Interactions between plants, contaminants and microorganisms during the phytoremediation of diesel contaminated soil.

摘要

This thesis is an investigation of some interactions occurring in the rhizosphere during the phytoremediation of petroleum hydrocarbons with the goal of understanding the mechanisms involved.; After the selection of Perennial ryegrass and alfalfa using an acute plant toxicity bioassay, I wished to determine the effects these plant species had on the microbial community and more specifically on the petroleum degrading community. Results indicate that plants alter the soil indigenous microbial community and that different plants exert different effects on the degrading microbial community.; It had been suggested in the literature that arbuscular mycorrhizal fungi (AMF) may play an indirect role in the phytoremediation of organic contaminants by their effect on plant establishment, stress tolerance and nutrient acquisition as well as by increasing the volume of soil being remediated. I therefore attempted to examine the role that a plant, a mixed microbial inoculum and an AMF inoculum, alone and together, may have on the degradation of diesel in soil. The results of this study were inconclusive and further support the notion that interactions that are occurring in the rhizosphere are complex and difficult to study and understand.; The colonization of P ryegrass by Glomus intraradices, the AMF species studied, during the degradation study was lower then expected, I therefore wanted to study the effects of petroleum products on the growth and development of G. intraradices. I found that germination of G. intraradices spores was not affected by the presence of F2 heating diesel oil and HAGO oil, but was reduced by Esso automobile diesel. Germ tube elongation was not affected by the presence of F2 heating diesel oil or HAGO oil, unless a plant root was present. It was not clear if this growth inhibition was caused by the toxicity of the petroleum products to hyphal growth or if diesel was interfering with the communication between plant and fungus. I therefore continued investigating the plant/AMF/contaminant interactions using plant root exudates obtained from transformed carrot root not exposed to diesel. I wanted to determine if diesel was interfering with the mobility of root exudates or the recognition of these by G. intraradices . Results of this study indicate that the movement of root exudates in vitro are not hindered by the presence of diesel and that G. intraradices can recognize plant signals in the presence of diesel. Therefore, the reduction in growth seen in the previous experiment could be a result of direct toxicity of diesel to the fungus or of alteration of root exudates by diesel, thereby altering the signals contained in the exudates.; The results obtained during the course of my PhD research contribute knowledge to the interactions and mechanisms involved in the rhizoremediation of petroleum-contaminated soil. It is important to understand these interactions so that we can improve the efficacy of the phytoremediation system.