Application of engineered nanomaterials (ENMs) to soils, as either fertilizers or fungicides, has been proposed to improve the sustainability of agriculture. Although benefits of CuO NPs for plant growth have been reported, the mechanisms leading to these impacts are not well understood yet. Particularly, the link between the effect of CuO NPs on both (i) plant health and (ii) microbiome structure and function (e.g. the role of bacteria in the nitrogen cycle) needs to be investigated to engineer safer and more efficient ENMs for agriculture. The objective of this study is to quantify the influence of CuO NPs in soil on microbial structure and nitrogen cycling relevant functional genes in the rhizosphere, and to correlate these changes with plant health. In this study, Triticum aestivum was exposed to 50mg/kg CuO NPs, 50mg/kg CuSO4, or 0.5mg/kg CuSO4 in a high pH (pH =7.6) calcareous soil. CuO NP transformations in soil and uptake by plants were assessed by chemical extraction, total metal concentration and speciation measurements. The impact of the treatments on the nitrogen cycle was assessed by measuring the modification of the abundance of genes known to be implied in different steps of the nitrogen cycle, as well as the accumulation of nitrate near plant roots. DNA extraction and sequencing were performed to investigate the effect of different Cu species and concentration on the microbial structure and networking. All of these traits were measured in both the bulk soil and the rhizosphere soil (under the roots influence). The results indicate that the improvement of plant health trough Cu amendment in calcareous soil is the result of a balance between (i) Cu ionic release that will impair plant health at high concentration inducing shorter shoots and lighter roots, and (ii) total Cu concentration inducing an increase of nitrate concentration in soil, correlating with the abundance of nitrogen cycle related genes and improved plant photosynthesis. Furthermore, the statistical analysis of the microbial community changes resulting from these treatments allowed correlating gene abundance (and thus N-related soil function) with the occurrence of specific genera. This study thus identified the bacterial genera that were responsible for the improved nitrate accumulation in the wheat rhizosphere. This opens the door to the design for nano-agrochemicals that would enhance plant health through soil function improvements.

CuO NPs improve plant health in high pH (calcareous) soils by affecting microbiome structure, network, and nitrogen-related functions

2019 Spring National Meeting

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