Co-transformation of HMs-PAHs in rhizosphere soils and adaptive responses of rhizobacteria during whole growth period of rice (Oryza sativa L.)

Abstract

This study investigated the transformations of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in rhizosphere soils and adaptive responses of rhizobacterial community under the real field conditions during four growth stages (e.g., greening, tillering, heading, and maturity) of early rice (Zhongjiazao 17) and late rice (Zhongyou 9918) in Jiangshe village (JSV) and Yangji village (YJV). Results showed that rhizosphere soils of YJV were mildly polluted by Cd and PAHs compared to that of JSV. The relative abundance of bioavailable Cd (bio-Cd) and bioavailable As (bio-As) in rhizosphere soil increased before the heading stage but decreased at the subsequent growth stage, but the content of ΣPAHs in rhizosphere soil decreased gradually during whole growth period. The dominant rhizobacteria genera at YJV (e.g., Bacillus, Massilia, Sphingomonas, and Geobacter) increased at an abundance level from the tillering to heading stage. Rhizobacteria interacted with the above co-pollutant more intensely at the tillering and heading stage, where genes involved in HM-resistance and PAH-degradation appeared to have a significant enhancement. The contents of bio-Cd and bio-As in rhizosphere soil of early rice were higher than that of late rice at each growth stage, especially at the heading stage. Bio-Cd, ΣPAHs, and organic matter were key factors influencing the community structure of rhizobacteria. Results of this study provide valuable insights about the interactions between HM-PAH co-pollutant and rhizobacterial community under real field conditions and thus develop in-situ rhizosphere remediation techniques for contaminated paddy fields.