外源铁对水稻吸收土壤砷的影响及其机理

Arsenic (As) is a poisonous element. Soil As in contaminated area can be uptake by straw and rice, and endanger human health through food chain. Therefore, how to reduce arsenic uptake by and translocation within rice plants is a big problem that require being solved immediately. It is difficult to control As transportation from soil to rice plants due to the special fractionations of As in the soil. However, the previous researches showed that the material containing iron could stabilize As in soil environment. Moreover, the Fe plaque could appear around root rhizosphere, and hold-up As entering into the root system. Therefore, the exogenous Fe may be a promising chemical immobilizer to reduce As uptake by rice plants in As-contaminated soil. Rhizo-bag cultivated system will be used to investigate the effects of different amount of exogenous Fe on rice plants growth and arsenic uptake by rice plants in greenhouse. The stabilization of As in soil, the induction of Fe plaque on root, and the influence of root Fe plaque on As accumulation by rice root will be analyzed to discuss the mechanisms of exogenous Fe reducing As uptake by rice plants. Finally, the effects of the increasing soil pH and the root secretion on As accumulation and translocation in rice after application of exogenous Fe will be studied to assess the stability and persistent of the function of exogenous Fe. The aim of project is explore the remediation technology of As contaminated field.

砷（As）是一种剧毒元素，污染稻田中的As可通过秸秆和稻米经食物链危害人体健康，因此在污染地区控制As向水稻转移是一个亟待解决的问题。As在土壤中的存在形态不同于重金属，其迁移控制是非常棘手的事情。现有的研究表明，含铁（Fe）材料对环境介质中的As有一定的固定作用；此外，水稻也能利用根际环境中的Fe形成根表Fe膜，阻碍As进入根系。因此，稻田中外源Fe的加入有望减少水稻对As的吸收。本项目采用土壤-玻璃珠联合培养的方法，研究As污染土壤中施用不同量的外源Fe对水稻生长与As吸收的影响效应；并通过分析外源Fe对土壤As的吸附固定，对水稻根表Fe膜形成的诱导，以及根表Fe膜形成对As进入水稻根系的影响，来探讨外源Fe作用的机理；最后研究土壤pH提高和根系分泌物出现对外源Fe影响As迁移的干扰，评价外源Fe作用的稳定性。这些研究工作旨在探索As污染稻田治理的技术和理论。

As是一种剧毒元素，污染稻田中的As可通过秸秆和稻米经食物链危害人体健康，在污染土壤中控制As向水稻转移是一个亟待解决的问题。项目组通过水稻盆栽试验研究施用外源Fe对水稻吸收土壤As的影响及机理，并对外源Fe作用的稳定性进行了探讨和评价，研究工作为As污染稻田的治理提供了理论和技术支持。结果表明，（1）在FeCl3、FeCl2、Fe0 和Fe2O3都能明显降低土壤中易溶态和毒性浸出As含量，Fe0对土壤性质影响较小，是较理想的As污染土壤修复材料。（2）Fe0显著地降低了根、壳、糙米中总As和无机As含量。在最大添加量8.00 g/kg时，与对照相比，根、壳、米中总As分别降低了54.85%、39.86%和30.07%，无机As分别降低了59.23%、30.82%和30.26%。（3）从形态方面解释，Fe0固定土壤As的机理主要是Fe0在土壤中转化为无定形Fe、碳酸盐结合态Fe、氧化锰结合态Fe等能强吸附As或与As共沉淀的形态Fe，与土壤中WE-As，Al-As，Fe-As反应，使其主要向稳定性强的RS-As转化。（4）添加FeCl3能有效地降低土壤As的生物有效性，但提高了土壤重金属的生物有效性。（5）Fe0在整个水稻生育期内均降低了土壤WE-As、Al-As、Fe-As含量，增加了土壤RS-As含量，且种植前和收获后降低WE-As和增加RS-As的效果相当，其固As效果在一个水稻生育周期内具有良好的持久性。（6）DSP和HAP均显著降低了水稻根总As、糙米总As、糙米无机As含量，但HAP显著增加了水稻茎叶总As含量。DSP降低糙米中总As和无机As的效果与HAP相当。水稻各器官中As含量受到2种相反作用影响：一、水稻体内P-As拮抗作用抑制As在水稻中的迁移转运；二、含P物质增加A-As，降低R-As，促使土壤As的迁移能力和生物可利用性增强。本试验条件下，拮抗作用占主导地位，并在根、糙米这两个部位中有明显体现。（7）A⁃F处理能显著降低水稻根和茎叶As含量，FA和AFA处理都能显著降低水稻茎叶、谷壳、糙米As含量和糙米无机As含量。F-A和AFA处理降低糙米As含量的机理是，灌浆期是水稻糙米吸收土壤As的关键时期，此时的湿润灌溉提高了土壤Eh，土壤溶液3价As和5价As浓度之和以及3价As/5价As显著降低，从而使土壤As的迁移能力得到抑制。