Posted in | Global Warming

Biological Mechanism Converts Nitrogen to Ozone-Depleting Greenhouse Gas

A team of researchers from Cornell have developed a biological mechanism that facilitates conversion of nitrogen-based fertilizer into nitrous oxide, an ozone-depleting greenhouse gas. The research findings were published online in the Proceedings of the National Academy of Sciences (on November 17).

Jonathan Caranto, left, Kyle Lancaster, assistant professor of chemistry and chemical biology, and Avery Vilbert examine a thin vial of cytochrome P460 that helps to convert agricultural nitrogen (fertilizer) into nitrous oxide, an ozone-depleting greenhouse gas. (credit: Blaine Friedlander/Cornell Chronicle)

The first key to plugging a leak is finding the leak. We now know the key to the leak and what’s leading to it. Nitrous oxide is becoming quite significant in the atmosphere, as there has been a 120 percent increase of nitrous oxide in our atmosphere since pre-industrial times.

Kyle Lancaster, assistant professor of chemistry and chemical biology, and senior author on the research

Lancaster, along with postdoctoral researcher Jonathan D. Caranto and chemistry doctoral candidate Avery C. Vilbert, demonstrated that an enzyme created by the ammonia oxidizing bacterium Nitrosomonas europaea, cytochrome P460, produces nitrous oxide after the organism converts ammonia into an intermediate metabolite known as hydroxylamine.

Hydroxylamine is used as fuel source by N. europaea and similar “ammonia-oxidizing bacteria”, and the resulting production of nitrous oxide is a chemical coping strategy. However, too much hydroxylamine can be harmful.

Lancaster and his colleagues theorize that when ammonia-oxidizing bacteria are exposed to large quantities of nitrogen compounds, such as in wastewater treatment plants or crop fields, then nitrous oxide production via cytochrome P460 will increase.

In the atmosphere, greenhouse gases are a concoction of several species, and Lancaster explained that nitrous oxide possesses 300 times the potency of carbon dioxide. “That’s a staggering number,” he said. “Nitrous oxide is a really nasty agent to be releasing on a global scale.”

Lancaster further explained that nitrous oxide is photochemically reactive and can form free radicals – ozone-depleting agents – which worsen the problem of blanketing Earth’s atmosphere with more gas and increasing the global temperature. “In addition to its role as a greenhouse gas cloak, it’s removing our protective shield,” Lancaster said.

According to the U.S. Department of Agriculture’s Economic Research Service, the U.S is one of global importers of nitrogen fertilizer. The Food and Agriculture Organization of the United Nations stated that the nitrogen fertilizer global demand was estimated to be 116 million tons for this recent agricultural season.

“For the world, I realize that we are trying to feed more people and that means more fertilizer – and that means more nitrous oxide,” said Lancaster, who noted that roughly 30 % of nitrous oxide emissions are caused by the agriculture sector and its related land use. Already farmers are using nitrification inhibitors to decrease the nitrogen’s negative impact.

Said Lancaster: “While it will be challenging to develop ways to stop this process, now we have pinpointed one biochemical step leading to nitrous oxide production. Future work may lead to inhibitors, molecules that can deactivate or neutralize this bacterial enzyme. Alternatively, we may just use this new information to develop better strategies for nitrogen management.”

The research was supported by the Department of Energy Office of Science and the National Institutes of Health.

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