Plants joining forces: Utilizing synergies between plant iron acquisition strategies for improving iron uptake and crop yields

To feed the world population in a sustainable manner there is an immanent need for agriculture to make more efficient use of nutrients already present in the soil. Iron (Fe) is an essential micronutrient for plants that is abundantly present in soils, but, due to its poor bioavailability, limits crop yields on one-third of the earth’s land surface, including vast areas in China such as the löss plateau. Plants species have different strategies for coping with conditions of low Fe availability: Strategy I plants exude reductants to reduce soil Fe(III) to the more soluble and bioavailable Fe(II), and Strategy II plants exude phytosiderophores, i.e. chelating ligands that form soluble, bioavailable Fe(III)-complexes. Rapid re-oxidation of Fe(II) and competitive complexation of other metals limit the effectiveness of these strategies. However, recently, it was found in batch experiments that mixtures of phytosiderophores and reductants can synergistically mobilize Fe from soil. This suggests that Strategy I and II plants may be more effective at increasing Fe bioavailability when grown in close association, providing a novel conceptual angle to the potential benefits of intercropping. The objective of this project is: 1) to obtain a mechanistic and quantitative understanding of synergistic Fe mobilization from soils by plant ligands and reductants, and 2) to explore if synergistic Fe mobilization can be utilized for enhancing Fe uptake by crop plants. The mechanisms and constraints of synergistic Fe mobilization by phytosiderophores and plant reductants will be examined in batch experiments in soil and mineral suspensions systems. The processes by which soil organic matter and manganese oxides influence synergistic Fe mobilization will be elucidated. Furthermore, it will be investigated how soil properties and environmental conditions constrain synergistic Fe mobilization. The potential for enhanced Fe uptake will be explored by characterizing the composition of exudates from Strategy I and Strategy II plants grown in hydroponic systems under Fe deficiency and by examining the capacity of the exudates to mobilize Fe from soil, both separately and in mixtures. Promising combinations of Strategy I and Strategy II plant species will subsequently be grown on soil, and Fe availability, Fe uptake and biomass yield will be compared for species grown separately and in combination. This project will 1) contribute to a better understanding of the interactive effects between plant Fe acquisition strategies, 2) offer new insights into the composition of root exudates for an array of crop species grown under Fe deficiency, and 3) provide information for the (Chinese) agricultural sector on the benefits of growing specific combinations of crops for enhanced nutrient acquisition and crop yield.