The maize microbiome warns for unintended effects of nanosilver application in agriculture

Abstract

Agriculture is constantly in development, driven by the ever increasing world population and the need for green energy. This stimulates the development of new techniques and substances which could be of use for agricultural growth. One such substance is nanosilver, an offspring of the marriage between silver’s welldocumented antimicrobial properties and nanotechnology which increases the applicability and efficiency of these properties. Nanosilver is applied purposely on agricultural fields to prevent and counteract phytopathogen infections. It is sprayed on plant shoots, leading to voluntary aboveground exposure of the plants but also unavoidable unvoluntary build up in soil and therefore belowground exposure. Accumulation in soil is increased by urban run-off and biosolid application due to the myriad of urban nanosilver applications. Next to the desired effect of counteracting phytopathogens, this exposure of crops to nanosilver is likely to also produce side effects. The toxicity toolkit of nanosilver is strong because of its variety: nanosilver binds to nucleophilic amino acids, and therefore interferes with various proteins and compounds, leading to ROS production, DNA damage and other harmful processes. Hydroponics studies showed that nanosilver can be toxic to plants, as well as to beneficial and maleficent (phytopathogenic) microorganisms which are naturally associated with plants. Predicting nanosilver’s impact in the field from these in vitro studies is impossible, because of the highly complex and interactive nature of the biological system. Nanosilver interacts with soil particles, leading to an unknown concentration of mobile and active nanosilver. Additionally, all effects aboveground and belowground on the plant and its microbiome take place simultaneously. The interaction between these organisms and the individual effect of nanosilver on each of them decide how crops react. Hence, in order to understand the full impact of nanosilver in agricultural fields, these processes should be individually dissected and the gathered information consequently assembled into a complete image. Therefore, in this PhD study we investigate the impact of nanosilver exposure on maize, the third leading crop worldwide, and its associated microbiome in soil-based studies. By focusing in detail on the multiple processes taking place, we aim to develop a multi-level understanding of nanosilver’s agriculture as well as to gather more information on the complex interactions between plants and their microbiome.