UC Davis Researchers Identify A New Source Of Global Nitrogen

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For centuries, scientific community has believed that all of the nitrogen on Earth available to plants comes from the atmosphere. However, scientists at the University of California (UC) Davis in the U.S. have now identified a new source of global nitrogen – the weathering of Earth’s bedrock – which, according to scientists, provides up to 26 percent of the total nitrogen present in the natural ecosystems.

Nitrogen exists naturally in the environment and is constantly converted from organic to an inorganic form and vice versa. The main source of nitrogen include: atmospheric precipitation, livestock, agricultural land, urban waste and poultry operations. The natural cycle of nitrogen involves a variety of biological and non-biological process including: nitrification, denitrification, mineralization, nitrogen fixation, microbial and plant uptake of nitrogen, leaching of nitrite and nitrate, ammonia volatilization, and ammonia fixation.

The new study, published in the journal Science, was funded by National Science Foundation (NSF) and the Andrew W. Mellon Foundation.

“This research reveals important connections among the atmosphere, the biosphere, and the rocks at Earth’s surface,” said Richard Yuretich, a program director in NSF’s Division of Earth Sciences.

“Our study shows that nitrogen weathering is a globally significant source of nutrition to soils and ecosystems worldwide,” said Ben Houlton, a professor at the UC Davis and co-author of the study.

“This runs counter the centuries-long paradigm that has laid the foundation for the environmental sciences,” said Houlton.

“We think that this nitrogen may allow forests and grasslands to sequester more fossil fuel CO2 emissions than previously thought,” he said.

The newly identified nitrogen source may also fuel the growth of forests and grasslands, and allow them to sequester more carbon dioxide than previously thought.

“Geology might have a huge control over which systems can take up carbon dioxide and which ones can’t,” Houlton said.

“When thinking about carbon sequestration, the geology of the planet can help guide our decisions.”

The research has finally solved the “case of the missing nitrogen.” Past studies have revealed that more nitrogen accumulates in plants and soils than can be explained by input from the atmosphere alone. However, they had so far failed to identify the missing link.

“We show that the paradox of nitrogen is literally ‘written in stone,'” said co-author Scott Morford of UC Davis. “There’s enough nitrogen in rocks, and it breaks down fast enough, to explain the cases where there has been this mysterious gap.”

Houlton and Morford had earlier examined the rocks collected from the Klamath Mountains in northern California and observed that these rocks and the surrounding trees contained large amounts of nitrogen. In the current research, they analyzed nitrogen balance of the entire planet. They developed a model to assess the rock nitrogen availability on a global scale.

“These results are going to require rewriting textbooks,” said Kendra McLauchlan, a program director in NSF’s Division of Environmental Biology, which co-funded the research.

“While there were hints that plants could use rock-derived nitrogen, this discovery shatters the paradigm that the ultimate source of nitrogen is the atmosphere. A discovery of this magnitude will open up a new era of research on this essential nutrient.”