Rhizosphere chemistry influencing plant nutrition

This chapter describes the physicochemical processes determining the rhizosphere as a soil compartment influenced by the activity of roots and the consequences for plant nutrition. An introductory section discusses properties and the spatial extent of the rhizosphere as well as the temporal variability of rhizosphere processes. The mechanisms determining root-induced modifications of the pH and the redox conditions in the rhizosphere are discussed with respect to effects on the solubility and plant availability of nutrients and toxic elements and the impact on plant–microbe interactions. A final section describes the composition, quantity, and the release mechanisms of organic compounds by plant roots (rhizodeposition) and their role in rhizosphere processes, covering turnover of fine root structures and mycorrhizal hyphae, diffusion-mediated losses of organic substances from root cells but also the controlled release of root border cells, mucilage, ectoenzymes, and various low-molecular-weight compounds with specific adaptive functions regarding nutrient acquisition and stress tolerance.