Influence Of Sulfur On The Formation Of Fe-Mn Plaque On Root And Uptake Of Cd By Rice(Oryza.sativa L.)

A pool culture experiment using exogenous Cd-polluted paddy soils was carried out to investigate the influence of different forms of sulfur fertilizers(sulfur and gypsum) on the formation of Fe-Mn plaque on rice root, the uptake of Cd by rice and the mass fractions of different speciation Cd in soil. The results showed as follows:1. The redox potential(Eh) of Cd-contaminated soil solution was about- 200- 100 m V,the p H was 6.9- 7.9 and the pe + p H was 4- 10 in different growth periods of rice. There was little significant influence on the redox potential(Eh) and the pe + p H after being Cd contaminated, while the p H average value increased.2. Fe plaque was confirmed to dominate Fe-Mn cutan on rice root at different growth stages of rice. The Cd-contaminated mass fractions of Fe and Mn plaque on rice root were5000- 13000 mg·kg-1 and 170- 580 mg·kg-1, respectively. The high sulfur treatment led to the formation of more Fe plaque than the low sulfur treatment, and the mass fractions of Fe plaque in both treatments were 9400 mg·kg-1 and 8600 mg·kg-1 respectively in the boot stage.Contents of Mn plaque, significantly different in the tiller stage by elemental sulfur treatment and gypsum treatment, were 600 mg·kg-1 and 400 mg·kg-1, respectively. The elemental S treatment led to the formation of more Mn plaque on rice root than the gypsum treatment.Uncontaminated rice had the same situation.3. The excessive intake of Fe2+ might be prevented by the formation of the plaque which had little significant influence on the uptake of Mn2+.4. The mass fractions of Cd adsorbed by rice roots surface plaque were 78.8- 131.1mg·kg-1 in tiller stage, 16.6- 21.1 mg·kg-1 in boot stage, and 3.0- 9.2 mg·kg-1 in mature stage.The high sulfur treatment led to higher adsorption of Cd by the plaque than the low sulfur treatment in the tiller stage and the boot stage, while opposite result was observed in the mature stage. The values of Cd on the plaque measured by ACA could not truly show its actual contents adsorbed.5. The mass fractions of Cd in the different parts of rice followed the order of roots >stem leaf > grain. The sulfur fertilizers applied significantly reduced the mass fractions of Cd uptake in different parts of rice, and the elemental sulfur treatment had better effects than thegypsum treatment before the mature stage in roots and stem leaf, and the gypsum sulfur treatment was better for grain.6. A certain amount of sulfur fertilizers could effectively prevent the migration of Cd from roots to stem and grain. The transfer coefficient of Cd from roots to stem leaf in the elemental sulfur treatment and the gypsum treatment were 0.13 and 0.25 in the boot stage,respectively, and the difference was significant. Elemental sulfur was more effective to prevent the Cd migration from roots to stem leaf, and the gypsum treatment was more active from roots to grain.7. The bioavailability of Cd in rhizosphere soil was lower than non-rhizosphere soil.S-fertilizer could effectively reduce the mass fractions of exchangeable-Cd and its percentage.The high sulfur treatment had more significant influence than the low sulfur treatment.Gypsum sulfur treatment was more active to reduce the bioavailability of Cd in soil.