Moderate Input of Nanoscale Zero-Valent Iron Accelerated Soil Polychlorinated Biphenyls Dissipation with Limited Inhibition on Arbuscular Mycorrhizal Fungal Diversity

Nanoscale zero-valent iron (nZVI) could degrade chlorinated pollutants like polychlorinated biphenyls (PCBs), but may be toxic to soil beneficial microbes such as arbuscular mycorrhizal (AM) fungi. The purpose of this work was to investigate the changes in community structure and diversity of AM fungi in PCBs-contaminated soils in response to input of nZVI, focusing on the balance between PCB dissipation and AM fungal conservation. Both PCBs-amended (10 mg/kg Aroclor 1242, a PCB mixture) and control soils with three nZVI input levels (0.1, 1, and 10 g/kg) were tested in this 8-week incubation experiments. Soil pH and available P and PCB concentrations were determined, and the nested PCR amplification of the 18S rRNA gene of AM fungi was performed and sequenced on the Illumina MiSeq™ platform. Differences in soil AM fungal community structure were compared using principal component analysis (PCA). The redundancy analysis (RDA) was used to reveal the relationship between PCBs, soil properties, and AM fungal communities under different treatments. Soil available P concentration significantly decreased as the nZVI input level increased, but only the high input level (10 g/kg) induced significantly higher soil pH and lower richness and Shannon and Simpson’s indices of AM fungal communities compared to the low input case (0.1 g/kg). The presence of PCBs only led to differentiation in AM fungal communities in the low nZVI input case. In the PCBs-amended soils, both moderate (1 g/kg) and high input of nZVI significantly decreased the concentrations of di-, tri-, tetra-, penta-chlorinated biphenyls and total PCBs compared to the low input case, while the high input level only further significantly increased the dissipation of hexachlorinated biphenyls compared with the moderate input case. nZVI with high adsorption effects on soil available P had greater impacts on soil AM fungi than PCBs. However, the moderate nZVI input level (1 g/kg) had no significant effects on the richness and diversity indices of AM fungal community compared to the low input case (0.1 g/kg) and seemed to be more suitable for remediating of PCBs-contaminated soils, focusing on the limited inhibition on AM fungi.