Abstract
Background and aimsGraminaceous plants are grown worldwide as staple crops under a variety of climatic and soil conditions. They release phytosiderophores for Fe acquisition (Strategy II). Aim of the present study was to uncover how the rhizosphere pH, background electrolyte and temperature affect the mobilization of Fe and other metals from soil by phytosiderophores.MethodsFor this purpose a series of kinetic batch interaction experiments with the phytosiderophore 2′-deoxymugineic acid (DMA), a calcareous clay soil and a mildly acidic sandy soil were performed. The temperature, electrolyte concentration and applied electrolyte cation were varied. The effect of pH was examined by applying two levels of lime and Cu to the acidic soil.ResultsFe mobilization by DMA increased by lime application, and was negatively affected by Cu amendment. Mobilization of Fe and other metals decreased with increasing ionic strength, and was lower for divalent than for monovalent electrolyte cations at equal ionic strength, due to higher adsorption of metal-DMA complexes to the soil. Metal mobilization rates increased with increasing temperature leading to a faster onset of competition; Fe was mobilized faster, but also became depleted faster at higher temperature. Temperature also affected biodegradation rates of metal-DMA complexes.ConclusionRhizosphere pH, electrolyte type and concentration and temperature can have a pronounced effect on Strategy II Fe acquisition by affecting the time and concentration ‘window of Fe uptake’ in which plants can benefit from phytosiderophore-mediated Fe uptake.
Highlights
Iron (Fe) acquisition by plants grown on alkaline soils is limited by the low solubility and slow dissolution kinetics of iron-bearing minerals (Takagi 1976; Kraemer et al 2006)
In order to examine the influence of pH and liming on competitive complexation of Cu and Fe mobilization by deoxymugineic acid (DMA), the Cu content of the soil was raised by Cu application
The results from the soil interaction experiments provide insights in how metal mobilization by phytosiderophores is affected by rhizosphere pH, electrolytes and temperature
Summary
Iron (Fe) acquisition by plants grown on alkaline soils is limited by the low solubility and slow dissolution kinetics of iron-bearing minerals (Takagi 1976; Kraemer et al 2006). Strategy II plants (graminaceous plants) exude phytosiderophores (PS), which are chelating ligands with a high affinity for Fe. PS comprise a relatively small group of ligands including mugineic acid (MA) and its derivatives 3′-epihydroxymugineic acid (epi-HMA) and 2′deoxymugineic acid (DMA) (Murakami et al 1989). PS comprise a relatively small group of ligands including mugineic acid (MA) and its derivatives 3′-epihydroxymugineic acid (epi-HMA) and 2′deoxymugineic acid (DMA) (Murakami et al 1989) They form hexadentate complexes with Fe through binding with aminocarboxylate and hydroxycarboxylate functional groups (Kraemer 2004). Graminaceous plants are grown worldwide as staple crops under a variety of climatic and soil conditions. They release phytosiderophores for Fe acquisition (Strategy II). Aim of the present study was to uncover how the rhizosphere pH, background electrolyte and temperature affect the mobilization of Fe and other metals from soil by phytosiderophores
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