Interactive Effects of Plants and Metal Oxide Nanoparticles on Soil Bacterial Communities.

Engineered nanoparticles (ENPs) are expected to enter agricultural soils, likely through land application of biosolids. The potential adverse effects of ENPs have been studied on food crops and soil bacterial communities separately; however, how ENPs will affect the interacting plant-soil system remains unknown. To address this, we assessed ENP effects on microcosms planted with soybeans and evaluated how the presence of the plant influenced the effects of ENPs on microbial communities. Microcosms were exposed to different doses of nano-CeO₂ (0, 0.1, 0.5, and 1.0 g kg^-1) or nano-ZnO (0.05, 0.1, and 0.5 g kg^-1). Bacterial community shifts were analyzed by both terminal restriction fragment length polymorphism (T-RFLP) and PhyloChip. Nano-CeO₂ did not affect soil bacterial communities in unplanted soils, but 0.1 g kg^-1 nano-CeO₂ moderately altered soil bacterial communities in planted soils. In contrast, nano-ZnO at 0.5 g kg^-1 significantly altered soil bacterial communities, increasing some (e.g., Rhizobium and Sphingomonas) but decreasing other (e.g., Ensifer, Rhodospirillaceae, Clostridium and Azotobacter) operational taxonomic units (OTUs). There were fewer sensitive OTUs to nano-ZnO in planted (41), versus unplanted (85), soils, suggesting that plants ameliorate the toxic effects of some ENPs (ZnO) on soil bacterial communities, and may mediate ecosystem impacts of other ENPs (CeO₂).