Washington State University biologists have developed a way to dramatically increase the yield and quality of soybeans—producing plants that convert twice as much nitrogen from the atmosphere as their natural counterparts, grow larger and generate up to 36% more seeds.

Mechthild Tegeder, professor of plant molecular physiology, designed a method to increase the flow of nitrogen, an essential nutrient, from specialized bacteria in soybean root nodules to the seed-producing organs. She and graduate student Amanda Carter found that the increased rate of nitrogen transport boosted the plants' growth significantly.

Tegeder's soybean plants grow larger and generate up to 36% more seeds than their natural counterparts. Image credit: WSU.Tegeder's soybean plants grow larger and generate up to 36% more seeds than their natural counterparts. Image credit: WSU.“The biggest implication of our research is that by ramping up the natural nitrogen allocation process, we can increase the amount of food we produce without contributing to further agricultural pollution,” Tegeder says. “Eventually, we would like to transfer what we have learned to other legumes and plants that humans grow for food.”

Legumes account for around 30% of the world’s agricultural production and include plants such as soybeans, alfalfa, peas, beans and lentils. Unlike crops that rely on naturally occurring and artificially made nitrogen from the soil, legumes contain rhizobia bacterioids in their root nodules that have the unique capability of converting nitrogen gas from the atmosphere.

For years, scientists have tried to increase the rate of nitrogen conversion in legumes by altering rhizobia bacterioid function or interactions that take place between the bacterioid and the root nodule cells.

Tegeder took a different approach, increasing the number of proteins that help move nitrogen from the rhizobia bacteria to the plant’s leaves, seed-producing organs and other areas where it is needed. The additional transport proteins sped up the overall export of nitrogen from the root nodules, initiating a feedback loop that caused the rhizobia to start converting more atmospheric nitrogen, which the plant then used to produce more seeds.

Nitrogen is a macronutrient essential for plant growth, and large amounts of synthetic nitrogen fertilizer are applied around the world to ensure high plant productivity. However, application is an environmental issue in industrialized countries like the United States because of high energy input, greenhouse gas emissions, water pollution and other adverse effects on ecosystems and human health. In developing countries, where nitrogen fertilizer is scarce, insufficient plant nitrogen results in low crop yields and limited food supplies.

Tegeder believes her soybean-focused research can eventually be applied to varieties of legumes suited to a diverse array of climates. A major benefit of growing legumes such as chickpeas, common beans, peas and soybeans is that they not only can use atmospheric nitrogen for their own growth, but also leave residual nitrogen in the soil for subsequent crops.

Hence, increasing nitrogen conversion could improve overall plant productivity for farmers who grow legumes, while diminishing or eliminating the need for nitrogen fertilizers.

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