INTACT RHIZOSPHERE MICROBIAL COMMUNITIES USED TO STUDY MICROBIAL BIODEGRADATION IN AGRICULTURAL AND NATURAL SOILS - INFLUENCE OF SOIL ORGANIC-MATTER ON MINERALIZATION KINETICS

The rhizosphere has been shown to have a higher and more active microbial biomass than surrounding bulk soil. In agricultural and natural soils that harbor plants, this zone may affect the fate of organic chemicals in the soil. In this study, corn and soybeans were grown in an agricultural soil and a woodlot soil; the experimental chambers were designed to contain the soil and roots, but exclude the above-ground plant biomass. Controls contained soils without plants. The biodegradation of several chemicals (anionic, cationic, and nonionic surfactants) was measured. The rhizosphere generally increased initial rates of mineralization, but the total amounts mineralized were not significantly different from controls. This implies that rhizosphere microbial communities metabolize foreign chemicals at greater rates than those in the bulk soil. Since the total amounts mineralized were the same as the controls, however, biodegradation of these chemicals in soils may be limited by other soil-chemical interactions.