Determining the stable Fe isotope signature of plant-available iron in soils
Determining the stable Fe isotope signature of plant-available iron in soils
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DOI：
10.1016/j.chemgeo.2010.08.010
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发表时间：
2010-10-20
期刊：
影响因子：
3.9
通讯作者：
Stuetzel, Hartmut
中科院分区：
文献类型：
--
作者：
Guelke, Monika;von Blanckenburg, Friedhelm;Stuetzel, Hartmut
土壤中铁的同位素组成可以反映土壤形成的环境条件。但是植物只从土壤中提取移动的铁，这是土壤总铁的一小部分。然而，这一部分是出了名的难以实验提取。在这里，我们提供的证据表明，这种签名是很容易提供的战略II植物（草）的形式。采用两种不同的连续提取方法测定了两种农田土壤铁库的稳定Fe同位素特征。测定了以下土壤矿物质库的铁同位素组成：交换性铁、结晶性差的氧化物铁、有机质铁、结晶性氧化物铁和硅酸盐结合铁。我们发现不同土壤矿物库之间的铁同位素组成中δ Fe-56的变化约为1/mil（δ Fe-56/[千分之一] = [（Fe-56/54（样品）/Fe-56/54（IRMM-014））- 1]. 10（3））。对植物营养贡献最大的库是水可提取的和可交换的铁、有机质中的铁和结晶不良的（氧氢）氧化物中的铁。这些部分比散装土壤轻约0.3密耳。我们土壤中的硅酸盐具有高达千分之0.4的δ Fe-56，这表明在风化过程中优先损失轻Fe。我们比较了植物有效铁的同位素组成，典型的战略I和战略II的植物，生长在土壤中。虽然在根际氧化还原和其他转化过程中丰富的策略I植物在不同程度上轻铁同位素，策略II植物表现出均匀的铁同位素组成，只有轻微富集重铁同位素约0.3千分之一。因此，这些植物可能记录了土壤中植物有效铁的Fe同位素组成，可以与策略I植物的组成进行比较。(C)2010爱思唯尔有限公司版权所有。
The isotope composition of iron in soils can display the environmental conditions that formed this soil. But plants extract only the mobile iron from soil, which is a small fraction of the soils' total iron. Yet this fraction is notoriously difficult to extract experimentally. Here we provide evidence that this signature is provided readily in the form of strategy II plants (grasses). We determined the stable Fe isotope signature of iron pools in two agronomic soils with two different sequential extraction methods. The Fe isotopic composition of the following soil mineral pools was measured: exchangeable iron, iron of poorly-crystalline (oxyhydr)oxides, iron in organic matter, iron of crystalline oxides and silicate bound iron. We found variations of about 1 per mil in delta Fe-56 (delta Fe-56/[parts per thousand] = [(Fe-56/54(sample)/Fe-56/54(IRMM-014)) - 1].10(3)) in the iron isotopic composition between the different soil mineral pools. The pools that contribute most to plant nutrition are water-extractable- and exchangeable iron, iron in organic matter and iron of poorly-crystalline (oxyhydr)oxides. These fractions are about 0.3 per mil lighter than the bulk soils. Silicates in our soils have a delta Fe-56 of up to 0.4 parts per thousand, suggesting preferential loss of light Fe during weathering. We compared the isotope composition of the plant-available Fe to that of typical strategy I and strategy II plants, grown on the soils. While redox and other transformation processes in the rhizosphere enrich strategy I plants to varying degrees in light Fe isotopes, strategy II plants exhibit a uniform Fe isotopic composition and are only slightly enriched in the heavier iron isotopes by about 0.3 parts per thousand. Therefore these plants may record the Fe isotope composition of plant-available iron in soils, to which the composition of strategy I plants can be compared to. (C) 2010 Elsevier B.V. All rights reserved.