Effect of ryegrass (Lolium multiflorum L.) growth on degradation of benzo[a]pyrene and enzyme activity in soil

A pot experiment on soil, artificially contaminated with various benzo[a]pyrene (B[a]P), was conducted to investigate the effects of ryegrass (Lolium multiflorum L.) growth on degradation of benzo[a]pyrene and enzyme activity in soil. With and without ryegrass grown, four levels of benzo[a]pyrene (B[a]P) (0, 1, 10 and 50 mg kg^-1) were applied and soils and plants were sampled after 15, 30, 45, 60, 75, 90 and 105 days and compared with unplanted pots to study the effect of ryegrass growth on B[a]P degradation rate in soil. Results showed that ryegrass growth enhanced degradation of spiked B[a]P in the soil. In the treatments of 1, 10 and 50 mg kg^-1 B[a]P, B[a]P degradation rates in the ryegrass grown pots reached 90.3%, 87.5% and 78.6%, respectively, while in pots without ryegrass they were only 79.3%, 66.4% and 55.6%, respectively. The reason might be attributed to a bigger population size of soil microorganisms and higher soil enzymatic activities (polyphenol oxidase, dehydrogenase) due to the presence of ryegrass. In addition, the stem and leaves of ryegrass accumulated trace amounts of B[a]P, ranging from 0.43 to 1.24 mg kg^-1. Therefore, extract B[a]P by plant is not main mechanisms for remediation of B[a]P contaminated soil.