The availability of mineral nutrients for plants is determined by the chemical, physical and biological characteristics of soils, especially by root-induced changes in the rhizosphere. Mineral nutrient supply to the root surface is mediated mainly by mass flow or diffusion. Accordingly, root surface area is important for the acquisition of nutrients. Acquisition of most nutrients is particularly dependent upon root-induced changes in rhizosphere pH, redox potential and the release of low molecular weight organic solutes. Depending on their chemical nature, these solutes can mobilise mineral nutrients directly, in the case of organic acids and phytosiderophores, or indirectly, by enhancing the activity of microorgpnisms in the rhizosphere. Rhizosphere microorganisms may, however, also decrease nutrient availability or affect nutrient acquisiton via changes in root morphology caused by hormones or by the infection of plant roots with mycorehiza. Root-induced changes in the rhizosphere vary between genotypes, and are affected by the nutritional status of the plant (e.g. phosphorus or iron deficiency). The extent of root-induced changes in the rhizosphere is important for adaptation of higher plants to soils with extreme themical and physical properties.