ScienceDaily — Nitrogen is vital for all plant life, but increasingly the planet is paying a heavy price for the escalating use of nitrogen fertilizer.

Excess nitrogen from fertilizer runoff into rivers and lakes causes algal blooms that create oxygen-depleted dead zones, such as the 6,000 to 7,000 square mile zone in the Gulf of Mexico, and nitrogen in the form of nitrous oxide is a potent greenhouse gas.

But new findings by Stanford researchers that reveal the inner workings of nitrogen-producing bacteria living inside legumes such as soybeans could enable researchers to blunt those negative effects and aid efforts to make agriculture more sustainable.

“We have discovered a new biological process, by which leguminous plants control behavior of symbiotic bacteria,” said molecular biologist Sharon Long. “These plants have a specialized protein processing system that generates specific protein signals. These were hitherto unknown, but it turns out they are critical to cause nitrogen fixation.”

The ability of legumes to capture nitrogen from the air and turn it into plant food, or “fix” it, also leaves the soil enriched through the plant matter left after harvesting, creating a natural fertilizer for other crops, which is the basis for crop rotation. Alternating legumes with other crops has been a major component of agriculture around the world for thousands of years. Yet until recently, little was known about how nitrogen fixation worked, or why some legumes are efficient at fixing nitrogen and others poor.

The key part of the process that Long’s research group uncovered is a plant gene that triggers a critical chemical signal. Without the signal, no nitrogen gets fixed by the bacteria. Dong Wang, a postdoctoral scholar in Long’s lab who pinned down the gene, is first author of a paper describing the work, published Feb. 26 in Science. Long, a professor of biology, is senior author.

Journal Reference:

1. Dong Wang, Joel Griffitts, Colby Starker, Elena Fedorova, Erik Limpens, Sergey Ivanov, Ton Bisseling, and Sharon Long. A Nodule-Specific Protein Secretory Pathway Required for Nitrogen-Fixing Symbiosis. Science, 2010; 327 (5969): 1126 DOI: 10.1126/science.1184096