PDF(Pubmed)
Abstract：
The mobility and bioavailability of phosphate in paddy soils are closely coupled to redox-driven Fe-mineral dynamics. However, the role of phosphate during Fe-mineral dissolution and transformations in soils remains unclear. Here, we investigated the transformations of ferrihydrite and lepidocrocite and the effects of phosphate pre-adsorbed to ferrihydrite during a 16-week field incubation in a flooded sandy rice paddy soil in Thailand. For the deployment of the synthetic Fe-minerals in the soil, the minerals were contained in mesh bags either in pure form or after mixing with soil material. In the latter case, the Fe-minerals were labeled with 57Fe to allow the tracing of minerals in the soil matrix with 57Fe Mössbauer spectroscopy. Porewater geochemical conditions were monitored, and changes in the Fe-mineral composition were analyzed using 57Fe Mössbauer spectroscopy and/or X-ray diffraction analysis. Reductive dissolution of ferrihydrite and lepidocrocite played a minor role in the pure mineral mesh bags, while in the 57Fe-mineral-soil mixes more than half of the minerals was dissolved. The pure ferrihydrite was transformed largely to goethite (82-85%), while ferrihydrite mixed with soil only resulted in 32% of all remaining 57Fe present as goethite after 16 weeks. In contrast, lepidocrocite was only transformed to 12% goethite when not mixed with soil, but 31% of all remaining 57Fe was found in goethite when it was mixed with soil. Adsorbed phosphate strongly hindered ferrihydrite transformation to other minerals, regardless of whether it was mixed with soil. Our results clearly demonstrate the influence of the complex soil matrix on Fe-mineral transformations in soils under field conditions and how phosphate can impact Fe oxyhydroxide dynamics under Fe reducing soil conditions.
摘要：
水稻土中磷酸盐的迁移率和生物有效性与氧化还原驱动的铁矿物动力学密切相关。然而,磷酸盐在土壤中铁矿物溶解和转化过程中的作用尚不清楚。这里,我们研究了在泰国淹没的沙质稻田土壤中进行的16周田间孵化过程中，水铁矿和锂铁矿的转化以及磷酸盐预吸附到水铁矿上的影响。为了在土壤中部署合成铁矿物，矿物质以纯形式或与土壤材料混合后的形式装在网袋中。在后一种情况下，用57Fe标记Fe矿物，以允许用57FeMössbauer光谱追踪土壤基质中的矿物。监测了Porewater地球化学条件，使用57FeMössbauer光谱和/或X射线衍射分析分析了铁矿物组成的变化。在纯矿物网袋中，水铁矿和锂铁矿的还原溶解作用很小，而在57Fe-矿物-土壤混合物中，超过一半的矿物被溶解。纯水铁矿大部分转化为针铁矿（82-85％），16周后，水铁矿与土壤混合仅导致所有剩余57Fe的32％以针铁矿的形式存在。相比之下,当不与土壤混合时，锂铁矿仅转化为12％的针铁矿，但是当针铁矿与土壤混合时，在针铁矿中发现了所有剩余的57Fe的31％。吸附的磷酸盐强烈阻碍了水铁矿向其他矿物的转化，不管它是否与土壤混合。我们的结果清楚地证明了在田间条件下复杂的土壤基质对土壤中铁矿物转化的影响，以及磷酸盐如何在减少铁的土壤条件下影响羟基氧化铁的动力学。
