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The Rhizosphere

November 12, 2016

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THE RHIZOSPHERE

The rhizosphere is the word used to describe the area of soil surrounding plant roots. It is the most biologically active layer of the soil; populated with micro organisms interacting and benefiting from chemicals released by plant roots (1,2,7). There are more micro organisms present in a teaspoon of soil than there are people on the earth; the rhizosphere can carry 1000-2000 times this amount making it highly populated with microbial life (2). The rhizosphere has three zones (2,9,10)-the endorhizosphere, the rhizoplane and the ectorhizosphere (figure 1).

1. The endorhizosphere: This is the inner section of the rhizosphere. It is the section of the plant root occupied by micro organisms (which benefit from organic compounds released by roots).

2. The rhizoplane: This is the middle section of the rhizosphere. It includes the plant root surface with soil particles adhering to it.

3. The ectorhizosphere: The outer area of soil surrounding the roots.

Figure 1: Image of the rhizosphere showing its three described sections-the endorhizosphere, the rhizoplane and the ectorhizosphere. Source: McNear H. (2013)
Figure 1: Image of the rhizosphere showing its three described sections-the endorhizosphere, the rhizoplane and the ectorhizosphere. Source: McNear H. (2013)

RHIZODEPOSITION

Rhizodeposition is what makes the rhizosphere an interesting place for biological study. Plant roots release organic compounds into their surrounding soils (1). These compounds are what scientists refer to as rhizodeposits and the process is called rhizodeposition. As plants release organic compounds from their roots they lose some of their carbon to the surrounding soil; this means that they contribute to the soil carbon content (3). So the soil benefits from the plants lost carbon. The release of organic compounds in the root zone also supports the soil microbial life (3). The amount and composition of rhizodeposits from plant roots vary depending on the type of plant, the climate, the nutrient deficiency, and the physical, chemical and biological properties of soil surrounding the root (2). Rhizodeposits are released through the following ways (3):

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