Dissipation Behavior Of Polvcvclic Aromatic Hydrocarbons In Rhizosphere Of PAHs-Tolerant And-Sensitive Rice Cultivars And Microbial Mechanism Involved

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent organic compounds in environment. PAHs show an accumulation trend in soils because of their persistence and difficulty in degradation. Soil contamination with PAHs poses a great threat to the production and ecological function of soil, the food quality and human health. So the behaviors of PAHs in environment and their remediation technologies have received an increase concern. Rhizoremediation is one of the most potential remediation technologies, combined by plant and microbes processes. Based on the rice cultivars screening experiment, we tried to investigate the specific dissipation behaviors of PAHs and the microbiological mechanisms. The results were as followed:(1) Agar culture was used to determine the the effects of PAHs on the root length and biomass (dry weight) of ten rice cultivars. The root elongation and biomass of Ⅱ youming86and Xiushui134cultivars was remarkably suppressed by PAHs contamination (p<0.05). Meanwhile, PAHs stress had no significant influences on the root elongation and biomass of Fengyou22, Zheyou12and Huanghuazhan (p>0.05). Thus, we determined Ⅱ youming86and Xiushui134cultivars were sensitive to PAHs contamination, and Fengyou22, Zheyou12and Huanghuazhan were insensitive to PAHs contamination.Huanghuazhan and Ⅱ youming86cultivars were used to detect the root uptake of PAHs from water and the influences of Fe2+on the root uptake. Fe2+facilitated the absorption/adsorption of PAHs by roots. At days2and4, the concentrations of phenanthrene and pyrene in the roots of PAHs-tolerant cultivars (Huanghuazhan) were significantly higher than the roots of PAHs-sensitive cultivars (Ⅱ youming86). Huanghuazhan had fast metabolism ability of PAHs, then at day7, the concentrations of phenanthrene and pyrene in the roots of Huanghuazhan were significantly lower than the corresponding roots of Ⅱ youming86. Regarding Ⅱ youming86, the treatment of Fe2+had the highest accumulated amounts of phenanthrene and pyrene in the whole experiment time.(2) A greenhouse experiment was conducted in the PVC pots fixed with rhizobags to investigate the differentiation of PAHs dissipation in aerobic-anaerobic interface induced by the rhizosphere of PAHs-tolerant and-sensitive rice(Oryza sativa L.) cultivars. The spiked phenanthrene and pyrene had least influences on the biomass and root activity of Huanghuazhan grown in soil1. The dissipation of phenanthrene in rhizosphere soils exhibited no significant differences with those in non-rhizosphere. The dissipation of pyrene in rhizosphere soils was significantly accelerated in rhizosphere produced by both rice cultivars in both soils at day30after transplanting, but the differences became negligible with increase of cultivation time. Ⅱ Youming86grown in soil1made pyrene have the highest dissipation rate.(3) PAHs stress significantly reduced the biomass of microbes and some signature groups at the initial30days, but the decrease disappeared at day60after transplanting. Rhizosphere microbial responses under PAHs stress varied among soil properties, rice cultivars and rice growing time. Eight individual PLFAs (i16:1H,16:lco5c,18:0(10Me), cy19:0ω8c,16:1ω7c, a15:0,12:03OH and19:1ω11c) had remarkable relationship with PAHs dissipation. The fungi was the most important microbial group stimulated by PAHs stress in rice rhizosphere and in turn facilitated the dissipation of PAHs in both soils. Meanwhile, dissolved organic carbon (DOC) also had a great impact on PAHs dissipation in soils.