Exploring how microbes in permafrost contribute to nitrous oxide emissions

Ecologist Christina Biasi is exploring the conditions under which tiny organisms contribute to permafrost soils emitting nitrous oxide. Her research could be essential for the development of future climate scenarios.

More than 15 years ago, Biasi and her colleagues from the University of Eastern Finland made a surprising discovery. These ecologists measured gas flows from permafrost soils in the Arctic tundra—i.e. soils that are continuously frozen for a period of more than two years. Usually, these soils emit carbon dioxide (CO₂) and methane (CH₄).

“When analyzing samples in the gas chromatograph, we were amazed to also find high concentrations of nitrous oxide (N₂O). We had to dilute the samples in order to be able to measure them. That was absolutely unexpected,” says Biasi, who is now conducting research at the University of Innsbruck.

In 2009, she published her findings in one of the first research papers on N₂O emissions from permafrost soils.

In her current research project “Constraining the global permafrost nitrous oxide budget” (PERNO), Biasi wants to find out how N₂O, also known as laughing gas, is produced in these soils. Knowing this could help to make statements about the future. She suspects that previously disregarded emissions are accelerating global warming even further.

Frozen ground and tiny creatures

“N₂O is linked to the nitrogen cycle. The main sources are agricultural surfaces that are treated with nitrogen-based fertilizers,” explains Biasi. As a matter of fact, the greenhouse gas is also emitted by natural ecosystems. Permafrost soils, however, were long considered to be negligible sources. It was assumed that they were nitrogen-limited.

“Meanwhile, we know that this is not always the case and that nitrous oxide is outgassed at very high rates from special permafrost locations as found in the Arctic or tundra,” notes Biasi. In addition, the consequences of the climate crisis are changing the dynamics in these frozen soils.

Microscopic creatures are involved in the nitrogen cycle in soils. Certain types of microbes obtain energy by reducing ammonia or ammonium to nitrate. Others convert nitrate mainly to nitrogen (N₂), but also to nitrous oxide under low-oxygen conditions. When permafrost soils thaw, the microbes find more organic material they can convert. As a result, nitrogen and nitrous oxide can also be outgassed from these soils.

Small-scale climate models

“We want to decipher this nitrogen cycle in different scenarios,” says Biasi. Together with Ph.D. student Matej Znaminko and research assistant Tatiana Trubnikova, Biasi is analyzing samples from about 50 peat bog soils. The samples come from different regions of the world—including Canada, Siberia and Scandinavia—as well as from different soil depths.

The researchers received many soil samples from international cooperation partners, such as colleagues from the University of Eastern Finland. In the laboratory, they exposed the soil to temperatures of 4°C, 12°C and 20°C, and they also varied the humidity levels.

“In this way, we want to find out how N₂O emissions change when temperatures rise as a result of the climate crisis and the water balance changes, for instance as a result of droughts,” explains Biasi. The team will then analyze which greenhouse gases are emitted at what concentration levels.

The researchers want to understand which microbes in which scenarios contribute to soils emitting more N₂O. This will be done by isotope analysis, a method that is based on two facts: slightly less than 1% of the nitrogen that occurs in nature has more neutrons than protons in its nucleus. These so-called nitrogen-15 atoms have a higher mass than the more common nitrogen-14 atoms.

And secondly, microorganisms prefer nitrogen-14 atoms. “Through isotope analysis, we see a fingerprint of N₂O that shows us which microbial processes are active in the processing of nitrogen,” explains Christina Biasi.

It’s the impact that counts

There is room for new findings in permafrost research. “We have already found unknown types of microorganisms in our samples that cause N₂O emissions. They belong to the group of archaea,” says Biasi. She now wants to find out how these single-cell organisms behave when it gets drier, perhaps also more humid and warmer—and what this means for the global climate.

Nitrous oxide accounts for 5% of man-made greenhouse gas emissions. While carbon dioxide and methane (CH₄) are the most relevant greenhouse gases worldwide because of their quantities, nitrous oxide has a warming potential 300 times higher than CO₂. What’s more, N₂O emissions have risen by 40% since the 1980s.

Dry soils, high emissions

Biasi and her team set out to simulate developments of N₂O in the permafrost regions of the Arctic and the tundra. “The database is ready. The model has been run with the raw values, and the experiments that provide the data to adapt and refine the model are currently in progress,” says the ecologist.

The final results will be communicated at the end of the project in August 2025. Based on the current state of knowledge, Biasi can already say “It is assumed that nitrous oxide emissions in Arctic regions will increase.” Global warming could be fueled further by that.

“How these emissions develop,” Biasi notes, “depends above all on how warm it will get. It is currently assumed that around 80% of the permafrost in the northern peat bogs will be lost by 2100.” This not only means higher N₂O emissions. When permafrost peat soils thaw, microbes break down organic material consisting of carbon, a process that releases enormous amounts of CO₂.

A nation nobody wants

According to Biasi, the time to act to limit global warming is now. If we do too little, the thawing of permafrost soils will accelerate global warming enormously. By 2100, the global permafrost soils, thawing or fully thawed, could emit as many CO₂ equivalents as nations that are among the largest emitters—such as China or the U.S..

“In that case, we can actually call it a permafrost nation of its own. This is an irreversible development. Once permafrost has thawed, it doesn’t form again anytime soon,” says Biasi.

N₂O emissions from permafrost soils have long been excluded from forecasts, including the reports by the Intergovernmental Panel on Climate Change (IPCC). They were only included in the most recent synthesis report from 2023.

With her research, Biasi wants to help predict and include these little-noticed emissions—to heighten understanding of our warming world.