Bacteria Offers Promise to Curb N2O Emissions from Farms

A recent study published in Nature proposes that soil bacteria can reduce the greenhouse gas emissions produced by food production. This research was conducted by the Norwegian University of Life Sciences (NMBU) and IIASA.

Nitrogen fertilization leads to nitrous oxide (N₂O) emissions from agricultural soils, which comprise a significant amount of total greenhouse gas emissions from agriculture. It has long been believed that N₂O emissions are unavoidable. 

However, an international team of researchers led by the NMBU has developed a way to minimize these emissions. They discovered bacteria that can “consume” nitrous oxide as it grows in soil, preventing it from escaping into the atmosphere. The researchers predict that using this approach alone might cut agricultural nitrous oxide emissions in Europe by one-third.

The N_₂O Problem

Plants require a lot of nitrogen to flourish. A thriving agriculture, therefore, needs an abundance of nitrogenous fertilizer. This was a barrier in agriculture until Fritz Haber developed a method for producing nitrogen fertilizer from atmospheric nitrogen. For the past 120 years, this technology has helped the world's food supply keep up with population increase.

Fertilization increases the generation of the greenhouse gas N_₂O by microorganisms in the soil.

This greenhouse gas has an effect that is about 300 times stronger than CO_₂, and agriculture accounts for about three-quarters of Europe’s N₂O emissions...Also, globally, agriculture is the primary source of nitrous oxide in the atmosphere. Nitrous oxide emissions are primarily regulated by soil bacteria, making reduction efforts challenging due to their elusive nature.

Wilfried Winiwarter, Study Co-Author and Senior Researcher, International Institute for Applied Systems Analysis

Bacteria Can Do the Job

For more than two decades, scientists at NMBU have investigated how soil microbes transform nitrogen. They have extensively analyzed bacteria in hypoxic environments—that is, environments in which bacteria have insufficient oxygen.

Certain areas of the soil become hypoxic following fertilization and rainfall. The bacteria are compelled to find alternative energy sources as they are deprived of oxygen. Numerous microorganisms can use nitrate in place of oxygen and transform it into other gases through a process known as denitrification. In this way, the microorganisms contribute to greenhouse gas emissions, one of which is nitrous oxide.

The researchers have created a novel approach to studying denitrification and have made important discoveries about managing this process. They employ robotic solutions in the field and in the lab and have also created a unique robot capable of measuring soil nitrous oxide emissions in real time.

By using a specific type of bacteria that is incapable of producing nitrous oxide, but can convert it into nitrogen gas (N_₂), which is safe, it is possible to lower emissions of N₂O.

Reducing N₂O emissions involves using a particular kind of bacteria that can convert nitrous oxide to innocuous nitrogen gas (N_₂) but cannot create nitrous oxide itself.

If we grow these microbes in organic waste used as fertilizer, we can reduce N_₂O emissions. This could mean a solution to the problem of N_₂O emissions from agriculture, but it was not easy to find the right bacterium. It must be able to grow quickly in organic waste, function well in soil, and live long enough to reduce N_₂O emissions through an entire growing season. It was also a challenge to go from testing this in the laboratory to trying it out in nature and to ensure that it actually reduced N_₂O emissions in the field.

Lars Bakken, Study Lead Author and Professor, Norwegian University of Life Sciences

The study team is working to identify other bacteria that consume nitrous oxide. They plan to test them in various forms of organic waste used as fertilizer worldwide. The objective is to identify various bacteria capable of functioning in various soil types and fertilizer mixes.

Journal Reference:

‌Hiis, E. G., et al. (2024) Unlocking bacterial potential to reduce farmland N₂O emissions. Nature. doi:10.1038/s41586-024-07464-3