If crops could feel envy, it would be for vegetables. 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 is usable by those plants, an essential element for building their tissues, photosynthesizing, and generally staying healthy. This is known as nitrogen fixation. If you look at the roots of a legume, you will see see nodules that provide these nitrogen-fixing microbes with a home and food.
Other crops (cereals like wheat, rice, and corn) don’t have as deep a symbiotic relationship, so farmers have to use large amounts of fertilizer to get the plants the nitrogen they need. This is too 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 really high pressures and temperatures,” says Angela Kent, an Urbana-Champaign plant biologist at the University of Illinois. “Bacteria do this at ambient temperatures and pressures, so they are quite special. While energy has been cheap, it has been easy for us to overuse nitrogenous fertilizers.”
Worse yet, once it’s in the fields, the fertilizer releases nitrous oxide, which is 300 times more powerful a greenhouse gas such as carbon dioxide. Runoff from fields also pollutes water bodies, causing toxic algae blooms. This is a particularly serious problem in the Midwest, where fertilizer flows into the Mississippi River and empties into the Gulf of Mexico, leading to massive blooms each summer. When those algae die, they suck oxygen out of the water, killing any sea creatures unlucky enough to be in the area and creating a notorious aquatic dead zone which can be the size of New Jersey. Climate change is only exacerbating the problem, since warmer waters contain less oxygen to begin with.
Given all that nastiness, scientists have long sought to reduce agriculture’s reliance on fertilizer by giving cereal crops their own nitrogen-fixing power. And with the rise of gene-editing technology in recent decades, that search has been progressing. Last month, in the Plant Biotechnology Journalresearchers described A breakthrough with rice, the engineering of the plant to produce more compounds that encourage the growth of biofilms, which provide a hospitable home for nitrogen-fixing bacteria, just as legumes provide nodules for their associated microbes.
“People for the last 30 or 40 years have been trying to make cereals behave like legumes,” says Eduardo Blumwald, a plant biologist at the University of California, Davis, who co-authored the new paper. “Evolution in that sense is very cruel. You can’t do in the lab what took millions and millions of years.”
So what about evolutionary cruelty? Why do some plants, like, let’s say aquatic tv—fix nitrogen while others cannot?
It is not that other species do not get nitrogen at all, cereal grasses use the nitrogen that is already in the soil: it comes from animal manure, as well as from all the life that stirs on the earth. (Many different bacterial groups process atmospheric nitrogen, not just legume symbionts.)