rice.The main results are as follows:1.Exposited to different Cd contaminated soils,the pH value of rice rhizosphere soil was higher at tillering stage and booting stage than those at filling stage,dough stage stage and maturing stage.The OM and CEC of soil did not change significantly during the whole rice growth period.And the content of CaC12 extracted Cd in WY46 at booting stage was the highest among all of treatments.In the light Cd contaminated soils,the contents of CaC12 extracted Cd in soils of XWX12 changed slightly,while in moderate Cd contaminated soils,the content of CaC12 extracted Cd of XWX12 were relatively high at tillering stage,booting stage and filling stage(0.12,0.17 and 0.11 mg·kg-1).There was a significant positive correlation between soil pH value and soil CEC at different growth stages of rice plant,and there was also a significant positive correlation between soil organic matter and TCLP extracted Cd content.2.In different Cd contaminated soils,the order of Cd content in different parts of rice were root>stem>leaf?ear>husk>brown rice.Furthermore,in the light and moderate Cd contaminated soils,the Cd content in brown rice of WY46 at the maturing stage were lowest,were 0.13 mg kg-1 and 0.35 mg·kg-1,respectively,while for XWX12,the change of Cd content in brown rice between filling stage and maturing stage were maturing stage>dough stage>filling stage.3.The biomass of various rice organs of two cultivar rice showed similar regularity with the extension of growth,and the biomass of rice plants reached the maximum at the filling stage.In light Cd contaminated soils,the Cd accumulation amount of brown rice of WY 46 reached the largest at dough stage(0.34?g·plant-1)and the smallest at maturing stage(0.18?g·plant-1).However,in moderate Cd contaminated soil,the Cd accumulation of brown rice gradually increased with the prolongation of growth period,reaching the maximum(0.63?g·plant-1)at maturing stage.For rice XWX12,the Cd accumulation of brown rice reached the largest at maturing stage(0.46?g plant-1)and the smallest at filling stage(0.07?g plant-1)when it planted in light Cd contaminated soils,while in moderate Cd contaminated soils,the Cd accumulation of brown rice was the largest(0.71?g·plant-1),followed by maturing stage(0.54?g·plant-1)and the smallest(0.08?g plant-1)at filling stage.Pot experiments results suggested that Cd absorbed by rice plants at tillering stage and booting stage were mainly distributed in underground parts,little amount of Cd was transferred to above ground parts(stem,leaf,ear,rice husk and brown rice),contraste with these,at the filling,dough,and maturing stages,the absorbed Cd mainly distributed in the above ground parts,and less Cd accumulated in the roots.4.Hydroponics experiment results revealed that the booting stage,filling stage and maturing stage of rice plants(XWX13)were the important growth stages for Cd accumulating in brown rice,and the relative contribution rates of Cd accumulating in brown rice at these three growth stages were 19.7%,39.3%,and 22.6%,respectively.Therefore,the Cd accumulation in brown rice could be reduced by applying soil amendments at these three stages to obstruct root absorbing or transporting Cd,thus reducing the accumulation of Cd in brown rice.