Two humic acids extracted from a volcanic soil (HA1) and a leonardite (HA2) were used to form insoluble complexes with iron metals. To simulate the rhizospheric processes that displace iron from complexes of humic molecules and solubilize the soil humeome, the insoluble iron–humates were treated with a solution of siderophore deferoxamine mesylate (DFOM) and a mixture of citric, oxalic, tartaric and ketoglutaric acids, at different concentrations and contact times. Results showed that the removal of iron from humic complexes varied depending on the concentration of the extractants and extraction times. At large concentration, the mixture of organic acids was generally a better extractant than the siderophore, probably because of their lower solution pH. However, at smaller concentrations, the extracting capacity of the DFOM solution and the mixture of organic acids was generally similar. Differences in iron extractability between the two iron–humates were attributed to both the humic molecular composition and the steric hindrance of the extractants. Iron was more easily released from complexes formed with HA1 rich in aliphatic C than from those of HA2 rich in aromatic C, possibly because the more flexible conformational structure of HA1 was more accessible to the bulky DFOM than the rigid conformation of iron complexes made by the largely aromatic HA2. This work provided evidence that iron–humate complexes may be potentially used to enhance iron nutrition of plants, whose exudates rich in organic acids, together with the siderophores produced by rhizospheric microbes, can displace iron from complexes and enhance its solubility. Concomitantly, the same process may solubilize humic molecules from the same iron–humates, thereby enhancing the concentration of bioactive humic matter in the soil solution.

中文翻译：

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植物根系分泌物和微生物铁载体可能改变铁-腐植酸复合物

从火山土壤（HA1）和渗碳体（HA2）提取的两种腐殖酸被用来与铁金属形成不溶性络合物。为了模拟从腐殖质分子复合物中置换铁并溶解土壤腐殖质的根际过程，在不溶性铁-腐植酸溶液中加入铁氧体去铁胺甲磺酸盐（DFOM）以及柠檬酸，草酸，酒石酸和酮戊二酸的混合物进行处理。不同的浓度和接触时间。结果表明，从腐殖质络合物中去除铁取决于萃取剂的浓度和萃取时间。在高浓度下，有机酸的混合物通常比铁载体更好的萃取剂，可能是因为它们的溶液pH值较低。但是，在较小的浓度下 DFOM溶液和有机酸混合物的萃取能力通常相似。两种铁-腐殖酸盐之间铁的可萃取性差异归因于萃取剂的腐殖质分子组成和位阻。铁比富含脂肪族C的HA1形成的络合物更容易释放，而不是富含芳香族C的HA2形成的络合物释放铁，这可能是因为笨重的DFOM更容易获得HA1的柔性构象结构，而不是由铁形成的铁络合物的刚性构象。主要为芳香族HA2。这项工作提供了证据表明，腐殖酸铁络合物可潜在地用于增强植物的铁营养，富含有机酸的渗出液与根际微生物产生的铁载体可以取代络合物中的铁并提高其溶解度。