الفهرس 
1. INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Soil is an excellent niche of growth of many microorganisms: protozoa, fungi, viruses, and bacteria. Some microorganisms are able to colonize soil surrounding plant roots, the rhizosphere, making them come under the influence of plant roots (Hiltner 1904; Kennedy 2005).
Soil-plant ecosystem depends on microbial activities which in turn contribute towards improving soil health, environmental quality and crop production. Soil microorganisms are important because they affect the soil’s physical, chemical, and biological properties.
The rhizosphere is the volume of soil surrounding and under the influence of plant roots, and the rhizoplane is the plant root surfaces and strongly adhering soil particles (Kennedy, 2005). In the rhizosphere, very important and intensive interactions are taking place between the plant, soil and microorganisms.
In 1904 the German agronomist and plant physiologist Lorenz Hiltner first coined the term ”rhizosphere” to describe the plant-root interface, a word originating in part from the Greek word ”rhiza”, meaning root (Hiltner, 1904; Hartmann et al., 2008). Hiltner described the rhizosphere as the area around a plant root that is inhabited by a unique population of microorganisms influenced, he postulated, by the chemicals released from plant roots. In the years since, the rhizosphere definition has been refined to include three zones which are defined based on their relative proximity to, and thus influence from, the root (Figure 1). The endorhizosphere includes portions of the cortex and endodermis in which microbes and cations can occupy the ”free space” between cells (apoplastic space). The rhizoplane is the medial zone directly adjacent to the root including the root epidermis and mucilage. The outermost zone is the ectorhizosphere which extends from the rhizoplane out into the bulk soil. The rhizosphere is not a region of definable size or shape, but instead, consists of a gradient in chemical, biological and physical properties which change both radially and longitudinally along the root.