Reversible reduction-oxidation processes during the transformation of iron-containing minerals in rhizosphere soils

拟议的研究将导致发现微生物和植物用来影响土壤系统中矿物质中电子进出运动的机制。这些知识对于农业/林业和环境土壤动态特性的管理是重要的。我们最近的研究结果表明，在植物根系和根际土壤微生物（或土壤粘附在根系上）的共同作用下，含铁黑云母和坡缕石类土壤矿物的蚀变产生了新的粘土。当电子从黑云母中失去时，就会合成新的矿物，而当坡缕石结构中的铁接受电子时，就会导致另一种矿物的结晶。目标-总的来说，目的是了解土壤矿物质的转变，并发现应用这些知识来保护土壤养分以促进植物生长和恢复因开采矿石、石油、天然气和其他自然资源而退化的土地的方法。我们想要确定细菌的作用，单独或与真菌和植物结合，在移动电子在土壤矿物质，以及在铬污染的土壤解毒。有毒的六价铬在其结构中加入电子后变成无害的三价铬。土壤是高活性物质，含有多种电子源/汇，包括硫和含铁矿物。科学方法-我们将在实验中使用零价铁材料和以下矿物作为电子的源/槽：黑云母，坡缕石，蒙脱石，绿泥石来评估真菌（例如，褐皮菌）和细菌菌株（例如，氧化亚铁酸硫杆菌）与农作物结合的作用，以研究土壤系统内的电子流动。电感耦合等离子体质谱将用于表征根际样品的无机和有机成分，而分子DNA测序技术将用于描述土壤生物。x射线和电子显微镜将用于收集有关新矿物的化学和晶体信息。同步辐射——一种非常强大的能量，通过弯曲非常快的（加速）电子的方向产生，将用于在电子获得或失去之前和之后引起矿物中铁结构的变化。使用同步辐射的一些好处包括非常少的样品制备和它在非常少量的样品（几毫克）上工作的能力。我们利用加拿大光源（加拿大唯一的同步加速器设施）的同步加速器（VESPERS）光束线辐射获得非常敏感的元素和结构探测器，在过去四年中一直在持续，并预计至少在未来五年继续。来自加拿大和国外的合作者（例如École Normale supsamrieure，法国）将进行专门分析，例如各种粘土矿物的定量和土壤生物的鉴定。预期意义：新信息将促进对含铁矿物变化过程中电子损失/获得的生物和地球化学机制的认识。根际土壤中新形成的膨胀粘土的一些好处包括必需养分（如钾）和阳离子交换能力（或土壤储存养分的能力）的增加。这些将对加拿大和其他地方的农业和林业有用。在环境应用中，通过从富铁材料中获得电子将铬- vi解毒为铬- iii将在铬污染土壤的修复中具有实际应用。

The proposed research will lead to the discovery of the mechanisms used by microorganisms and plants to influence the movement of electrons in and out of minerals in the soil system. This knowledge is important for the management of the dynamic properties of soils for agriculture/forestry and environment. Our recent findings show that new clays arise from the alteration of iron-containing biotite and palygorskite soil minerals from the combined actions of plant roots and soil microorganisms in rhizosphere (or soil sticking on the roots). New minerals are synthesized when electrons are lost from biotite while palygorskite will lead to the crystallization of another mineral when the iron in its structure accepts electrons. Objectives – In general, the purpose is to understand the transformation of soil minerals and to discover means to apply this knowledge to conserve soil nutrients for plant growth and restoration of degraded lands arising from the extraction of ores, oil, gas and other natural resources. We want to determine the roles of bacteria, alone or in combination with fungus and plants, in moving electrons within the soil minerals, as well as in the detoxification of chromium-polluted soils. Toxic chromium-VI is rendered non-harmful as chromium-III after the addition of electrons into its structure. Soils are highly reactive materials and contain several sources/sinks of electrons including sulfur and iron-containing minerals. Scientific approach - We will use zero valent iron materials and the following minerals as sources/sinks of electrons in our experiments: biotite, palygorskite, smectite, chlorite to evaluate the role of fungus (e.g., Piloderma fallax) and bacterial strains (e.g., Acidothiobacillus ferrooxidans) in combination with agricultural crops to study the flow of electrons within the soil system. Inductively-coupled plasma mass spectroscopy will be used to characterize the inorganic and organic constituents of rhizosphere samples while molecular DNA sequencing techniques will be used to describe the soil organisms. X-ray and electron microscopy will be used to collect chemical and crystal information about the new minerals. Synchrotron radiation – a very powerful energy generated by bending the direction of very fast (accelerated) electrons will be used to cause changes in the structure of iron in minerals before and after the gain or loss of electrons. Some benefits of using synchrotron radiation include the very minimal sample preparation and its ability to work on very small amounts of sample (few milligrams). Our access to the Very Sensitive Elemental and Structural Probe Employing Radiation from a Synchrotron (VESPERS) beamline at the Canadian Light Source, the only synchrotron facility in Canada, has been continuous in the last four years, and is expected to continue for at least the next five years. Collaborators from Canada and abroad (e.g., École Normale Supérieure, France) will conduct specialized analysis such as quantification of various clay minerals and identification of soil organisms. Expected Significance – New information will advance knowledge about the biological and geochemical mechanisms involved in the loss/gain of electrons during the alterations of iron-containing minerals. Some of the benefits from the newly-formed expanding clays in rhizosphere soils include increases in essential nutrients (e.g., potassium) and cation exchange capacity (or the ability of soil to store nutrients). These will be useful to agriculture and forestry in Canada and elsewhere. In environmental applications, the detoxification of chromium-VI to chromium-III by gain of electrons from iron-rich materials will have practical applications for the remediation of chromium-contaminated soils.