Abstract
AimsTo test if multi–surface models can provide a soil-specific prediction of metal mobilization by phytosiderophores (PS) based on the characteristics of individual soils.MethodsMechanistic multi-surface chemical equilibrium modeling was applied for obtaining soil-specific predictions of metal and PS speciation upon interaction of the PS 2’-deoxymugineic acid (DMA) with 6 soils differing in availability of Fe and other metals. Results from multi-surface modeling were compared with empirical data from soil interaction experiments.ResultsFor soils in which equilibrium was reached during the interaction experiment, multi-surface models could well predict PS equilibrium speciation. However, in uncontaminated calcareous soils, equilibrium was not reached within a week, and experimental and modeled DMA speciation differed considerably. In soils with circum-neutral pH, on which Fe deficiency is likely to occur, no substantial Fe mobilization by DMA was predicted. However, in all but the contaminated soils, Fe mobilization by DMA was observed experimentally. Cu and Ni were the quantitatively most important metals competing with Fe for complexation and mobilization by DMA.ConclusionThermodynamics are unable to explain the role of PS as Fe carrier in calcareous soils, and the kinetic aspects of metal mobilization by PS need to be closer examined in order to understand the mechanisms underlying strategy II Fe acquisition.Electronic supplementary materialThe online version of this article (doi:10.1007/s11104-014-2128-3) contains supplementary material, which is available to authorized users.
Highlights
Strategy II Fe acquisition, which is employed by graminaceous plants, is characterized by root exudation of a class of chelating agents called phytosiderophores (PS) (Takagi et al 1984; Takagi 1976), for the purpose of facilitating the transport of soil-Fe towards the root surface (Marschner et al 1986)
For soils in which equilibrium was reached during the interaction experiment, multi-surface models could well predict PS equilibrium speciation
In uncontaminated calcareous soils, equilibrium was not reached within a week, and experimental and modeled deoxymugineic acid (DMA) speciation differed considerably
Summary
Strategy II Fe acquisition, which is employed by graminaceous plants, is characterized by root exudation of a class of chelating agents called phytosiderophores (PS) (Takagi et al 1984; Takagi 1976), for the purpose of facilitating the transport of soil-Fe towards the root surface (Marschner et al 1986). PS diffuse away from the root towards a soil particle, where the PS chelate and mobilize Fe (Kraemer et al 2006; Lindsay and Schwab 1982). At the root surface the FePS complex is taken up by a high affinity transporter (Römheld and Marschner 1986). It was discovered that PS do not exclusively bind and mobilize Fe, and several other trace nutrients, Zn, Cu and Mn (Treeby et al 1989; Zhang et al 1991), as well as Ni and Cd (Awad and Römheld 2000). As a result of microbial degradation of the metal-PS complexes, metal mobilization proved to be only temporary (Takagi et al 1988)
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