Effects of different zinc fertilizers on soil cadmium availability and cadmium uptake and transport in wheat
In this study,we sought to examine the effects of zinc(Zn)fertilizer on cadmium(Cd)absorption and transport by wheat in polluted soil.Pot experiments were conducted to study the effects of different concentrations(13,26 mg·kg-1,and 66 mg·kg-1)and types[conventional zinc fertilizer(CZF)and slow-release zinc fertilizer(SZF)]of Zn fertilizers on Cd and Zn availability in rhizospheric soil and the Cd and Zn uptake and transport in wheat.The results revealed that both types of Zn fertilizer promoted significant increases in the content of soil available Zn,although the availability of Zn in soil at the booting,filling and mature stages of wheat was significantly higher in soil treated with SZF than in CZF-treated soil.The application of CZF and SZF effectively reduced the Cd content in wheat roots at the jointing stage,which was 23%-33%and 3%-48%lower than that of the control,respectively,whereas only medium-and high-concentration CZF and SZF promoted a significant reduction in the root-shoot Cd transfer coefficient.Compared with the control,the application of CZF and SZF effectively reduced the Cd content in the shoots of wheat at the filling and mature stages,with reductions of 21%-54%and 13%-43%,respectively.Although high-concentration SZF significantly(P<0.05)increased the soil available Cd content at the wheat jointing,booting,and filling stages,it promoted a significant reduction(P<0.05)in the root-shoot Cd transfer coefficient at the wheat filling and mature stages.The application of high-concentration CZF also contributed to a significant reduction in the root-shoot Cd transfer coefficient of wheat at the mature stage.In all treatments,only the use of high-concentration CZF and SZF promoted significant reductions(P<0.05)in the Cd content of wheat grains,by 19%and 29%,respectively.Correlation analysis revealed that during the whole growth period of wheat,the Zn content in wheat roots was negatively(P<0.05)correlated with the Cd content in shoots,and that there was a decline in the Cd transfer coefficient from the shoots to grains in response to an increase in Zn concentration,thereby indicating that Zn fertilizers can effectively inhibit the uptake and transport of Cd by wheat.However,the efficiency with which high-concentration Zn fertilizers inhibited the transfer of Cd from the shoots to grains was still low.On the basis of these findings,it is apparent that the application of Zn fertilizer alone to moderately and severely Cd contaminated soil is not sufficient to ensure the safe production of wheat.Accordingly,it will be necessary to combine Zn fertilization with other measures to further reduce the accumulation of Cd in wheat grains at the critical period for Cd absorption by wheat.
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