The Indigenous Mexican Corn That Uses Air as Fertilizer - The Atlantic

Science <https://www.theatlantic.com/science/>
The Wonder Plant That Could Slash Fertilizer Use
An indigenous Mexican corn gets its nitrogen from the air. Ed Yong
<https://www.theatlantic.com/author/ed-yong/> Aug 9, 2018
https://www.theatlantic.com/science/archive/2018/08/amaizeballs/567140/

For thousands of years, people from Sierra Mixe, a mountainous region in
southern Mexico, have been cultivating an unusual variety of giant corn.
They grow the crop on soils that are poor in nitrogen—an essential
nutrient—and they barely use any additional fertilizer. And yet, their corn
towers over conventional varieties, reaching heights of more than 16 feet.

A team of researchers led by Alan Bennett
<https://biology.ucdavis.edu/people/alan-bennett> from UC Davis has shown
that the secret of the corn’s success
<http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2006352>
lies in its aerial roots—necklaces of finger-sized, rhubarb-red tubes that
encircle the stem. These roots drip with a thick, clear, glistening mucus
that’s loaded with bacteria. Thanks to these microbes, the corn can
fertilize *itself* by pulling nitrogen directly from the surrounding air.

The Sierra Mixe corn takes eight months to mature—too long to make it
commercially useful. But if its remarkable ability could be bred into
conventional corn, which matures in just three months, it would be an
agricultural game changer.

All plants depend on nitrogen to grow, and while there’s plenty of the
element in the air around us, it’s too inert to be of use. But bacteria can
convert this atmospheric nitrogen into more usable forms such as ammonia—a
process known as fixation. Legumes, like beans and peas, house these
nitrogen-fixing bacteria in their roots. But cereals, like corn and rice,
largely don’t. That’s why American farmers need to apply more than 6.6
million tons of nitrogen to their corn crops every year, in the form of
chemical sprays and manure.

“All that fertilizer takes a lot of energy to produce, and the excess ends
up in places where it distorts the nutrient balance, creating algae blooms
and dead zones
<https://www.theatlantic.com/science/archive/2018/01/suffocating-oceans/550415/>
in waterways,” says Jeremy Yoder <https://jbyoder.org/>, an evolutionary
biologist at California State University, Northridge who was not involved
in the study. “So self-fertilizing [corn] could substantially cut the cost
and environmental impact of a staple crop.” It could also make it easier to
grow the crop in developing countries where fertilizer is unaffordable or
in areas where soils are poorer.

Crucially, the Davis team involved the Sierra Mixe community throughout
their research. They also established legal agreements with the Mexican
government
<https://www.gob.mx/semarnat/prensa/variedad-de-maiz-nativo-mexicano-captura-nitrogeno-con-lo-que-se-evitarian-fertilizantes-quimicos>
to ensure that any benefits from their research—and its subsequent
commercialization—would be shared with the community, under the auspices of
the Nagoya Protocol
<https://www.salford.ac.uk/__data/assets/pdf_file/0009/956826/Paper_AEC1607_Nagoya-Protocol.pdf>,
an international framework intended to thwart bio-piracy. Alejandra
Barrios, the director of biosafety and biodiversity at Mexico’s
environmental agency <https://www.gob.mx/semarnat>, repeatedly praised the
approach on Twitter
<https://twitter.com/alematraz/status/1027017796419497984>, calling it
“great work” and a “win-win solution.”

The certificate that ratifies the agreement is the first of its kind to be
“issued by the Mexican government, and the first issued to any entity in
the U.S. by any country,” says Howard-Yana Shapiro, an agricultural
scientist from Mars, Incorporated who initiated the project. “That is as
important as the discovery. We’re showing the way of the future.”

Corn, or maize, originated in southern Mexico when it was domesticated from
a wild cereal called teosinte. The region is still home to the greatest
diversity of the crop, with thousands of unique varieties or “landraces.”
In 1980, Shapiro (who was then an independent researcher) was busily
collecting these landraces on behalf of the Mexican government when he
heard about the giant, mucus-covered corn.

From the start, he suspected that the plant might fix its own nitrogen, and
that the shining mucus was somehow involved. But with the technology of the
time, he had no way of testing his hunch. And without that evidence, other
scientists were rightfully skeptical, including the team at Davis. “I would
talk about this maize, and Alan would say, ‘It’s not possible,’” Shapiro
recalls. “I said it *is* possible but I just don’t know how to prove it.
And I took him to Sierra Mixe for a visit in 2008. He was gobsmacked. He
said, ‘I take it all back. There’s something going on here.’”

To find out what was really happening, the team used modern DNA-sequencing
techniques to show that the mucus contains microbes that belong to
nitrogen-fixing families, and that carry nitrogen-fixing genes. They also
chemically analyzed the mucus to show that it provides its resident
microbes with exactly the conditions they need to thrive—an all-you-can-eat
buffet of sugar, and protection from oxygen.

Next, they used five different tests to confirm that the microbes really
are fixing nitrogen, that the nitrogen moves into the corn, and that the
corn gets a *lot *of its nitrogen—anywhere from 30 to 80 percent—in this
way. All five techniques have their own shortcomings, but together “they
all pointed to the same conclusion,” Bennett says. “We’ve been working on
this for 10 years and we have a high degree of confidence that the results
we report are correct.”

Others agree: “It was a very ambitious study that was really well done, and
the results should be believed,” says Michael Kantar
<http://manoa.hawaii.edu/ctahr/tpss/faculty-staff>, a botanist at the
University of Hawai’i at Mānoa. Yoder points out that the team hasn’t
identified the specific nitrogen-fixing microbes, but beyond that, “I think
it’s pretty convincing,” he told me. “Aerial-root mucilage that hosts
nitrogen-fixing microbes is, quite honestly, a thing I’d have called a
little far-fetched if I saw it on an episode of Star Trek,” he added on
Twitter <https://twitter.com/JBYoder/status/1026994900611424257>.

Scientists have spent years trying to create nitrogen-fixing cereal crops
through genetic engineering
<https://www.sciencedirect.com/science/article/pii/S1369526610001056?via%3Dihub>,
with little progress to show for it. But since we now know that at least
one type of corn can fix nitrogen naturally, the ability could potentially
be moved into conventional varieties through classical crossbreeding, mucus
transplants, or both. These methods might make the final produce more
publicly acceptable than a genetically edited crop.

For now, Bennett and his colleagues want to identify the genes that allow
the Sierra Mixe corn to produce its mucus-coated aerial roots, and attract
the right bacteria. They also want to take a closer look at the microbes
themselves. “We’ve isolated thousands, but of those, we don’t know if there
are two species that are really important or a hundred,” Bennett says.

And Shapiro, with the blessing of the Sierra Mixe community, is trying to
find a company to take charge of commercialization. “It probably won’t be
Mars Inc., ’cause we’re not a maize company,” he says, “but I’m trying to
find the right partner.”

Kantar cautions that it’s too early to say if there are any big
implications for food security, because the team hasn’t shown that the
resulting corn can fix enough nitrogen to grow at commercially useful
scales. It’s also unclear if the genes behind the ability come with any
drawbacks. But “if these questions can be resolved, this may provide a way
to significantly reduce fertilizer use worldwide, which would have hugely
beneficial environmental effects,” he says.

Kristin Mercer from Ohio State University is similarly cautious.  ‘This
corn has been likely doing a very good job ensuring some level of food
security for families in the region for a long time,” she says. “If one
were to think about capturing that beneficial diversity and distributing it
more widely, a number of potential issues arise
<https://mercerlab.cfaes.ohio-state.edu/sites/hcs.mercerlab/files/imce/publications/Mercer-Perales-and-Wainwright-2012-Climate-change-and-TAS-smallholder-livelihoods-climate-justice-and-maize-landraces-in-Mexico.pdf>.”
Are there intellectual property issues around dispersing the genetic
variation underlying this trait into public or private breeding programs?
Would it be a good approach to create varieties of nitrogen-fixing corn for
other areas where poor farmers live and asking them to buy those varieties?

“It is easy to jump from describing the amazing biology of these genetic
resources stewarded by farmers in the region for millennia to trying to
solve the world’s massive, intractable problems—but that is stickier than
it may seem,” Mercer adds.
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