Mobilisation of Nickel by hyperaccumulating plants

In areas, where nickel-containing serpentine minerals occur close to the surface, Nickel-rich soils have developed. Due to the high nickel concentration in these soils a specific plant species community adapted to the local conditions can be typically found. A certain group of plant species has developed a very specific strategy, i.e. accumulating nickel in the leav es. These plants are called hyperaccumulators. Whereas some processes involved in uptake and storage of nickel are already to some extent clarified, processes of nickel mobilization in root-near soil are still largely unknown. Since only a small fraction of nickel in soil is soluble (and thus bioavailable), it is likely that root-released compounds contribute to the solubilization of nickel. The characteristics of these compounds, so-called root exudates, and their role in nickel mobilization are not known yet. Thus, the aim of this project is to collect and characterize the root exudates of nickel hyperacumulators grown in specific growth containers, so-called rhizoboxes. For clarifying their effect on nickel mobilsation in soil, a novel technology of isotope fractionation will be applied. Isotopes are elemental varieties with the same chemical characteristics, but different masses. Since the reaction speed in chemical or physical processes can differ between isotopes, small but detectable changes in the isotopic composition may occur. By analyzing the isotopic composition of nickel and iron it will be tried to identify the source, i.e. the soil chemical fraction of nickel, mobilized by the plants. A further aspect investigated in this project is the contribution of soil microorganisms to nickel mobilization and plant uptake. Whereas the contribution of soil bacteria on plant growth and nickel uptake is already known, the role of fungi in soil, on the root surface or in root tissues is still unknown and will therefore be investigated in this project. The project is an interdisciplinary collaboration between two Austrian Universities (Universität für Bodenkultur Wien, Montanuniversität Leoben), the CNRS in Pau (Frankreich) and the Jagiellonian University in Krakw (Poland), funded by the FWF (P34719).