New source of global nitrogen discovered

New source of global nitrogen discovered
Nitrogen-rich marine rocks from Northern California. Globally, rocks of sedimentary origin contain on average about 400 parts-per-million nitrogen. Previous assumptions maintained that all nitrogen came from the atmosphere. Credit: Scott Morford/UC Davis

For centuries, the prevailing science has indicated that all of the nitrogen on Earth available to plants comes from the atmosphere. But a study from the University of California, Davis, indicates that more than a quarter comes from Earth's bedrock.

The study, to be published April 6 in the journal Science, found that up to 26 percent of the in natural ecosystems is sourced from rocks, with the remaining fraction from the atmosphere.

Before this study, the input of this nitrogen to the global land system was unknown. The discovery could greatly improve climate change projections, which rely on understanding the cycle. This newly identified source of nitrogen could also feed the carbon cycle on land, allowing ecosystems to pull more emissions out of the atmosphere, the authors said.

"Our study shows that nitrogen is a globally significant source of nutrition to soils and ecosystems worldwide," said co-lead author Ben Houlton, a professor in the UC Davis Department of Land, Air and Water Resources and director of the UC Davis Muir Institute. "This runs counter the centuries-long paradigm that has laid the foundation for the environmental sciences. We think that this nitrogen may allow forests and grasslands to sequester more fossil fuel CO2 emissions than previously thought."

Weathering is key

Ecosystems need nitrogen and other nutrients to absorb pollution, and there is a limited amount of it available from plants and soils. If a large amount of nitrogen comes from rocks, it helps explain how like boreal forests are capable of taking up high levels of carbon dioxide.

New source of global nitrogen discovered
Co-leading author Scott Morford, a UC Davis graduate student at the time of the study, performs field work, which lead to research showing that weathering rocks are a significant source of nitrogen on the planet. Credit: Scott Morford

But not just any can leach nitrogen. Rock nitrogen availability is determined by weathering, which can be physical, such as through tectonic movement, or chemical, such as when minerals react with rainwater.

That's primarily why rock nitrogen weathering varies across regions and landscapes. The study said that large areas of Africa are devoid of nitrogen-rich bedrock while northern latitudes have some of the highest levels of rock nitrogen weathering. Mountainous regions like the Himalayas and Andes are estimated to be significant sources of rock nitrogen weathering, similar to those regions' importance to global weathering rates and climate. Grasslands, tundra, deserts and woodlands also experience sizable rates of rock nitrogen weathering.

Geology and carbon sequestration

Mapping nutrient profiles in rocks to their potential for carbon uptake could help drive conservation considerations. Areas with higher levels of rock nitrogen weathering may be able to sequester more carbon.

"Geology might have a huge control over which systems can take up carbon dioxide and which ones don't," Houlton said. "When thinking about , the geology of the planet can help guide our decisions about what we're conserving."

New source of global nitrogen discovered
The Pinnacles of Gunung Mulu in Borneo are an example of where limestone rock weathering would be expected to produce significant levels of nitrogen. Credit: Paul White on Flickr (Creative Commons)

Mysterious gap

The work also elucidates the "case of the missing nitrogen." For decades, scientists have recognized that more nitrogen accumulates in soils and plants than can be explained by the atmosphere alone, but they could not pinpoint what was missing.

"We show that the paradox of nitrogen is written in stone," said co-leading author Scott Morford, a UC Davis graduate student at the time of the study. "There's enough nitrogen in the rocks, and it breaks down fast enough to explain the cases where there has been this mysterious gap."

In previous work, the research team analyzed samples of ancient rock collected from the Klamath Mountains of Northern California to find that the rocks and surrounding trees there held large amounts of nitrogen. With the current study, the authors built on that work, analyzing the planet's , geochemical proxies and building a spatial nitrogen weathering model to assess rock nitrogen availability on a global scale.

The researchers say the work does not hold immediate implications for farmers and gardeners, who greatly rely on nitrogen in natural and synthetic forms to grow food. Past work has indicated that some background nitrate in groundwater can be traced back to rock sources, but further research is needed to better understand how much.

Rewriting textbooks

"These results are going to require rewriting the textbooks," said Kendra McLauchlan, program director in the National Science Foundation'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 available nitrogen is the atmosphere. Nitrogen is both the most important limiting nutrient on Earth and a dangerous pollutant, so it is important to understand the natural controls on its supply and demand. Humanity currently depends on to produce enough fertilizer to maintain world food supply. A discovery of this magnitude will open up a new era of research on this essential nutrient."

Explore further

Team discovers a significant role for nitrate in the Arctic landscape

More information: B.Z. Houlton el al., "Convergent evidence for widespread rock nitrogen sources in Earth's surface environment," Science (2018). … 1126/science.aan4399
Journal information: Science

Provided by UC Davis
Citation: New source of global nitrogen discovered (2018, April 5) retrieved 15 October 2019 from
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User comments

Apr 05, 2018
I wonder when some yahoo is going to come here and claim that since scientists are discovering this now, this proves that scientists know nothing and therefore climate change is a hoax. Hopefully the denialists have been sufficiently burned by posting anti-science on a science website they won't bother.

Apr 06, 2018
P, wait for it...
Once they are paid? The denier agitprop will be all over these comments. Like swarming bedbugs.

Apr 06, 2018
I'm going with "swarming cockroaches."

Meanwhile, this is a pretty significant discovery with implications far beyond climate modeling and global climate change. They're right, a lot of textbooks are going to require new editions at minimum.

Apr 07, 2018
Fakers that promulgate the sick anti-science Malthusian worldview are perhaps themselves a prominent source of nitrogen. For it is apparent that they must have rocks in their heads.

Apr 07, 2018
Crazy what we're still discovering. Also kinda scary trying to imagine how backward our thinking might be in so many areas despite it possibly being accepted as prevailing science.

Apr 07, 2018
Vic D, in general I agree with your comments. However, we know what we know and that's the best any of us can do. Past, Present or Future.

Each generation of researchers, innovators, inventors and creators builds upon those who came before.

Unfortunately, swindlers, frauds, quacks, cultists and deniers use previous errors to excuse their attacks on the Scientific Method.

We are all fallible, we all make mistakes. The best protection is a strong skepticism of all claims. Especially those that claim definitive conclusions. All Science is open to new examination of methods and data. New technology redefines and corrects previous work.

We can recognize crank pseudo-science by their inability to repeat their experiment. To confirm if the results match their predictions. That's where the cranks fall apart. When their claims do not match reality.

Speculation is fun. Then comes the hard part of verifying if your idea is valid.

Apr 07, 2018
carbon dioxide pollution

CO2 isn't pollution, but this narrative help provide a fictional basis for government control of the means of production.

Plant trees. Paint artificial sky facing surfaces, white. Problem, if there really ever was a problem, resolved.

Apr 10, 2018
They don't even know where the origin of much of the nitrogen, yet they claim to know where all the C02 comes from.

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