Rhizosphere

(geology) The soil region subject to the influence of plant roots and characterized by a zone of increased microbiological activity.

The soil region subject to the influence of plant roots. It is characterized by a zone of increased microbiological activity and is an example of the relationship of soil microbes to higher plants.

A sharp boundary cannot be drawn between the rhizosphere and the soil unaffected by the plant (edaphosphere). At the root surface the rhizosphere effect is most intense, falling off sharply with increasing distance.

Growth of a plant markedly changes the microbial population of soil within its influence. In the rhizosphere there are more microorganisms than in soil distant from the plant. This increase is most pronounced with bacteria but is evident with other groups. The rhizosphere effect is seen in seedling plants; it increases with the age of the plant and usually reaches a maximum at the stage of greatest vegetative growth. Upon death of the plant the microbial population reverts to the level of the surrounding soil. Leguminous plants support higher rhizosphere populations than nonlegumes. The stimulation of microorganism growth in the rhizosphere results chiefly from the liberation of readily available organic substances by the growing plant. See also Soil microbiology.