A Second Nitrogen Revolution?

On a nitrogen-fixing variety of corn, the aerial roots (seen above) secrete sugar-rich gel. The dripping gel harbors bacteria that convert atmospheric nitrogen into a form usable by the plant.

Last fall, the news that ancient corn varieties indigenous to Mexico can fix nitrogen from the air made headlines around the globe. Could we be getting closer to reducing reliance on synthetic fertilizers by helping corn, rice and other non-legumes fix their own N?

A public-private collaboration of researchers at the University of Wisconsin–Madison; the University of California, Davis; and Mars, Inc., has been working for several years to decipher the secrets of the corn, which exudes a mucus-like gel from unusual aerial roots. First identified in the 1980s growing in poor soil on mountain slopes in Oaxaca, “Sierra Mixe” corn can grow up to 16 feet tall and acquire 30 to 80% of its own N from the atmosphere.

It turns out the clear, goopy gel on the multiple sets of aerial roots provides high levels of sugar in a low-oxygen environment, perfect for the resident bacteria that convert atmospheric N into a form that the plant can, and does, use for nutrition. The research team published its work last year, describing DNA sequencing of the bacterial/gel process and its success growing the corn in California and Wisconsin.

The hope is that, in time, modern corn varieties could be bred to produce the brace roots and the gel, or that the gel and its bacteria could be replicated and coated onto the existing brace roots of corn. Both possibilities are likely years away, however.

On a different and possibly more immediate front, several startup companies say they are bringing microbial N-fixing prototype products to market. Millions of dollars continue to be spent on sustainable N research by universities, corporations and groups like the Bill & Melinda Gates Foundation.

There are several reasons for such efforts. The process of making nitrogen fertilizer is extremely energy-intensive and sends harmful greenhouse gases into the air, plus fertilizer is an expensive input for farmers, especially in developing nations, says Manish Raizada, a plant scientist at the University of Guelph, Ontario. His decade-long research includes working with probiotic microbes that can assist plants with organic nitrogen and other nutrients.

Raizada says the Sierra Mixe aerial mucilage is only one approach, and that using endophytes—microorganisms like bacteria and fungi that live in the intercellular spaces of plants—to fix nitrogen is another sustainable solution. “Both avenues need to move forward,” he says. He calls the Mexican corn research “a very promising lead. It’s one of the best leads we’ve ever had.”