Phytoremediation of pyrene by tall fescue (Festuca arundinacea) and switchgrass (Panicum virgatum L.): Fate of pyrene and bacterial community analyses.

摘要

A growth chamber was designed to investigate the fate of PAHs (polycyclic aromatic hydrocarbons) during phytoremediation by tall fescue (Festuca arundinacea) and switchgrass (Panicum virgatum L.). For this study, 14C-labeled pyrene was used as the model contaminant and quantification of the distribution of 14C activity and pyrene concentration in different soil fractions was assessed. After 190 days of incubation, 37% and 30% of pyrene was mineralized in the soil planted with tall fescue and switchgrass, respectively, while only 4% was observed for the unplanted control. Only 8% and 9% of pyrene was recovered in the two planted treatments while there was still 32% of pyrene remaining in the unplanted control. The 14C declined significantly in all fractions except for humic/fulvic acids and the residual soils. An increased amount of pyrene/by-products was observed for all treatments and controls in the humic/fulvic fraction at the end of the experiment. This increment was higher in the control soil than in the planted soil. The amount of 14C in the residual soil remained unchanged for all treatments and controls. The most probable number of pyrene degraders was also evaluated; however, no degraders were enumerated by the end of the study. Also, PCR-DGGE analyses (polymerase chain reaction-denaturing gradient gel electrophoresis) were conducted to observe changes in the microbial community structure. There was no change in the community structure among the fresh soil and all initial and final treated soils.; A separate greenhouse study was conducted in order to monitor continuously the dynamics of the microbial community with respect to pyrene concentration and time. Soil microbial communities in both bulk and rhizosphere soils were analyzed using PCR-DGGE. However, no correlation between pyrene concentration and bacterial community shifts was observed. Even though plants significantly enhanced pyrene degradation, this was possibly accomplished by the pre-existing microbial community since no specific pyrene degraders were stimulated. The results imply that instead of the stimulation of rhizosphere microbial activity, some other mechanism may be involved in the dissipation of pyrene, such as aerating the soil or enhancing the bioavailability of the trapped contaminants. This research indicates that plants significantly increase degradation and mineralization of pyrene in soil, although evidence was not strong enough to relate any specific bacterial activity to this enhancement.