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Abstract
Synergistic effects between ligand- and reductant-based Fe acquisition strategies can enhance the mobilization of Fe, but also of competing metals from soil. For phytosiderophores, this may alter the time and concentration window of Fe uptake during which plants can benefit from elevated Fe concentrations. We examined how the size of this window is affected by the ligand and reductant concentration and by non-simultaneous addition. To this end, a series of kinetic batch experiments was conducted with a calcareous clay soil to which the phytosiderophore 2′-deoxymugineic acid (DMA) and the reductant ascorbate were added at various concentrations, either simultaneously or with a one- or two-day lag time. Both simultaneous and non-simultaneous addition of the reductant and the phytosiderophore induced synergistic Fe mobilization. Furthermore, initial Fe mobilization rates increased with increasing reductant and phytosiderophore concentrations. However, the duration of the synergistic effect and the window of Fe uptake decreased with increasing reductant concentration due to enhanced competitive mobilization of other metals. Rate laws accurately describing synergistic mobilization of Fe and other metals from soil were parameterized. Synergistic Fe mobilization may be vital for the survival of plants and microorganisms in soils of low Fe availability. However, in order to optimally benefit from these synergistic effects, exudation of ligands and reductants in the rhizosphere need to be carefully matched.
Highlights
Iron (Fe) is an essential micronutrient to plants and most microorganisms [1,2]
Lag time between addition of reductant and chelating ligand—To investigate if metal mobilization by phytosiderophores that are released in a diurnal pulse may be affected by reductants that have been released before the phytosiderophores exudation pulse, we investigated the effect of a lag time between PS and reductant additions on metal mobilization as a function of time. 1 mM ascorbate was added, either simultaneously, or one or two days prior to a 100 μM deoxymugineic acid (DMA) addition
Our results demonstrate that it is not required that ligands and reductants are exuded simultaneously for generating synergistic Fe mobilization
Summary
Iron (Fe) is an essential micronutrient to plants and most microorganisms [1,2] It is abundant in most environments, it is not always sufficiently bioavailable, in environments with a circumneutral pH, e.g., calcareous soils [3]. Plants have developed Fe acquisition strategies to cope with low Fe availability [6,7]. These strategies are largely based on classical mineral dissolution mechanisms: proton-promoted dissolution, reductive dissolution and ligand-promoted dissolution [8,9]. -called Strategy I plants increase proton exudation, exude reductants and upregulate the ferric chelate reductase activity to lower the pH and reduce Fe(III) to the more soluble Fe(II) [2]. Phytosiderophores can form soluble complexes with soil-Fe that can readily be taken up by the plant roots [13]
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