Abstract
Iron is an essential micronutrient for most organisms due to its role in fundamental metabolic processes. In cultivated soils, soil solution iron is mostly oxidized [Fe(III) species] unless local anoxic conditions develop. The concentration of these Fe(III) species is small in soil solution due to the low solubility of ferric oxides, oxyhydroxides, and hydroxides, which is minimal at neutral and alkaline pH. In the rhizosphere, iron concentration in the soil solution is even lower because of its uptake by aerobic organisms (plants and microorganisms), leading to a high level of competition for Fe(III). In order to face iron competition, these organisms have evolved active uptake strategies based on acidification, chelation, and/or reduction processes. Iron competition plays a major role in microbial and plant-microbe interactions in the rhizosphere. This review summarizes current knowledge on the iron status in soils and rhizospheres, and the acquisition strategies of plants and microbes. This review also shows how the dynamic interactions between soil minerals, plants, and microorganisms impact plant health and nutrition. Analysis of these complex interactions offers an interesting case study of research on rhizosphere ecology integrating different scientific expertises and approaches.