The Long, Leguminous Quest to Give Crops Nitrogen Superpowers

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If crops could to feel envy, it would be for the legumes. Bean plants have a superpower. Or more accurately, they share one. They have developed symbiotic relationships with bacteria that process atmospheric nitrogen into a form that can be used by these plants, an essential element for building their tissues, photosynthesising and generally staying healthy. This is known as nitrogen fixation. If you look at the roots of a legume, you will see nodules that provide these nitrogen-fixing microbes with a home and food.

Other crops (cereals such as wheat, rice, and corn) do not have such a deep symbiotic relationship, so farmers must use large amounts of fertilizer to get plants the nitrogen they need. This is very expensive. And the production of fertilizers is not good for the environment. It is not easy to convert atmospheric nitrogen into a form of nitrogen that plants can absorb on their own. “It takes a lot of energy and very high pressures and high temperatures,” says Angela Kent, a plant biologist at the University of Illinois at Urbana-Champaign. “Bacteria do this at ambient temperatures and pressures, so they’re pretty special. Even though energy has been cheap, it’s been easy for us to overuse nitrogen fertilizers.”

Even worse, once in the fields, the fertilizer emits nitrous oxide, which is 300 times more potent a greenhouse gas than carbon dioxide. Runoff from fields also pollutes water bodies, leading to toxic algal blooms. This is a particularly bad problem in the Midwest, where fertilizers flow into the Mississippi River and flow into the Gulf of Mexico, fueling massive blooms each summer. When these algae die, they suck the oxygen out of the water, killing any sea creatures unlucky enough to be in the area and creating a notorious aquatic dead zone that can be as large as New Jersey. Climate change is only exacerbating the problem, as warmer waters contain less oxygen to begin with.

Given all this nastiness, scientists have long tried to reduce agriculture’s reliance on fertilizers by giving grain crops their own nitrogen-fixing powers. And with the rise of gene-editing technology over the past few decades, this research has been moving forward. Last month, in Journal of Plant BiotechnologyThe researchers described a breakthrough with rice, engineering the plant to produce more compounds that encourage the growth of biofilms, which provide a cozy home for nitrogen-fixing bacteria, just as legumes provide nodules for their microbes. partners.

“People for the last 30 to 40 years have been trying to make grains behave like legumes,” says Eduardo Blumwald, a plant biologist at the University of California, Davis, who co-authored the new paper. “The evolution in this sense is very cruel. You can’t do in the lab what took millions and millions of years.”

So what about evolutionary cruelty? Why can some plants, such as water ferns, fix nitrogen while others cannot?

It’s not that the other species don’t get any nitrogen. Cereal grasses use nitrogen that is already in the soil: it comes from animal manure, as well as all the life that stirs in the dirt. (Many different groups of bacteria process atmospheric nitrogen, not just legume symbionts.)

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