Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously distributed throughout the environment, representing a challenge for environmental scientists and decision makers. As soil constitutes a natural sink for contaminants, the control and management of contaminated soil has been the focus of multiple investigations since the last quarter of the 20th century. Within the different approaches that have been developed for this purpose, the use of plants for the remediation of contaminated soil can be considered as a promising technology given its overall low cost and general public acceptance. Although this technology has been studied for over 30 years, the specific mechanisms behind the process have not been fully understood yet. Therefore, the aim of this thesis was to investigate the impact of plant root biomass and components typically found within root exudates on the biodegradation and bioaccessibility of phenanthrene from soil with particular interest in the study of root-induced changes of hydrocarbon bioaccessibility. Results showed that microbial catabolism and biodegradation of 14C-phenanthrene can be promoted by the incorporation of plant roots into the soil, with significant effects most likely to be observed after an adaptation period. Moreover, although chemically assessed bioaccessibility of 14C-phenanthrene was not observed to be affected by root biomass or organic acids typically found within root exudates, the use of high concentrations of citric and malic acid were observed to promote lager desorbable fractions of the hydrocarbon. This thesis contributes evidence supporting the role of root decay, turnover and exudation for the biodegradation of PAHs in contaminated soil as defining mechanisms by which plants can promote the biodegradation of this type of contaminants.