Biodegradation of fuel oil hydrocarbons in the rhizosphere of maize

Plant roots provide suitable habitats fur the growth of microorganisms. Particularly, the release of exudates by living roots enhances the microbial activity in the rhizosphere. This work was undertaken in the laboratory to study the biodegradation of fuel oil hydrocarbons (HC) in the presence of growing 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 liquid (hydroponic) cultures for 40 d in presence and in absence of fuel oil added at slightly phytotoxic concentrations (soil: 3300 mg kg(-1); hydroponic cultures: 850 mg L (1)). Controls without plants permitted the quantification of the rhizosphere effects on WC removal. Concentration and chemical composition of residual HC were periodically determined, Higher degradation 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 exponential. No significant change was observed in the polar fraction. After 120 d, the biodegradation rates were identical in the presence or absence of plants. In hydroponic conditions, a stimulation in the degradation of saturates was observed until Day 40. No significant difference was detected in the aromatic fraction. The faster biodegradation of HC in the presence of plants was attributed to the changes in environmental renditions in the rhizosphere; e.g., increase of I-IC bioavailability, stimulation of bacterial populations due to plant exudation and effects on physical properties of soil. Competition for mineral nutrients between plants and microorganisms was shown.