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      The relationship between plants and their root-associated microbial communities in hydrocarbon phytoremediation systems

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      Date
      2008-04-30
      Author
      Phillips, Lori (Lori Ann)
      Type
      Thesis
      Degree Level
      Doctoral
      Metadata
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      Abstract
      Phytoremediation systems for petroleum hydrocarbons rely on a synergistic relationship between plants and their root-associated microbial communities. Plants exude organic compounds through their roots, which increase the density, diversity and activity of plant-associated microorganisms, which in turn degrade hydrocarbons. Understanding the mechanisms driving this relationship poses one of the more intriguing challenges in phytoremediation research. This study was designed to address that challenge. Plant-microbe interactions in a weathered-hydrocarbon contaminated soil were examined under controlled growth chamber, and field conditions. In both environments single-species grass treatments initially facilitated greater total petroleum hydrocarbon (TPH) degradation than Medicago sativa (alfalfa), mixed species, or control treatments. In growth chamber studies increased degradation was linked to increased aliphatic-hydrocarbon degrader populations within the rhizosphere. Under field conditions, specific recruitment of endophytic aliphatic-hydrocarbon degraders in response to high TPH levels may have facilitated increased degradation by the grass Elymus angustus(Altai wild rye, AWR). AWR stably maintained these communities during times of local drought, enabling them to act as subsequent source populations for rhizosphere communities. The broad phylogenetic diversity of AWR endophytes, compared to the Pseudomonas-dominated communities of other plants, contributed to the observed stability. The relative composition of exudates released by plants also impacted both degradation activity and potential. Alfalfa released higher concentrations of malonate, which hindered degradation by decreasing metabolic activity and concomitantly inhibiting catabolic plasmid transfer. In contrast, AWR exudates contained high levels of succinate, which was linked to increased catabolic gene expression and plasmid transfer. A reciprocal relationship between exudation patterns and endophytic community structure likely exists, and both parameters have a specific influence on rhizosphere degradation capacity. In this study, grasses were more successful in maintaining the specific balance of all parameters required for the transfer, preservation, and stimulation of hydrocarbon catabolic competency.
      Degree
      Doctor of Philosophy (Ph.D.)
      Department
      Soil Science
      Program
      Soil Science
      Supervisor
      Greer, Charles W.; Germida, James J.
      Committee
      Reynolds, C. Mike; Korber, Darren R.; Knight, J. Diane; Farrell, Richard E.; Ross, Andrew R. S.
      Copyright Date
      April 2008
      URI
      http://hdl.handle.net/10388/etd-10282008-162403
      Subject
      Phytoremediation
      Plant root exudates
      Microbial community assessment
      Petroleum hydrocarbon
      Plant root endophytes
      Bioremediation
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