Rhizosphere definition

In this chapter we review the current literature available on the influence of root exudates on rhizosphere microbial populations and the effects of plant, microbial and soil factors on the processes of rhizodeposition and microbial colonization and activity. We first give a brief overview and definitions of some of the main concepts relating to the rhizosphere and rhizodeposition. 

Since his early pioneering work on the rhizosphere (a term Hiltner used to describe specifically the interaction between bacteria and legume roots), our knowledge of the subject has greatly increased, and today perhaps a more appropriate definition of the rhizosphere is the field of action or influence of a root (1). The rhizosphere is generally considered to be a narrow zone of soil subject to the influence of living roots, where root exudates stimulate or inhibit microbial populations and their activities. The rhizoplane or root surface also provides a... 

Microorganisms at the rhizosphere are known to produce plant growth regulators using precursors released by the roots (71), which can influence root morphology (3) the degradation of these hormone-like substances could be prevented by their incorporation into humic molecules, which would preserve their chemical properties. However, definite proof is still lacking recent studies have shown the... 

Further progress may derive from a more accurate definition of the chemical and physical properties of the humic substances present at the rhizosphere and how they interact with the root-cell apoplast and the plasma membrane. An interaction with the plasma membrane H -ATPase has already been observed however this master enzyme may not be the sole molecular target of humic compounds. Both lipids and proteins (e.g., carriers) could be involved in the regulation of ion uptake. It therefore seems necessary to investigate the action of humic compounds with molecular approaches in order to understand the regulatory aspects of the process and therefore estimate the importance of these molecules as modulators of the root-soil interaction. 

By definition, all carbon (except above-ground littering) enters the soil via the rhizosphere, which is a highly dynamic and complex environment both in time and in space. As discussed in the Chaps. 2 and 4, the root excretions as well as root debris consist of a wide array of chemical compounds, most of which can be utilized by soil microorganisms (13). These compounds can be arbitrarily di-... 

Ectorhizosphere The soil layer surrounding roots and affected by the activity of roots themselves, and the microorganisms. The thickness of this soil portion usually ranges from one to a few millimetres. The ectorhizosphere was initially defined by Hiltner (1904), who referred to it simply as the rhizosphere. The same definition and term were reported by Curl and Truelove (1986). 

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