The Rhizosphere

The Rhizosphere:

The microbial ecology of the rhizosphere (the region of soil immediately surrounding the roots of plants) is significantly different from the rest of the soil. The microorganisms in these regions are not as intimately associated with plants as mycorrhizae are, but they do have a profound effect on plant growth. Specific kinds of microorganisms concentrate in the rhizosphere. This concentration, termed the rhizosphere effect, is described quantitatively be the ratio of the concentration of microorganisms in the rhizosphere to concentration in adjacent soil known as the R:S ratio. For Gram-positive bacteria, actinomycetes, protozoa, and algae, the R:S ratio is relatively small, only about 2 or 3. But for gram-negative bacteria particularly species of Pseudomonas, Flavobacterium, and Alcaligenes, the R:S ratio can be several hundred. Specific microorganisms concentrate in the rhizosphere because plant roots excrete both nutrients and antimicrobial agents, The antimicrobial agent are selective, they inhibit some microorganisms but not others, Thus, microorganisms in the rhizosphere. For example, barley (which is high in calcium) associated with a normal rhizosphere micro biota takes up phosphate about twice as effectively as barley grown in sterile soil. Moreover, the rhizosphere micro biota protects against fungal pathogens that attack plant roots.

In summary, soil is a beehive of microbial activity. The hue number and variety of microorganisms there carry out numerous activates that benefit Earthâ??s ecology. They mineralize organic waste, thy fix nitrogen, and they stimulate plant growth. While most are beneficial some cause plant diseases, and others are human pathogens. Regardless of their roles they are all of the is earth and all play a part in the circle of life.