Abstract Acquisition of Fe(III) from hardly soluble Fe oxyhydroxides by bacteria, fungi and plants in soil is often facilitated by Fe(III)-chelating siderophores. While the siderophore-promoted dissolution of pure Fe oxyhydroxides and the influence of defined low molecular weight organic acids has been investigated meticulously, studies examining Fe oxyhydroxides coated with more complex adsorbed organic matter (OM) or Fe-OM coprecipitates have been sparse. This study therefore explored the impact of the composition of both adsorbed and coprecipitated OM on the siderophore-promoted dissolution of ferrihydrite (Fh) in relation to (i) surface site coverage and pore blockage, (ii) aggregation state, (iii) charge characteristics and (iv) crystallinity. In addition to pure Fh, Fh-OM adsorption complexes and Fe-OM coprecipitates were synthesized using OM of different origins (extracellular polymeric substances of Bacillus subtilis, natural OM (NOM) extracted from soil Oi and Oa horizons). The Fe-organic associations were characterized by N2 gas adsorption, X-ray photoelectron spectroscopy (XPS), electrophoretic mobility, particle size measurements and desorption experiments. Siderophore-mediated dissolution experiments with desferrioxamine-B (DFOB) were conducted at pH 4 and 7. At pH 4, adsorbed OM provided a more effective protection against DFOB due to its larger sorption affinity. At pH 7, the surface site blockage by adsorbed OM at comparable C loadings was less effective, while less aggregated particles were more prone to dissolution. For OM coprecipitated with Fe, there was no distinct accelerating or inhibiting effect on DFOB-promoted dissolution to be found. Initial Fe dissolution rates at given soil conditions were thus affected by both the type of OM and the sorption procedure. Our results therefore corroborate the importance of considering the heterogeneous composition of soil OM when investigating the mobilization of Fe-organic associations.

中文翻译：

---

铁载体促进与吸附和共沉淀天然有机物相关的水铁矿溶解

摘要 Fe(III) 螯合铁载体通常会促进土壤中细菌、真菌和植物从难溶性 Fe 羟基氧化物中获取 Fe(III)。虽然铁载体促进纯 Fe 羟基氧化物的溶解和定义的低分子量有机酸的影响已被仔细研究，但对覆盖有更复杂吸附有机物 (OM) 或 Fe-OM 共沉淀物的 Fe 羟基氧化物的研究很少。因此，本研究探讨了吸附和共沉淀 OM 的组成对铁载体促进的水铁矿 (Fh) 溶解的影响，与 (i) 表面位点覆盖和孔隙堵塞、(ii) 聚集状态、(iii) 电荷特性有关(iv) 结晶度。除了纯 Fh，Fh-OM 吸附复合物和 Fe-OM 共沉淀物是使用不同来源的 OM 合成的（枯草芽孢杆菌的胞外聚合物，从土壤 Oi 和 Oa 层中提取的天然 OM (NOM)）。Fe-有机结合物的特征在于 N2 气体吸附、X 射线光电子能谱 (XPS)、电泳迁移率、粒度测量和解吸实验。铁载体介导的去铁胺-B (DFOB) 溶解实验在 pH 4 和 7 下进行。在 pH 4 时，吸附的 OM 由于其更大的吸附亲和力提供了更有效的抗 DFOB 保护。在 pH 7 时，在可比 C 负载下吸附的 OM 对表面位点的阻塞效果较差，而较少聚集的颗粒更容易溶解。对于与 Fe 共沉淀的 OM，没有发现对 DFOB 促进的溶解有明显的加速或抑制作用。因此，给定土壤条件下的初始 Fe 溶解速率受 OM 类型和吸附程序的影响。因此，我们的结果证实了在研究 Fe-有机结合的动员时考虑土壤 OM 的异质成分的重要性。