Unlike animals,plants need nutrients in simple,inorganic and ionic forms.Thus,plants cannot use immobilized nutrients until they have been changed to simple,inorganic forms by microbial decomposers.This process is called mineralization,and the microbes that do this are abundant in the rhizosphere.Immobilization and mineralization are opposite processes (figure 5-7).The sulfur cycle is an example of these processes (figure 5-8).