Immobilization of heavy metals in rhizosphere soils : formulation of phytostabilization technology

制定成功的植物稳定化战略在靶场土壤中，了解重金属是如何固定在根际土壤中的分子水平是至关重要的。本研究的目的是调查i）如何改变铅形态的根际土壤中的各种植物，和ii）铅颗粒在根际土壤中的溶解度和随后对土壤生态系统的影响。采用扩展X射线吸收精细结构（EXAFS）光谱技术和化学提取法研究了5种不同植物根际土壤中铅的形态和溶解度。EXAFS分析表明，Pb主要以PbCO_3的形式存在，吸附在有机质上，吸附在成土水钠锰矿和/或水铁矿上。比较根际和非根际土壤的EXAFS谱，发现根际和非根际土壤的精细结构存在显著差异，表明根际过程对Pb的形态进行了改变。变性梯度凝胶电泳结果表明，污染土壤中的植物生长表现出富集细菌种群的现象，因为根际土壤中的总条带比对照土壤中的条带更亮。pH值在7左右的土壤中细菌多样性增加。

To formulate successful phytostabilization strategies in a shooting range soil, understanding how heavy metals are immobilized at the molecular level in the rhizosphere soil is critical. The objectives of this study were to investigate i) how Pb speciation was modified in the rhizosphere soils of various plant species, and ii) solubility of Pb pellet in rhizosphere and subsequent impacts on soil ecosystems. Lead (Pb) speciation and solubility in rhizosphere soils of five different plant species were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. The EXAFS analysis indicated that Pb occurred as PbCO_3, Pb sorbed to organic matter, and Pb sorbed to pedogenic birnessite and/or ferrihydrite in the bulk soil. Comparison of the EXAFS spectra between bulk and rhizosphere soils demonstrated notable differences in fine structure, indicating that Pb species had been modified by rhizosphere processes. Denatured gradient gel electrophoresis demonstrated that Plant growth in the contaminated soil appeared to enrich bacterial populations since the general band profile exhibited in the rhizosphere soil was brighter than the control soil. Bacterial diversity was enhanced in the soil with the pH value of～7.