Due to the low iron solubility in alkaline soils, plants have evolved different iron acquisition strategies, which are either based on ferric iron reduction (strategy I) or complexation by phytosiderophores (strategy II). Recently, a prominent role of coumarins for iron acquisition has been discovered, but details of the respective mechanism remain unclear. Since coumarins may act as iron-binding ligands but also as reductants, various reaction sequences are possible, resulting in different iron species and oxidized coumarins. In this context, it is often overlooked that oxidized coumarins are not just byproducts of iron(III) reduction, but may be actively involved in further steps of iron mobilization. In order to verify this active role of oxidized coumarins in Fe(hydr)oxide dissolution, we complemented iron dissolution data with data of single coumarins (esculetin, scopoletin, fraxetin) and their oxidation products, as a function of time, pH, and mineral (goethite, lepidocrocite). Our results demonstrate that there are four different routes for coumarin oxidation, leading to quinones, dimers, hydroxylated coumarins, demethylated coumarins, and combinations of these. The time-dependent species pattern differs with respect to mineral, pH, and coumarin molecule. Oxidized coumarins are often more reactive than the original coumarins, explaining unexpected iron mobilization by scopoletin, which is demethylated to esculetin. Also oxidative hydroxylation and dimerization increase the number of phenolic groups and yield new chelating properties. Several iron-species are identified for the three coumarins. Since oxidation reactions are initiated directly at mineral surfaces, they are often very effective—but this does not always result in more iron mobilization.

由于碱性土壤中铁的溶解度低，植物已经进化出不同的铁获取策略，这些策略要么基于三价铁还原（策略 I），要么基于植物铁载体的络合（策略 II）。最近，发现了香豆素对铁获取的重要作用，但其各自机制的细节仍不清楚。由于香豆素可以作为铁结合配体，也可以作为还原剂，因此可能有各种反应序列，从而产生不同的铁种类和氧化的香豆素。在这种情况下，人们经常忽略氧化香豆素不仅是铁 (III) 还原的副产物，而且可能积极参与铁动员的进一步步骤。为了验证氧化香豆素在氧化铁（氢）氧化物溶解中的这种积极作用，我们用作为时间、pH 值和矿物质（针铁矿、纤铁矿）的函数的单一香豆素（七叶素、东莨菪碱、白曲松素）及其氧化产物的数据补充了铁溶解数据。我们的研究结果表明，香豆素有四种不同的氧化途径，分别产生醌、二聚体、羟基化香豆素、去甲基化香豆素以及它们的组合。时间依赖性物种模式在矿物质、pH 和香豆素分子方面有所不同。氧化的香豆素通常比原始的香豆素更具反应性，这解释了东莨菪碱意外的铁动员，东莨菪碱去甲基化为七叶素。氧化羟基化和二聚化也增加了酚基的数量并产生了新的螯合特性。为这三种香豆素确定了几种铁。