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18th International Symposium on Iron Nutrition and Interaction in Plants Madrid – May 30-June 3 2016 THE GEOCHEMISTRY OF STRATEGY II PLANT IRON UPTAKE Stephan M. Kraemer*, Walter Schenkeveld Department of Environmental Geochemistry and Environmental Research Network, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria. *[email protected] ABSTRACT: While some underlying basic problems and fundamental biogeochemical and physiological solutions to plant iron acquisition from soils have been explored by pioneering research over several decades, a full mechanistic, quantitative and predictive understanding of the pertinent plant soil interactions is still lacking. Any physiological activity at the root surface addresses a complex and highly non-linear biogeochemical reaction network. Interactions and feedback loops between root activity and soil reactivity are inherently difficult to understand – the co-location of the soil/root interface with scientific disciplinary boundaries constitutes just one impediment - but the intellectual challenges associated with this issue also provide an exciting field for scientific research. This presentation gives an overview over soil biogeochemical aspects of plant iron acquisition with a particular focus on Strategy II iron acquisition mechanisms. It is shown that specificity of the acquisition mechanism for the target nutrient iron is of high importance for the efficiency of the process. However, specificity is usually understood in terms of thermodynamic properties of the ligand and its iron complex versus other metal complexes. Here, the concepts of thermodynamic versus kinetic specificity are explored, based on the coordination chemical properties of biogenic ligands and their interaction with the soil chemical reaction networks. This discussion leads to an understanding of the time dependence of iron mobilization processes that we conceptualize as a concentration/time window of iron acquisition. An overview of processes and feedbacks constraining this window of iron acquisition is given. Also, scaling problems are discussed that may lead to wrong conclusions if the non-linear effects of experimental parameters are not properly considered. Keywords: Rhizosphere, geochemistry, window or iron uptake, phytosiderophores, kinetics ACKNOWLEDGEMENT Funding for this work is provided by the Austrian FWF grant Preferred Presentation format: (ORAL (invited)). Selected Sessions: (please, indicate the name of the session from these): • Iron chemistry and dynamics in soils . 1 I 1528-N19.