Another source of global nitrogen: Earth’s bedrock

Sedimentary rocks like sandstone often contain high levels of nitrogen. A photo from the Bryce Canyon National Park in Utah, USA. Photo: Katrin and Tina Speicher

Important connections verified among the atmosphere, the biosphere, and the rocks at Earth’s surface

For centuries, the thinking has been that all the nitrogen available for plant growth worldwide comes from the atmosphere. But a new study by National Science Foundation (NSF)-funded researchers at the University of California (UC) in Davis shows that more than a quarter of that nitrogen is derived from the weathering of Earth’s bedrock. There had been such assumptions before, but now a verification and a quantification has been reached.

The results, published in the journal „Science“, demonstrate that up to 26% of the nitrogen in ecosystems is sourced from rocks, with the remaining amount from the atmosphere.

„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.

Rock-derived nitrogen may fuel the growth of forests and grasslands, and allow them to sequester more carbon dioxide (CO2) than previously thought. Mapping the nutrient profiles in rocks for their carbon uptake potential could help drive conservation efforts, the researchers said.

„Geology might have a huge control over which systems can take up carbon dioxide and which ones can’t,“ said team leader Ben Houlton of UC Davis. „When thinking about carbon sequestration, the geology of the planet can help guide our decisions.“

The work also helps solve the „case of the missing nitrogen“. For decades, scientists have recognized that more nitrogen accumulates in soils and plants than can be explained by input from the atmosphere alone, but researchers couldn’t pinpoint what was missing.

„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.“

In previous work, Houlton and Morford analyzed rocks collected from the Klamath Mountains in northern California, and found that the rocks and the surrounding trees contained large amounts of nitrogen.

In the current study, they built on that work, analyzing the entire planet’s nitrogen balance; the scientists developed a model to assess rock nitrogen availability on a global scale.

Source: National Science Foundation (NSF)

(16.04.2018, USA: 04.16.2018)