Citation:

Reichman, J., M. Slattery, Mark G. Johnson, C. Andersen, AND S. Harper. CeO2 nanoparticle dose and exposure modulate soybean development and plant-mediated responses in root-associated bacterial communities. Scientific Reports. Nature Publishing Group, London, Uk, 14:10231, (2024). https://doi.org/10.1038/s41598-024-60344-8

Impact/Purpose:

Engineered nanoparticles (ENMs) have been recognized as valuable components of new technologies and are currently being used in a variety of consumer products due to their unique physical, chemical, and electrical properties. The properties that make these particles functionally unique also may influence their toxicity to organisms in soils and ecosystems. CSS’s Emerging Technologies research is designed to identify potential adverse effects of these materials in the environment, including toxicity to various components of agricultural ecosystems. To gain better understanding of how ENMs affect microbial dynamics in agricultural soils, we examined the influence of nano-sized CeO2 particles (nCeO2) on root-rhizosphere communities and whether nCeO2 exposure altered growth, nodule development and reproductive output of soybean. As a further test of ENM aging in soils, one treatment included adding nCeO2 to the soil 3 months prior to planting soybean seed. Soybeans were grown to maturity in a natural soil with either aged nCeO2 (3-month incubation in soil) or pristine un-aged nCeO2 (no incubation in soil) at environmentally realistic exposure levels (1 mg kg-1) or at elevated levels (100 mg kg-1). Soil microbiome analysis was performed on three distinct rhizosphere zones around soybean roots. Soybeans yield and biomass decreased in response to nCeNP exposures, particularly among the pristine, low treatments. To assess the relevance of the root-associated microbiome in soybean responses, root samples were processed for 16S rDNA amplicon sequencing. The root microbiome structure shifted dramatically in the un-aged pristine nCeNP exposures, whereas the aged nCeO2 communities were more similar to the control. However, aged treatments caused a significant loss of bacterial richness when compared to the control, and the magnitude of these effects was dependent on spatial proximity to the root surface. Overall, both the concentration and the age of nCeO2 were relevant factors that affected the impacts to soybeans and their root-associated microbiome. In this experiment, environmentally relevant concentrations of nCeO2 produced agriculturally and ecologically relevant changes in a commercially important crop species. Additional studies are underway to determine the role of rhizosphere microbial communities in affecting availability and uptake of ENMs into plants and the possibility of ENM entry into the human food chain.

Description:

Agricultural soils are increasingly undergoing inadvertent and purposeful exposures to engineered CeO2 nanoparticles (NPs), which can impact crops and root-associated microbial communities. However, interactions between NP concentration and exposure duration on plant-mediated responses of root-associated bacterial communities are not well understood. Soybeans seedlings were grown in soil with uncoated NPs added at concentrations of 0, 1 or 100 mg kg−1. Total soil exposure durations were either 190 days, starting 106 days before planting or 84 days with NP amendments coinciding with planting. We assessed plant development, bacterial diversity, differential abundance and inferred functional changes across rhizosphere, rhizoplane, and root tissue compartments. Plant non-monotonic dose responses were mirrored in bacterial communities. Most notably, effects were magnified in the rhizoplane under low-dose, short-exposures. Enriched metabolic pathways were primarily related to biosynthesis and degradation/utilization/assimilation, rather than responses to metals or oxidative stress. Our results indicate that plant-mediated bacterial responses were greater than direct NP impacts. Also, we identify needs for modeling non-monotonic legume stress responses that account for coinfection with mutualistic and parasitic bacteroids. Our findings provide new insights regarding effects of applications of soil amendments such as biosolids containing NPs or nano-enabled formulations used in cultivation of legumes and other crops.

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