Biodegradation of fuel oil hydrocarbons in the rhizosphere of maize

Plant roots provide suitable habitats fur the growth of microorganisms. Par ticularly, the release of exudates by living roots enhances the microbial a ctivity in the rhizosphere. This work was undertaken in the laboratory to s tudy the biodegradation of fuel oil hydrocarbons (HC) in the presence of gr owing plants and to assess the effects of root exudates on biodegradation, Maize (Zen mays L.) plants were grown in soil microcosms for 120 d and in l iquid (hydroponic) cultures for 40 d in presence and in absence of fuel oil added at slightly phytotoxic concentrations (soil: 3300 mg kg(-1); hydropo nic cultures: 850 mg L (1)). Controls without plants permitted the quantifi cation of the rhizosphere effects on WC removal. Concentration and chemical composition of residual HC were periodically determined, Higher degradatio n rates of saturated and aromatic HC were observed in soil in the presence of plants in the early stages of biodegradation when maize growth was expon ential. No significant change was observed in the polar fraction. After 120 d, the biodegradation rates were identical in the presence or absence of p lants. In hydroponic conditions, a stimulation in the degradation of satura tes was observed until Day 40. No significant difference was detected in th e aromatic fraction. The faster biodegradation of HC in the presence of pla nts was attributed to the changes in environmental renditions in the rhizos phere; e.g., increase of I-IC bioavailability, stimulation of bacterial pop ulations due to plant exudation and effects on physical properties of soil. Competition for mineral nutrients between plants and microorganisms was sh own.