The polycyclic aromatic hydrocarbons (PAHs) is a widespread environmental pollutant that seriously threats soil health, human life and ecosystems. PAHs and heavy metals enter the soil via sewage irrigation, solid waste treatment, transportation, and industrial activities, and then form composite pollutants through the progressive accumulation. PAHs and heavy metals are carcinogenic, mutagenic and teratogenic, and can persist in the soil for a very long time. In recent decades, the composite pollution of PAHs and heavy metals becomes more and more serious in China, and attracts widespread attention. Plant remediation, or phytoremediation, is widely recognized as a low-cost and high-efficiency technology. It doesn't produce secondary pollution, and can be applied in a wide range of settings. Microbes with special functions in the plant rhizosphere participate in the degradation of soil pollutants. But different types of pollutants affect the complex interactions between plants and rhizosphere microbes and thus the remediation potential of certain plants. A deep understanding of such interactions may improve phytoremediation efficiency.

DAI Yuanyuan, LIU Rui and their colleagues from the Pollution Ecology and Environmental Ecology Engineering Research Center at the Institute of Applied Ecology, Chinese Academy of Sciences, conducted a pot planting experiment in a growth chamber. They examined the remediation effects of a Fescue species, Fire Phoenix, on PAHs-Cd contaminated soil, and the responses of rhizosphere soil enzyme activity and bacterial communities.

For the soil with low concentration PAHs, the 150-day phytoremediation removed 64.57% of PAHs and 40.93% of Cd in the soil, and the change in dehydrogenase (DHO) activity showed significantly positive correlations with the removal rates of PAHs and Cd. For the high-PAHs soil, the corresponding removal rates of PAHs and Cd were 68.29% and 25.40%, respectively. The polyphenol oxidase (PPO) activity decreased in the soil with plant grown compared to the soil with no plant. Continuous changes in bacterial communities were detected during the plant remediation process, and the changes were particularly pronounced in the soil with low PAHs concentrations. The plant promoted the growth of Mycobacterium, Dokdonella, Gordonia and Kaistobacter, which played important roles in PAH degradation or Cd dissipation. The results show that Fire Phoenix can effectively stimulate soil enzymes and bacterial communities which in turn enhance the remediation effects on PAHs-Cd contaminated soil.