Effect of culturing ryegrass (Lolium perenne L.) on Cd and pyrene removal and bacteria variations in co-contaminated soil

Abstract Heavy metals and polycyclic aromatic hydrocarbons (PAHs) in soil pose great threat to humans and the environment, and should be strictly removed. In the present study, a plant which was suitable for growth in co-contaminated soil was investigated, then co-contaminants removal with increasing contaminants concentrations and bacteria variations in co–contaminated soil were studied. Ryegrass (Lolium perenne L.) represented higher germination rate and biomasss than tall fescue (Festuca arundinacea Schreb.), alfalfa (Medicago sativa L.) and white clover (Trifllium repens L.), when cultured on co-contaminated soil with Cd at 16.8 mg/kg and pyrene at 71 mg/kg. Co-contaminants removal was enhanced when pyrene increased from 14 mg/kg to 140 mg/kg, and inhibited when Cd injection increased more than 3.4 mg/kg. The residual pyrene in ryegrass accounted for 0.38% of its removal, indicating that pyrene biodegradation played the major role in phytoremediation rather than plant adsorption and accumulation. Planting ryegrass in co-contaminated soil increased soil bacteria total species and diversity, and changed microbial community. Specifically, the relative abundance of PAHs degrading genera Gemmatimonas, Ohtaekwangia, Luteimonas, Lacibacterium and Steroidobacter increased, which could benefite pyrene removals.