Geochemical patterns and microbial contribution to iron plaque formation in the rice plant (Oryza sativa) rhizosphere

水稻是世界上一半以上人口的主要食物来源，而全世界80%的水稻种植都是在涝渍水稻土上进行的。在土壤中和土壤-水界面建立还原条件不仅刺激微生物产生和释放温室气体甲烷。这些设置还为微生物铁（III）还原创造了最佳条件，因此使系统充满还原的亚铁。通过还原和溶解以其高表面活性为特征的铁矿物，吸附的营养物质和污染物（例如东南亚的砷）将被动员起来，从而可供植物吸收。水稻植物已经进化出一种从根部释放氧气的策略，以防止在高含铁环境中铁的分解。还原性水稻土释放的氧气导致水稻根上形成铁膜，最终增加了对有毒金属的吸附能力。到目前为止，控制铁斑形成的地球化学和微生物过程还没有被破译。据推测，铁（II）氧化细菌发挥了潜在的作用，铁（III）矿物形成沿着根。然而，它们在根际的空间分布，其丰富的模式作为植物生长的功能和它们的潜力，以控制当地的铁氧化还原循环从未被详细研究。建议的研究的目标是评估的贡献，铁（II）氧化，从而铁（III）矿物沉淀细菌铁菌斑形成水稻根。为此，我们首先打算映射和相关的高分辨率（生物）地球化学和铁矿物学模式在水稻根际水稻生长的功能。在第二步中，铁（II）-氧化和铁（III）-还原群体将在整个建立的氧化还原梯度在植物的定义的营养阶段进行量化。第三，将在生长实验中对从韦尔切利（意大利）采样的天然水稻土中分离的细菌的铁（II）氧化和铁（III）还原速率进行定量。最后，将通过一系列实验来评估微生物对铁斑形成的贡献，其中水稻植物在无菌地球化学控制的设置中种植，该设置中添加了分离的微需氧铁（II）氧化细菌。 结合数据集将提供的空间和时间变化的贡献，以及在水稻根际微生物铁矿物的生产和溶解的变化的见解。所获得的知识将提供一个很好的基础研究污染物（IM）移动通过铁膜的形成和潜在的应用水稻种植作为粮食交付和土壤修复行动并行。

Rice is the major food source for more than half of the world population and 80 percent of the worldwide rice cultivation is performed on water logged paddy soils. The establishment of reducing conditions in the soil and across the soil-water interface not only stimulates the microbial production and release of the greenhouse gas methane. These settings also create optimal conditions for microbial iron(III) reduction and therefore saturate the system with reduced ferrous iron. Through the reduction and dissolution of ferric minerals that are characterized by their high surface activity, sorbed nutrients and contaminants (e.g. arsenic in South East Asia) will be mobilized and are thus available for uptake by plants. Rice plants have evolved a strategy to release oxygen from their roots in order to prevent iron toxification in highly ferrous environments. The release of oxygen to the reduced paddy soil causes ferric iron plaque formation on the rice roots and finally increases the sorption capacity for toxic metals. To this date the geochemical and microbiological processes that control the formation of iron plaque are not deciphered. It has been hypothesized that iron(II)-oxidizing bacteria play a potential role in the iron(III) mineral formation along the roots. However, their spatial distribution within the rhizosphere, their abundance pattern as a function of plant growth and their potential to control the local iron redox cycling has never been investigated in detail. The goal of the proposed study is to evaluate the contribution of Fe(II)-oxidizing and thus Fe(III) mineral precipitating bacteria to iron plaque formation on rice roots. To this end, we first intend to map and correlate high resolution (bio)geochemical and iron-mineralogical patterns in the rice plant rhizosphere as a function of rice growth. In a second step, iron(II)-oxidizing and iron(III)-reducing populations will be quantified throughout the established redox gradients at defined vegetative stages of the plant. Thirdly, iron(II) oxidation and iron(III) reduction rates of isolated bacteria from native paddy soil sampled in Vercelli (Italy), will be quantified in growth experiments. And finally, the microbial contribution to iron plaque formation will be evaluated by an experimental series in which the rice plants are cultivated in a sterile geochemically controlled set-up that has been spiked with isolated microaerophilic iron(II)-oxidizing bacteria. The combined dataset will provide insights on the spatially and temporally varying contribution, as well as on the variation of microbial ferric mineral production and dissolution in the rice plant rhizosphere. The acquired knowledge will provide an excellent basis research on contaminant (im)mobilization through iron plaque formation and the potential to apply rice cultivation as food delivering and soil remediation action in parallel.