Interaction of Cd/Zn hyperaccumulating plant (Sedum alfredii) and rhizosphere bacteria on metal uptake and removal of phenanthrene

The effects of bacteria (Burkholderia cepacia) on plant growth, metal uptake, tolerance index and phenanthrene degradation by a hyperaccumulating plant (Sedum alfredii) were investigated. It was found that inoculation of bacteria did not enhance plant growth and metal uptake; while both metal translocation factor (up to 84% for Cd and 42% for Zn) and tolerance index (up to 23.2% for shoot and 72% for root) were significantly increased. In addition, inoculation of bacteria also alleviated the reductions of bioaccumulation factor and phytoextraction efficiency of As, Cu and Zn with the increasing proportions of polluted soil applied, while they were even increased for Cd and Pb (up to 31.2 and 124%, respectively). Up to 96.3% of phenanthrene was removed in the treatment with both plant and bacteria at the end of the experiment. A positive correlation between metal and P accumulation in plants was observed, it is suggested that high P uptake is directly involved in metal detoxification and leading to an increased P requirement. With the assistance of bacteria, S. alfredii could be able to withstand higher metal concentrations and it could also provide a practical tool for phytoremediation.