Effect of plant-growth-promoting rhizobacteria on phytoremediation efficiency of Scirpus triqueter in pyrene-Ni co-contaminated soils

The aim of this study was to investigate whether the plant-growth-promoting rhizobacteria (PGPR) could enhance phytoremediation efficiency of Scirpus triqueter (S.triqueter) in the pyrene-Ni co-contaminated soil. We also expected to reveal the possible mechanism for the affected phytoremediation efficiency induced by PGPR. We used three kinds of contaminated soils (Ni-contaminated soil, pyrene-contaminated soil and pyrene-Ni co-contaminated soil) to conduct this pot study. After harvest, plants growth indicators, polyphenol oxidase (PPO) activity and soil microbial community structure of each treatment were investigated to explain the different dissipation rates of pyrene and removal rates of Ni between treatments with and without PGPR. The results showed that PGPR-inoculated S. triqueter increased dissipation rates of pyrene and removal rates of Ni in all three contaminated soils, among which Ni removal rates in Ni single contaminated soil was elevated most significantly, from 0.895‰ to 8.8‰, increasing nearly 9 folds. However, Ni removal rate efficiency in co-contaminated soil was weakened because more toxic and complicated co-contaminated soil restrained plant growth and Ni absorption. We also observed that co-contamination harmed the soil microbial community more severely than that in single pyrene or Ni contaminated soil through phospholipid fatty acids analysis. Furthermore, dissipation rates of pyrene and removal rates of Ni were found positively correlated to the PPO activity and the abundance of branched and saturated fatty acids reflected by Pearson correlation analysis.