二维电场对土壤中镉活化和迁移以及对伴矿景天生长和吸收镉的影响机制研究

Sedum plumbizincicola, as a Cd/Zn hyperaccumulator, is widely used in remediation of Cd contaminated farmland. However, because of its shallow roots, it can only enrich heavy metals with high availability within the reach of roots. Two-dimensional (2D) electric field can deliver heavy metals from deep soil to plant roots and enhance plant uptake of heavy metals in soil, but the effect and mechanism of 2D electric field on growth and Cd uptake of Sedum plumbizincicola is not clear. This study is proposed to use 2D electric field which refers to the use of vertical anode in four corners of soil matrix and horizontal cathode on the soil surface, select cadmium hyperaccumulator Sedum plumbizincicola as the experimental plant, adopt pot experiment, using chemical methods, synchrotron radiation techniques (μ-XRF and XAS) and plant physiological methods, to study the effect of 2D electric field with different intensities on soil properties, nutrient content and total and available Cd content in soil, the changes of physiological and biochemical indexes such as chlorophyll content, key enzymes activity and root morphology and activity as well as the in vivo Cd distribution and speciation in root will be analyzed to reveal the mechanism of 2D electric field on Cd migration and the growth and Cd uptake of Sedum plumbizincicola. Finally, the applicability of the combined technology under different conditions such as different soil types and different current conditions will be discussed. The results of this study will provide theoretical basis and technical support for the application of the coupled phytoremediation-electrokinetic technology.

伴矿景天作为一种镉锌超积累植物，在我国镉污染农田修复中应用广泛。但由于其根系较浅，仅能富集根际范围内有效性较高的重金属。二维电场可使土壤深处重金属向植物根部迁移，增强植物对重金属的吸收，但其对伴矿景天生长和吸收镉的影响程度及机理并不清楚。本项目拟采用二维电场（垂直阳极在四周，水平阴极在土壤表面），以镉超积累植物伴矿景天为研究对象，通过盆栽试验，应用化学方法、同步辐射技术和植物生理手段，研究不同强度二维电场对土壤性质、养分离子含量、土壤中镉浓度及有效性的影响；分析伴矿景天叶绿素含量、关键酶活性及根系形态和活力等生理生化指标的变化，与镉在伴矿景天根系的原位分布特征和赋存形态相结合，揭示二维电场对土壤中镉迁移及伴矿景天生长和吸收镉的影响机制；最后探讨二维电场-伴矿景天联合修复技术在不同土壤类型、不同通电条件下的适用性。该研究结果将为电动-植物联合修复技术的应用提供理论依据和技术支持。

针对伴矿景天根系较浅，仅能富集根际范围内有效性较高的重金属的问题，本研究通过构建二维电场，研究了不同强度二维电场以及与不同增强试剂相结合对土壤中镉迁移转化以及对伴矿景天生长和吸收镉的影响。本研究取得的主要研究成果如下：.（1）构建了垂直石墨棒状阳极在四周，水平不锈钢网状阴极在土壤表面的二维电场，研究了不同强度二维电场对土壤中镉迁移转化和伴矿景天生长和吸收镉的影响。结果表明，15 V电压可促进镉从底层迁移至表层土壤，增加底层和中层土壤中镉的有效性，使表层土壤镉有效性略有降低。但高强度电场严重抑制了伴矿景天生长，降低了植物叶绿素含量，提高试验后期叶片伤害率，严重破坏植物根细胞结构，进而抑制了伴矿景天对镉的吸收。5 V电压对伴矿景天生长无显著性影响，但因降低了表层土壤镉有效性，未提高伴矿景天对Cd的积累。10 V电压对植物生长的影响为先刺激后抑制，表明通电时间在电动-植物修复系统中起着决定性作用。因此，有必要选择合适的电极布置、电场强度和通电时间以实现EKPR系统中植物提取效率的提高。.（2）为了减少水平阴极对土壤镉有效性和伴矿景天生长的负面影响，构建了棒状石墨阳极在四周，垂直网状不锈钢阴极在土壤表层的二维电场，同时研究了硫粉、菌菇渣溶解性有机质（DOM）和柠檬酸及固定直流电场和反转电场对土壤理化性质、镉迁移转化、伴矿景天生长和镉吸收的影响。结果表明：施加硫粉显著提高了伴矿景天根部对镉的积累，但显著降低了伴矿景天地上部生物量和地上部镉积累量；施加DOM和柠檬酸可显著促进伴矿景天生长和Cd积累量。施加固定直流电场使土壤表层总镉发生迁移，增加了植物根区土壤总镉含量，但并未使底层土壤总镉向表层土壤迁移。反转电场使表层土壤总Cd向底层迁移。固定直流电场相对反转电场可增加植物对Cd的吸收，反转电场相对固定直流电场能增加植物生物量。在利用伴矿景天修复碱性污染土壤时，电场+硫粉处理可作为一种有效的强化措施，但硫粉的施用量需进一步优化。