Interplay between biological nitrification inhibitors, nitrogen cycling and agronomic nitrogen use efficiency

Each year, humans apply enough industrially produced nitrogen-based fertilizer, to effectively double the input of bioavailable nitrogen in the environment. This has allowed for a massive increase in food production during the 20th century (green revolution) and is necessary to nutritionally sustain the global population. Currently, about half of humanity is dependent on food that could not have been produced without industrial nitrogen fertilization. However, the additional input of reactive nitrogen into the environment has also caused a massive unbalancing of the natural nitrogen cycle that led to devastating ecological consequences. Excessive or ill- designed nitrogen fertilization regimes cause the emission of large amounts of nitrous oxide - a greenhous e gas 300 times more potent than carbon dioxide - from cropped fields. In addition, it also leads to mas s ive pollution of aquatic environments with nitrate, and contributes to a major problem for the health of the planet known as eutrophication. Nitrogen-based agricultural fertilizers are most often applied in the form of ammonia or urea. However, crops compete with microorganisms in the soil for these nitrogenous compounds. Some groups of microorganisms (nitrifiers and denitrifiers) transform the added nitrogen fertilizer, and their activity leads to large fertilizer loss by the production of gaseous compounds like nitrous oxide and by nitrate formation that is easily washed out from soils. Current methods to inhibit soil nitrification as the primary cause of nitrogen fertilizer loss often involve the use of synthetic nitrification inhibitors (SNIs) that are applied to agricultural fields alongside fertilizers. However, many SNIs are short lived and have unknown effects on the broader soil microbial community and plants. Moreover, their effect on humans and animals is largely unknown. In this research project, we aim to identify and extensively characterize plant-derived biological nitrification inhibitors (BNIs). We hypothesize that by inhibiting soil nitrific ation with BNIs we can increase the nitrogen retention in agricultural soils and plant nitrogen use efficiency. In this research project, we take an interdisciplinary approach from various fields within the life sciences to identify and characterize natural, plant - derived BNIs. We will utilize cutting edge technologies in the fields of plant chemistry, microbial physiology, and biogeochemistry to create a holistic view of the impact of BNIs on the health of plants and the soil microbiome. This innovative research project will be a collaborative effort between researchers from the University of Vienna and the University of Natural Resources and Life Sciences, Vienna.

Industrial agriculture has significantly increased the availability of bioavailable nitrogen in soils, enabling the food production that currently feeds about half of the world's population. At the same time, this high nitrogen input has caused serious environmental problems: large emissions of nitrous oxide, a greenhouse gas approximately 300 times more potent than CO, as well as widespread contamination of groundwater, rivers, and oceans with nitrate, which contributes to global eutrophication. A substantial part of these nitrogen losses results from the activity of soil microorganisms, which convert nitrogen into forms such as nitrate or nitrous oxide that are easily lost from the soil. To reduce these losses, synthetic nitrification inhibitors (SNI) are commonly used. SNIs act over long periods, effectively suppressing nitrification, but they can persist in the soil and potentially affect other microbial processes. In our project, we investigated plant-produced biological nitrification inhibitors (BNI) as a natural alternative. BNIs act in a targeted manner, degrade relatively quickly in the soil, and show minimal or no negative effects on other important microbial processes. This allows them to function specifically when nitrogen fertilizer is applied, without accumulating in the soil over time-a key advantage over synthetic inhibitors. Our results showed that the effectiveness of BNI depends strongly on soil type. In some soils, BNI were less effective, while in others they inhibited nitrification to a similar degree as established synthetic inhibitors. This demonstrates that BNI can, under suitable conditions, significantly reduce nitrogen losses and improve fertilizer efficiency without negatively affecting soil ecosystems. Throughout the project, we combined molecular, metabolomic, microbiological, and soil ecological approaches to identify different BNI and their degradation products, clarify their mechanisms of action, and investigate their role in plant-microbe interactions. We also observed that complex interactions between soil chemistry and soil microbial communities limit the direct transferability of results from one soil type to another. Further studies are therefore needed to reliably predict BNI effectiveness across different soils. Overall, the project provides an important scientific foundation for more sustainable agricultural practices. Plant-based nitrification inhibitors have the potential to reduce nitrogen losses, lower greenhouse gas emissions, protect water resources, and allow for a more targeted and environmentally friendly use of synthetic inhibitors. BNIs thus offer promising opportunities for the development of efficient, resource-conserving, and environmentally sustainable fertilization strategies in agriculture.