Ryegrass enhancement of biodegradation in diesel-contaminated soil

A time-course pot experiment was conducted with ryegrass grown in soil experimentally contaminated with diesel oil. Relationships among plant growth variables, microbial activity and the dissipation rate of diesel oil over time were analyzed. Results indicate that ryegrass growth can lower the dissipation threshold. The residual rate of diesel oil in the rhizosphere was 55% lower than in the corresponding root-free soil, and the threshold reduction occurred after the development of plant roots. In the rhizosphere, the number of aerobic bacteria and the amount of soil dehydrogenase activity were higher than in the root-free soil and also showed a correlation with the growth of roots. The dissipation rate of diesel oil showed a correlation with soil dehydrogenase activity in both the rhizosphere and the root-free soil. A positive correlation was observed between the growth rate of roots and soil dehydrogenase activity in the rhizosphere. Moreover, the dissipation rate per dehydrogenase activity of the rhizosphere was higher than in the root-free soil. Ryegrass roots were determined, therefore, to be effective at enhancing the biodegradation of diesel-contaminated soil. (c) 2004 Elsevier B.V. All rights reserved.