3.4. PAH-degrading bacterial population in sediments
Plants were reported to have a positive effect on the number of cultivable PAHs degraders in soils, which is related to the promoting impact of plants on PAHs dissipation (Ma et al., 2010). In this study, PAH-degrading bacterial populations in sediments under different treatments are shown in Fig. 3. PAH-degrading bacterial population increased with increasing plant density at the initial period (i.e., the first 18 days), but thereafter, variation of PAH-degrading bacterial population was observed. In the treatment of 260 and 780 plants m2, PAH-degrading bacterial population generally increased during the remaining 36 days, whereas opposite trend could be found in the treatment of 2080 plants m2. At the end of the experiment, the difference of PAH-degrading bacterial population among different plant densities was not significant (p > 0.05) except lower PAH- degrading bacterial population in the treatment of 260 plants m2.