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于影响土壤系统中矿物的电子进出运动的机制。 这方面的知识是重要的农业/林业和环境土壤的动态特性的管理。我们最近的研究结果表明，新粘土是植物根系和根际土壤微生物（或根际土壤粘附）共同作用下含铁黑云母和泥炭土矿物蚀变而形成的。 当黑云母失去电子时会合成新的矿物，而当其结构中的铁接受电子时，坡缕石会导致另一种矿物的结晶。 目标-一般而言，目的是了解土壤矿物的转化，并发现如何应用这一知识，为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保持土壤养分。 我们希望确定细菌单独或与真菌和植物结合在土壤矿物质中移动电子以及铬污染土壤解毒中的作用。 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-我们将使用零价铁材料和以下矿物作为我们实验中的电子源/汇：黑云母，坡缕石，蒙皂石，蒙脱石，以评估真菌的作用（例如，毛癣菌）和细菌菌株（例如，氧化亚铁硫杆菌）与农作物相结合，研究土壤系统中的电子流动。 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-通过弯曲非常快（加速）的电子的方向产生的非常强大的能量将用于在获得或失去电子之前和之后引起矿物中铁的结构变化。 使用同步辐射的一些好处包括非常少的样品制备及其对非常少量的样品（几毫克）的工作能力。 我们在加拿大唯一的同步加速器设施-加拿大光源-获得利用同步加速器光束线辐射的非常灵敏的元素和结构探测器的机会，在过去四年中一直在进行，预计至少在今后五年内将继续进行。 来自加拿大和国外的合作者（例如，法国高等师范学校）将进行专门的分析，如各种粘土矿物的量化和土壤生物的识别。 预期意义-新的信息将推进有关含铁矿物蚀变过程中电子损失/获得的生物和地球化学机制的知识。 根际土壤中新形成的膨胀粘土的一些益处包括增加必需营养素（例如，钾）和阳离子交换能力（或土壤储存养分的能力）。 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，通过从富铁材料获得电子将六价铬解毒为三价铬，将对铬污染土壤的修复具有实际应用。

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.