污染稻田水分管理对水稻吸收积累镉的影响及其作用机理

The effect of water management on the mechanism and rate of uptake and accumulation of cadmium by rice growing in polluted paddy soil

Cd污染稻田通过长期淹水灌溉能显著降低稻米中Cd含量。利用Cd污染水稻土的盆栽试验,结合水稻根表氧化铁膜特征的分析,研究了不同水分管理对水稻吸收积累镉的影响及其作用机理。结果表明,随着稻田淹水程度(时间和水量)的提高,水稻根表氧化铁膜所吸附的还原态Fe(Ⅱ)、Mn(Ⅱ)显著增加,潮泥田和黄泥田长期淹水灌溉处理的水稻根膜中的Fe(Ⅱ)分别比湿润灌溉处理增加了12.6倍(p<0.01)和8.5倍(p<0.01);不同水分管理的水稻根膜氧化铁(Fe(Ⅲ))含量的变化与根膜Fe(Ⅱ)表现极显著的相关性,但两者均与水稻根膜Cd呈极显著的负相关,其中,2种土壤长期淹水的水稻根膜Fe(Ⅲ)分别比湿润灌溉增加了1.5倍(p<0.01)和1.0倍(p<0.01),根膜吸附的Cd含量分别较湿润灌溉降低了77.9%(p<0.01)和50.3%(p<0.01);长期淹水处理导致水稻根系、茎叶、糙米中的Cd含量均极显著低于相应的湿润灌溉处理,2种土壤长期淹水的糙米平均Cd含量比间歇灌溉的下降了41.3%,比湿润灌溉的下降了70.7%(p<0.01);不同水分管理的水稻糙米Cd含量与根膜Cd含量呈极显著正相关,与根膜Fe(Ⅱ)和Fe(Ⅲ)呈极显著负相关。综合分析认为,Cd污染酸性稻田在长期淹水的还原条件下Fe2+等金属离子与Cd2+的竞争吸附作用以及S2-和Cd2+的共沉淀作用加强,因而使得土壤中Cd的生物有效性明显降低。

Irrigation by continuous flooding could result in a distinct decrease in the cadmium （Cd） content of brown rice grown in paddy soil polluted by cadmium. The effect of water management on the mechanism and rate of uptake and accumulation of cadmium by rice was studied using rice pot experiments combined with analysis of the characteristics of membrane coated outside the roots of riee growing in two types of paddy soils polluted by cadmium in Hunan Province in 2005. The results showed the amount of Fe （ Ⅱ ） and Mn （ Ⅱ ） absorbed by the root coating of riee increased with the duration of flooding and the depth of water in the paddy soils. The Fe （ Ⅱ ） contents of the root coating of riee grown in Alluvial Loamy Paddy Soil （ALPS） and Yellow Clayey Paddy Soil （YCPS） irrigated by continuous flooding （FI） treatments were increased by 12.6 times （p 〈0. 01 ） and 8.5 times （p 〈0. 01 ）, respectively, compared with corresponding controlled moisture irrigation （CI） treatments. Correlation analysis revealed significant linear relationships between the content of ferric oxides Fe （Ⅲ ） and ferrous Fe （ Ⅱ ） in the rice root coating for the different water management treatments. The Fe（ Ⅲ ） content in the root coating of rice grown in the two types of paddy soils with the FI treatments increased by 1. 5 times contents 50.3% resulted （p 〈0.01 ） and 1.0 times （p 〈0.01 ）, respectively, compared with the corresponding CI treatments. The cadmium in the root coating from the two types of paddy soils with the FI treatments decreased by 77.9% （p 〈0. 01 ） and （p 〈 0. 01 ）, respectively, compared with the corresponding CI treatments. The different irrigation treatments in a strong negative relationship between the content of cadmium and that of both Fe（ Ⅱ ） and Fe（ Ⅲ ） in the root coating of rice. Compared to the CI treatments, the FI treatments in paddy soils also resulted in distinctly lower cadmium contents in the roots, straw and brown rice. The average cadmium contents in brown riee grown on the two paddy soils with FI treatments were decreased by 41.3% compared with the intermittent irrigation （Ⅱ） treatments, and were decreased by 70.7% （p 〈 0.01 ） compared with the CI treatments. The cadmium content in the brown rice had a strong positive relationship with the cadmium content in root coating, but a remarkably negative relationship with ferric oxides in root coating for all water management regimes. Conclusively, we deduced that the competitive adsorption of metal cations like Fe^2＋ with Cd^2＋ , and the co-sedimentation of S^2- and Cd^2＋ increased greatly under the reductive condition of the continuous flooding irrigation water in acid paddy soil polluted by cadmium, which significantly reduced the bio-availability of cadmium in the soils.