Inhibitory Of Cd?Pb?Zn Uptake By Rice Plant With Meta-sodium Silicate Amendments

A pot experiment was carried out to study the effects of sodium silicate on the uptake and accumulation of Cadmium(Cd),Lead(Pb),and Zinc(Zn)by three indica rice varieties(Donglian 5,Teyou 009 and Yiyou 673).The main results were as follows:1)Application of sodium silicate increased the effective tillering number,and improved the lodging resistance of rice.Sodium silicate was beneficial to the photosynthesis of rice leaves.After sodium silicate treatment,stomatal conductance and net photosynthetic rate of rice leaves increased slightly while the intercellular concentration of CO2 decreased slightly.At the same time,? PS ? increased slightly,showing that sodium silicate mitigated the damage of the heavy metals on ?PS ?reaction center.2)With the increase of the application rate of sodium silicate,the pH values of the soils and the content of available silicon(Si)were significantly increased whereas the content of available Pb and available Zn decreased significantly.In tillering stage,the pH and the available Si content of the soils were slightly higher than those in the mature stage while the content of available Pb and available Zn in tillering stage was slightly lower than that in mature stage.In the tillering stage,the available Cd of the soils of the three rice varieties was lower than that of the control soil.In the mature stage,the available soil Cd of Yiyou 673 was slightly activated.3)The treatment of sodium silicate increased reducible Cd while decreased residual Cd in the soils.The proportion of oxidizable Pb and residual Pb in the soils was increased whereas that of reducible Pb was lowered.Sodium silicate increased weak acid extractable and reducible Zn but reduced residual Zn in the soils.4)The Si content in the stems and leaves of rice was increased by sodium silicate treatment.The Si content of rice roots in tillering stage increased whereas that in mature stage was slightly decreased by the application of sodium silicate.The Si content in brown rice was not significantly influenced by sodium silicate.The contents of Cd in the various parts of rice were significantly reduced by high rate of sodium silicate.The contents of of Pb in the stems and leaves,and the Zn in the stems were also reduced.5)Sodium silicate enhanced the retention of Cd,Pb,and Zn by iron plaques on the root surface of rice.The transfer of Cd from stem and leaf to rice and the transfer of Zn from stem to rice was promoted,while the transfer of Pb from root to stem and from stem and leaf to rice was inhibited.6)Pb-X-ray absorption near-edge spectroscopic analysis(XANES)showed that the application of sodium silicate decreased water-soluble species of Pb in the soils of Donglian 5,and promoted the formation of adsorbed Pb and precipitated Pb,thus reduced the availability of Pb in root cells.It was found that most Pb existed as precipitated form outside the root cells,resulting in less transfer of Pb into the root cells.7)The effects of sodium silicate on the concentrations of Cd,Pb and Zn in brown rice was different.The application of sodium silicate reduced Cd content in the brown rice of Donglian 5,Pb content in the brown rice of Teyou 009 and Yiyou 67.The content of Zn in the brown rice was somewhat decreased.The highest rate of sodium silicate(12.5 g·kg-1)significantly decreased the contents of Cd,Pb and Zn in the brown rice of the three rice varieties.