Discovering the Next Green Revolution
By Annika Peterson
There are more people today living and eating on Earth than ever before. Farmers produce food to feed us through feats of science and innovation. This could not happen without the invention of synthetic nitrogen fertilizers. Crops need key nutrients such as nitrogen, phosphorous and potassium, and of these, nitrogen is often the most scarce in nature. But, the Haber-Borsch process allows us to create bio-available nitrogen synthetically. We no longer only rely on the amount available in nature. This allows farmers to produce enough wheat, corn, and rice to feed the world. In addition to the invention of nitrogen fertilizers, breeding and engineering new varieties of classic crops allows the greatest possible yield. Scientists like Norman Borlaug, called the father of the Green Revolution, improved crops to yield more, and feed more. However, there are drawbacks to this explosive production. The manufacture of nitrogen fertilizers uses non-renewable fossil fuels and their use causes water pollution when excess fertilizer runs off into rivers and the ocean .
Synthetic nitrogen fertilizers have altered the nitrogen cycle: the way nitrogen moves from one form or location to another on the earth. Our atmosphere contains nitrogen, but most organisms cannot use this form. Plants with the ability to fix their own nitrogen can transform it into a usable form. Crops with this ability include soybeans and other legumes. Those without this fixation ability rely on the available nutrients in the soil or those added by fertilizers. Nitrogen fixation takes place with the aid of bacteria called rhizobia. They enter the roots and form nodules; clusters of bacteria surrounded by root. The plant shelters the bacteria, and the bacteria create usable nitrogen . In this symbiotic relationship, the legume and the bacteria both benefit. These plants do not require environmentally taxing nitrogen fertilizers. Unfortunately, grain crops that make up most our food do not have this ability. Cereal crops with the ability to fix nitrogen would reduce environmental impact and increase production potential, especially in parts of the world where fertilizers are prohibitively expensive or not available .
Over the past few decades, scientists have searched for a way to engineer crops to meet the goal of creating nitrogen-fixing cereal crops. Researchers have experimented with various strategies, and some have had success. The breakthroughs and dead ends in this research illustrate a process of scientific development with ups and down, and many discoveries to be made.
Initially, researchers hoped to transform cereals or rhizobia so that they could interact. However, rhizobia are extremely specific to their host plant. Also, they must live anaerobically, without oxygen . In legumes, they live in an oxygen protected cyst which would be hard to reproduce in another type of plant. Despite efforts, this method does not seem to hold much promise . In following decades, researchers continued to investigate methods for creating nitrogen-fixing cereal crops. Through research, we understand the factors that allow for nitrogen-fixing symbiosis. Chemical signaling tells the plant to let down its immune defenses and allows the symbiont to enter . The search for new ideas also includes investigating nitrogen-fixing bacteria not associated with a plant. Since breaking the strong triple bond in atmospheric nitrogen is difficult for free living organisms, most of them partner with plants to accomplish the task. However, cyanobacteria perform photosynthesis and fix their own nitrogen . A free-living nitrogen-fixing organism could potentially associate with cereals. Recently, scientists discovered a bacterium called Glucoacetobacter diazotrophus (Gd) when famers noticed that the levels of nitrogen in their sugarcane fields did not decrease as much as expected after several years of cultivation. Gd is able to colonize both legume and cereals . Investigations with various plants such as Arabidopsis show that it is possible for Gd to colonize a variety of crops, and potentially aid in maintaining levels of available nitrogen in the soil . Gd is the next valuable tool in creating nitrogen-fixing cereal crops. This method has not been refined enough to be used by farmers anytime soon, but it shows great potential for reducing nitrogen fertilizer use and combating climate change !
Nitrogen fixing cereal crops may be the next great revolution in agriculture. But, the scientific process leading researchers’ current understanding has been not been a straightforward path. As with many discoveries, scientists cannot discover a revolutionary new way to grow food overnight. Through more investigation and discovery, many in the field foresee that research will allow agriculture to keep improving to meet our evolving challenges.
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