Introduction to Soil Chemistry

50 soil basics iii
Figure 3.3. Plant roots with adhering soil illustrating the interaction between plant roots and soil.
Any one of these criteria can be used to distinguish an area around the
roots, called the rhizosphere, from bulk soil. In addition to these general characteristics,
the rhizosphere is the area, as shown in Figure 3.4 around plant
roots where there is high microbial activity, increased carbon dioxide,
decreased oxygen, decreased water and nutrient content, and decreased pH.
These conditions develop because of root metabolic activity, exudates, and
cells sloughed off by roots. Root exudates are specific for each plant and
contain a wide range of organic and inorganic compounds. Both cells and exudates
provide “food” for increased microbial activity. The rhizosphere is also
an area where contaminants, which are mobile in soil but not taken up or
slowly taken up by plants and roots, will accumulate.