Rhizosphere

The rhizosphere is the area of soil that is directly impacted by root secretions and related soil microorganisms. 

Plants interact with the surrounding environment through chemical reactions, ion exchanges and complex trade agreements with soil microorganisms. The majority of these interactions occur below ground, in the rhizosphere.

Rhizosphere illustration: A=amoeba consuming bacteria; BL/BU=bacteria; RC=Root derived carbon; SR=Sloughed root hair cells; F=Fungal hyphae; N=nematode (Smartse) CC BY-SA 3.0

Root secretions contain acids, sugars and amino acids. These secretions help plants obtain nutrients and protect against pathogens. They also stabilize soil aggregates.

The rhizosphere is broken down into three regions:

• endorhizosphere - areas of direct contact (inside and outside) the root endodermis
• rhizoplane - areas directly adjacent to the roots
• ectorhizoplane - the area that extends to unaffected bulk soil

From the inside out

Working from the inside and just around the roots of most plants, microscopic fungi (mycorrhizae) exchange water, hormones and mineral elements found within the soil for sugar created by the plant through photosynthesis.

Rhizobium bacteria have a symbiotic relationship with members of the legume family. They detect flavonoids secreted by plant roots, which stimulates the bacteria to generate nod factors. These nod factors trigger the plant to form root nodules. The rhizobium bacteria then provide the plant with nitrogen from the atmosphere. There are other nitrogen fixing non-symbiotic bacteria within the rhizosphere that aid other plants in exchange for sugars and other nutrients.

Some plants also produce allelochemicals within and beyond the rhizosphere that prohibit other plants from growing nearby.

Just as we constantly lose skin cells, plants also shed cells. These cells fall to the ground (rhizodeposition) and are eaten by bacteria. The bacteria, in turn, are eaten by nematodes and protozoa. This process enriches the soil, making nutrients available to plants and improving soil health.