超富集植物对稀土元素的吸收、转运和分馏机制

Rare earth is one of the most important strategic resources in the world. However, the traditional mining technology for the ionic rare earth mine in south China has led to severe ecological degradation in the mine area, and more importantly, has resulted in a great loss in the amount of rare earth in tailings. In this case, phytoremediation using rare earth element (REE) hyperaccumulators, offers a cost-effective solution to achieve the goals of both soil pollution control and REE recycling from the tailings. By using the light REE hyperaccumulator Dicranopteris dicthotoma and the heavy REE hyperaccumulator Phytolacca americana L. as testing plant materials, this project aims at studying transfer and fate of REEs within the rhizospheric soil solution-root-shoot system and their associated fractionation patterns. More specifically, (1) the ion exchange resin and the dialysis tubing approaches will be used to determine the bioavailability of REEs in the rhizospheric soil; (2) the root and its protoplast will be separated to clarify the transport pathways across the root cell membranes and quantify the contribution of apoplast and symplast transport to the root REE uptake; (3) the xylem sap will be collected for the measurement of REE speciation in order to reveal the mechanisms of REE translocation and the role of organic ligands; (4) the SEM-EDS and EXAFS techniques will be used to explore the cellular distribution and storage forms of REEs in the leaves. Overall, these above studies concerning the key processes of REE transfer associated with their REE fractionation patterns will help to uncover the underlying mechanisms of REE uptake, translocation and sequestration in the hyperaccumulators, hence providing a scientific support for remediation of the ionic REE mine tailings.

稀土是世界上极为重要的战略资源，而我国传统落后的采矿工艺，导致南方离子型稀土矿区生态破坏严重，更造成大量尾矿稀土资源废弃。利用超富集植物开展植物修复机理研究，有助于实现污染治理和尾矿稀土资源化的双重目标。项目以轻稀土超富集植物芒萁(Dicranopteris dicthotoma)和重稀土超富集植物美洲商陆(Phytolacca americana L.)为材料，系统研究稀土在根际土壤溶液-根系-地上部体系中的迁移和分馏机制。拟采用离子交换树脂和膜透析法，研究植物利用稀土的生物有效形态；通过原生质体分离和跨膜吸收动力学，阐明根系稀土的运输路径并定量质外体和共质体吸收的贡献；提取木质部伤流液分析其稀土形态，明确根向地上转运稀土的机制及有机配体的作用；利用电镜和同步辐射技术探究稀土在叶片中的亚细胞分布和贮存形态；结合以上过程中产生的稀土元素分馏参数，揭示超富集植物对稀土的吸收、转运和贮存机制。

相对于超富集植物对锌/镉/镍/砷等重金属的富集机制，超富集植物对稀土的吸收、转运和解毒机制还很不清楚。本项目以稀土超富集植物芒萁和美洲商陆为研究对象，系统研究从土壤根际到植物体内迁移路径中各种生物化学过程对稀土形态及分馏特征的影响，揭示超富集植物对稀土的吸收转运和富集机制。主要结果如下：.(1) 芒萁是一种轻稀土、铝和硅的超富集植物，其对稀土的富集受土壤总稀土、提取态稀土和磷含量的影响；美洲商陆则是一种铝、锰和重稀土的超富集植物，其对稀土的富集量主要受到土壤磷的调控；.(2) 芒萁和美洲商陆对稀土的吸收转运是一个主动耗能的过程，且外源添加铝、锰和钙都能显著抑制其对稀土的富集。从芒萁根系中克隆得到一种水稻OsNrat1的同源基因DlNRAMP，通过酵母和拟南芥体系验证，发现DlNRAMP具有跨膜运输稀土的功能；.(3) 矿区和非矿区芒萁木质部汁液中几乎100％稀土都以REEH3SiO42+存在，而铝主要与柠檬酸结合，部分以AlH3SiO42+存在，表明硅在稀土木质部转运中起着重要作用。而稀土处理下，美洲商陆木质部汁液柠檬酸含量显著增加，软件模拟进一步发现稀土主要与柠檬酸结合；.(4) 通过一系列原位表征手段，发现芒萁主要将稀土区隔在叶片坏死组织、上表皮和叶脉中柱鞘等生物非活性组织，进一步通过扫描电镜观测和化学提取，明确了与硅共沉淀是芒萁叶片中高浓度稀土主要的解毒方式。.(5) 此外，本项目还通过稀土分馏模式、铈和铕异常分析，发现离子型稀土矿尾砂地中稀土淋溶活动强烈，从而造成周边河流、沉积物和农田土壤严重的稀土污染；基于超富集植物、耐性植物和麻类经济作物对稀土的高效吸收或阻隔机制，研发了以稀土植物提取和植物稳定为主的稀土矿山土壤修复技术；基于热解-冷凝技术以及浸出-除杂-沉淀条件优化，开发了一整套回收超富集植物中稀土和能源的方法和设备，为稀土矿区生态修复提供了理论基础和技术支撑。