BIODEGRADATION OF PHENOL, 2,4-DCP, 2,4-D, AND 2,4,5-T IN FIELD-COLLECTED RHIZOSPHERE AND NONRHIZOSPHERE SOILS

This study investigated xenobiotlc biodegradation in rhizosphere soil collected from field-grown plants, grouped for analysis as monocots or dicots. Microbial activity was highest in monocot rhizosphere soils, followed by dicot rhizosphere soils and, finally, nonrhizosphere soils. No differences were seen between these soils in the mineralization of phenol or 2,4-dichlorophenol (2,4-DCP), but there were differences in 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) mineralization. The rate constants for 2,4-D or 2,4,5-T mineralization in nonrhizosphere soil were lower than those for either rhizosphere soil. Monocot rhizosphere soil mineralized these compounds faster than dicot rhizosphere son. Thus, soils that had a prior association with a plant showed significantly increased rates of mineralization for the more recalcitrant compounds tested. In addition, this enhanced mineralization in the rhizosphere appeared to be dependent on the type of plant involved.