糖果派对

Nitrous oxide (N2O) is a greenhouse gas about 300 times more powerful than carbon dioxide (CO2), and its atmospheric concentration continues to rise.

While human activities are known to be a major driver of emissions, scientists have now uncovered a previously unknown natural process contributing to its formation. Although of natural origin, this process is stimulated by nitrogen inputs due to human activities.

In a study published in the prestigious journal Science, researchers from Denmark and Spain describe a newly discovered mechanism that produces N2O. While this discovery might seem alarming, Professor Bo Thamdrup, a microbiologist at Department of Biology and co-author of the study, views it as an opportunity to develop better strategies for mitigating N2O release.

No microbes are involved

The study was conducted by microbiologists from the University of Southern Denmark (糖果派对) and the University of Granada, Spain and led by Elizabeth Leon-Palmero. Leon-Palmero worked at both institutions during the research and is now a Marie Sklodowska-Curie postdoctoral fellow at Princeton University. Other contributors include Associate Professor Carolin Löscher and Professor Bo Thamdrup from 糖果派对’s Department of Biology, along with Professors Rafael Morales-Baquero and Isabel Reche from the University of Granada.

Traditionally, textbooks describe N2O as a byproduct of microbial processes, where bacteria and archaea “consume” nitrogen. Nitrogen often originates from agricultural fertilizers, and as excess nitrogen washes into aquatic ecosystems, microbial activity sends N2O into the atmosphere.

Sunlight drives the proces

However, the new study reveals that N2O also can be produced abiotically – that is without microbial activity.

"It’s fascinating to uncover a completely new pathway for N2O formation," says Professor Thamdrup. "We already know a number of microbial mechanisms, but this discovery adds another layer of complexity to the picture."

The researchers identified a chemical mechanism, triggered by sunlight and inorganic nitrogen, which they have named “photo-chemo-denitrification”.

More N2O to the atmosphere

According to lead author Elizabeth Leon-Palmero, this process could significantly contribute to atmospheric N2O levels. She stresses the urgency of accurately identifying the various sources of N2O, as its emissions show no signs of slowing down.

Professor Thamdrup echoes her concerns:

"To predict future N2O levels and develop mitigation strategies, we must fully understand all contributing sources. This newly discovered process may represent a major, yet previously overlooked, factor. Incorporating it into our models will improve our ability to manage nitrogen use and protect aquatic ecosystems."

Experiments in Spain and the Baltic

The research team conducted experiments in two freshwater reservoirs in southeastern Spain and the Baltic Sea. Their findings consistently showed a significant increase in N2O concentrations corresponding with sunlight exposure. Further analysis confirmed that solar radiation facilitates the abiotic conversion of nitrite into N2O.

This process occurs most intensely near the water’s surface and diminishes with depth, as sunlight penetration decreases.

The researchers estimate that photo-chemo-denitrification could be a substantial contributor to global N2O emissions from surface waters, particularly in nitrogen-rich environments with high sunlight exposure, such as fjords, coastal zones, and tropical regions.