The rhizosphere: Molecular interactions between microorganisms and roots.

The rhizosphere has a large impact on plant performance in several ways. A stand-specific, more or less high diversity of microorganisms not only supports the plant in the acquisition of water and nutrients, but also modulates its ability to cope with pathogens. This diversity, however, has to be maintained and thus causes a considerable drain of photoassimilates, which are then not available for shoot development. In this chapter, we try to explain why the considerable allocation of carbon to the root system is a “wise” decision by the plant. We thus focus on the function of root-associated bacteria and their relevance for plant growth and development of disease resistance, and deliver data on the molecular basis of the root–fungus symbiosis (mycorrhiza)