The yield and quality of soybeans can be increased dramatically by using a method developed by Mechthild Tegeder, a Washington State University biologist. Her soybean plants, grown in a greenhouse, produce up to 36 percent more seeds, fix double the amount of nitrogen gas from the atmosphere and grow larger than their natural counterparts.
Tegeder and Amanda Carter, a biological sciences graduate student designed an innovative way to increase the flow of nitrogen from specific bacteria in soybean root nodules to the seed-producing organs. Nitrogen is an essential nutrient and the increased rate of supply jolted the plants into overdrive.
This work could ultimately help address society’s critical challenge of feeding a growing human population while protecting the environment. It is viewed as a key advance in the science of improving crop yields.
Legumes consist of plants like beans, peas, soybeans, alfalfa, and lentils. These account for about 30 percent of the world’s agricultural production. Legumes contain rhizobia bacterioids in their root nodules. These bacteria have the unique capability of transforming or “fixing” nitrogen gas from the atmosphere, unlike crops that rely on naturally occurring or artificially made nitrogen from the soil.
Tegeder feels that the biggest implication of their research is that the amount of food that can be produced is increased by boosting the natural nitrogen allocation process, without contributing to further agricultural pollution. She eventually aims to transfer what they have learned to other legumes and crops that humans grow.
Scientists have in the past tried to increase the rate of nitrogen fixation in legumes by altering the interactions that take place between the bacterioid and the root nodule cells, or by changing rhizobia bacterioid’s function.
Tegeder approached the problem differently by increasing the number of proteins that help move nitrogen from the rhizobia bacteria to the plant’s seed-producing organs, leaves and other areas where it is needed.
This increased the speed with which nitrogen is exported from the root nodules. A feedback loop was initiated and this caused the rhizobia to start fixing more nitrogen gas from the atmosphere. The plant then used this to produce more seeds.
Tegeder notes that the modified plants grow faster, are bigger and generally look better than natural soybean plants. There is also some evidence that they might be highly efficient under stressful conditions like drought.
Insufficient plant nitrogen results in low crop yields and limited food supplies in developing countries where nitrogen fertilizer is scarce.
As nitrogen is a macronutrient essential for plant growth, big amounts of synthetic nitrogen fertilizer is applied internationally to ensure high plant productivity. This application causes environmental issues such as increased greenhouse gas emissions, high energy input requirements, water pollution and other adverse effects on human health and ecosystems in industrialized countries like the United States.
One major benefit of growing legumes such as common beans, chickpeas, peas and soybeans is that they not only leave lasting nitrogen in the soil for subsequent crops, but can also use atmospheric nitrogen gas for their own growth. Tegeder believes her research, although currently focused on soybeans, can eventually be applied to a variety of legumes suited to a diverse array of climates.
Increased nitrogen fixation could diminish or eliminate the need for nitrogen fertilizers while improving overall plant productivity for farmers who grow legumes in both developing and industrial countries.
Tegeder adds that legumes with higher yields have huge implications for agriculture and food production around the world. This new research has the potential to be transferred to other crop plants – not only those that fix nitrogen from the atmosphere, but crops taking nitrogen directly from the soil would benefit from a more efficient uptake.
The full study was published in the journal Current Biology.