Dissipation gradient of pyrene in the rhizosphere of Potamogeton crispus L.

In this study, a self-designed laminar rhizobox divided into six separate compartments was used to investigate the degradation gradient of pyrene in the rhizosphere of submerged aquatic plant Potamogeton crispus L. (P. crispus). At the end of a 30-day experiment, P. crispus significantly increased the dissipation of pyrene by 16.7-24.5% within the distance of 4 mm from root surface. Concentrations of 1-OH-pyrene, a hydroxylated metabolite of pyrene, were 1.4-15.5 times higher in unplanted treatment than in planted treatment and were positively correlated to pyrene concentrations. At the same time, aerobic bacterial biomass indicated by phospholipid fatty acid content and polycyclic aromatic hydrocarbon (PAH)-degrading bacterial population were both significantly enhanced by P. crispus within the distance of 8 mm from root surface. Sediment redox potential within the distance of 5 mm from root surface was also obviously improved. Pearson analysis indicated that dissipation ratios of pyrene were positively correlated to PAH-degrading bacterial populations and aerobic bacterial biomasses. Based on the rhizosphere gradient zones of different parameters influenced by P. crispus as well as the correlation analysis, it could be concluded that oxygen is the limiting factor in remediating pyrene in sediments.