What is laughing gas commonly known as

Fingerprint for the creation of nitrous oxide emissions

Scientists working with Eliza Harris and Michael Bahn from the Institute for Ecology at the University of Innsbruck have succeeded in examining the emissions of the greenhouse gas nitrous oxide under the influence of environmental factors in an unprecedented level of detail. The study, which has now been published in the journal Science Advances, thus also represents a starting point for the creation of models which could predict future trends in the emission dynamics of greenhouse gases in ecosystems under global climate changes.

Nitrous oxide (N2O), commonly known as laughing gas, is a powerful greenhouse gas whose atmospheric growth rate has accelerated over the past decade. Most of the anthropogenic N2O emissions result from fertilizing the soil with nitrogen, which is converted into N2O through various abiotic and biological processes.

A team of scientists led by Eliza Harris and Michael Bahn from the Functional Ecology research group at the University of Innsbruck has now been able to use these N2O production and consumption paths, which take place within the nitrogen cycle and ultimately lead to the emission of this greenhouse gas, as part of the NitroTrace project funded by the FWF, understand in detail. In a test arrangement in the botanical garden of the University of Innsbruck, 16 intact grassland monoliths from the Kaserstattalm in the Tyrolean Stubai Valley, a location for long-term ecosystem research (LTER), were examined. The soil blocks were exposed to extreme drought and subsequent rewetting. These weather conditions reflect the climatic changes that many regions of the world, including the Alps, are increasingly exposed to. “Our aim was to quantify the net effect of drought and re-humidification on the process of N2O formation and its emissions, which is currently largely unexplored,” says Eliza Harris.

Unexpected result

Contrary to the researchers' expectations, the process of denitrification, i.e. the breakdown of nitrate to N2O and molecular nitrogen (N2) by special microorganisms, dominated even in very dry soils. According to previous assumptions, this process takes place primarily in moist, oxygen-poor soils and through it more N2O is released into the atmosphere. The team had expected that the process of nitrification would predominate in the dry soils, producing nitrate, which is an important chemical compound for plants.

“We assumed that there would be enough oxygen available for nitrification in dry soil. After more detailed investigations, we were able to determine drought-related accumulations of nitrogenous organic matter on the surface of our soil samples and identify them as a trigger for denitrification in dry soil. This indicates a strong role of the so far little researched chemo- and codenitrification pathways, in which additional abiotic and biotic processes lead to the formation of N2O, ”explains Harris the surprising result. Overall, the N2O emission was greatest when rewetting after extreme drought.

The results give researchers an unprecedented insight into the nitrogen cycle and the processes it contains for the formation of the greenhouse gas N2O as a reaction to environmental parameters. A better understanding can help find solutions to reduce greenhouse gas emissions, which have been rising for decades.

New analysis method

The use of laser isotope spectroscopy, which was made possible by the FFG-funded LTER-CWN project, was decisive for the success of the research. “With this new analysis method, we can determine the isotopic composition of N2O. This gives us a kind of fingerprint for the creation process of the emitted N2O, which in turn helps us to understand its microbial creation process, ”says Eliza Harris, emphasizing the importance of this process. With the help of molecular-ecological analyzes, they were also able to determine which microbial genes were involved in nitrogen transformation.

In addition, spatial analysis techniques helped to determine the elementary composition and distribution in the soil. "We hope that by further applying these methods we will gain more knowledge about the feedback effects between climate change and the nitrogen cycle," says Harris. The long-term goal of the researchers is to be able to use models to predict the emission dynamics of ecosystems against the background of climatic changes. (Science Advances, 2021; doi: 10.1126 / sciadv.abb7118).

Source: University of Innsbruck

February 8, 2021

- Kay Sanders