INFLUENCE OF PLANT ROOT EXUDATES ON MICROBIAL POPULATIONS
Ken Yoshitomi and Jodi Shann
Department of Biological Sciences, University of Cincinnati, 614 Rieveschl, P.O. Box 210006, Cincinnati, OH 45221-0006; Phone: (513) 556-9765, E-mail: .
Phytoremediation has been investigated as a cost-effective option for the clean up of contaminated soils. Although numerous studies have demonstrated increased degradation of hazardous organic compounds in the soil surrounding plant roots (the rhizosphere), little is known about the basic mechanisms contributing to this phenomena. In this study, the role of root exudates was explored. Specifically, the influence extracted plant exudates have on soil microorganisms.
Corn (Zea mays L.) was grown in a hydroponic apparatus designed to simulate soil while maintaining aseptic conditions. Soluble root exudates were allowed to flush through the system and over soil columns. Microbial characterization of the soil columns was assessed by plate counts, microbial lipid analysis of biomass and activity, and their ability to mineralize a radiolabeled PAH, pyrene. Community shifts in their carbon source utilization profile were determined by Biolog™ GN analysis.
Results from the exudate amendment studies indicated that long-term application of exudates to bulk soil was able to enhance the microbial populations’ potential to mineralize 14C-pyrene. However, stimulation of biomass and activity was minimal, suggesting that mere numbers or activity was not responsible for the increased mineralization. Multivariate analysis of Biolog™ GN plates revealed functional shifts in microbial communities between treatments. This data suggests exudate pressures may change the functional aspect of the community structure, favoring degrading populations of bacteria.
Current studies are further investigating the root exudate phenomena by addressing the influence of extracted root exudates on two different degrading genera of bacteria, a gram negative and a gram positive. Typically associated with different portions of the soil (rhizosphere vs. bulk soil), their responses to plant root exudates will help elucidate the role these exudates play for different types of bacteria. These studies will give a clearer understanding of the potential mechanisms controlling rhizosphere degradation.
Key words: Zea mays, root exudates, 14C-pyrene