The impact of various forms of silver nanoparticles on the rhizosphere of wheat (Triticum aestivum L.) - Shifts in microbiome structure and predicted microbial metabolic functions.

The study investigated the effects of different silver nanoparticles (AgNPs) on the soil microbiome and wheat growth. For comparison purposes, a commercial fungicide and silver nitrate (AgNO) were used. The results revealed three distinct groups of nanoparticles based on their impacts. Small-size AgNPs (10 nm) with a negative charge, as well as fungicide had limited effects on the microbiome, similar to the no-treatment control. Bigger in size (30-60 nm) and a negative charge AgNPs showed the most beneficial effects on soil microbiota shifts. These AgNPs increased the abundance of bacteria with beneficial traits such as nitrogen-fixing, urease, protease, and lignin degradation bacteria. The third type of AgNPs had a positive charge of nanostructure and influenced specific microbial populations, increasing the abundance of anaerobic and autotrophic groups of microorganisms, which could be assessed as a harmful shift for plants growth promotions and was similar to the AgNO treatment. Overall, the study emphasized the potential of AgNPs in agriculture not only as biocidal. The conducted study proved that AgNPs with bigger size/negative charge, used in low concentration can have a surprisingly stimulating effect on the positive characteristics of the rhizosphere microbiome. Moreover, the surface charge of AgNPs is a significant factor affecting microbial activity of wheat rhizosphere soil, which in this treatment is significantly similar to the AgNO treatment.