[permaculture] New source of global nitrogen discovered | EurekAlert! Science News ||| rock - remineralize the Earth - rockdust

Lawrence London lfljvenaura at gmail.com
Fri Apr 6 00:46:13 EDT 2018

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New source of global nitrogen discovered | EurekAlert! Science News

New source of global nitrogen discovered

Rocks could hold key to carbon storage and improved global climate

University of California - 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 nitrogen 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 carbon 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 weathering 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


Ecosystems need nitrogen and other nutrients to absorb carbon dioxide
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
natural ecosystems like boreal forests are capable of taking up high levels
of carbon dioxide.

But not just any rock 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.


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 carbon
sequestration, the geology of the planet can help guide our decisions about
what we're conserving."


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
nitrogen balance, 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.


"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
atmospheric nitrogen 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."


UC Davis Professor Randy Dahlgren in the Department of Land, Air and Water
Resources co-authored the study.

The study was funded by the National Science Foundation's Division of Earth
Sciences and its Division of Environmental Biology, as well as the Andrew
W. Mellon Foundation.

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