Rocks, the New Source of Nitrogen

Nitrogen is a naturally occurring element that is essential in most of the compounds that allow life to exist. Plants use it to grow and humans use it in many things like fertilizers, steel manufacturing, cooling and to refine oil. A new study found what might be a new source of nitrogen.

Almost 78 percent of the earth’s atmosphere is nitrogen. The commonly known nitrogen cycle would happen when “Nitrogen-fixing microorganisms capture atmospheric nitrogen by converting it to ammonia, which can be taken up by plants and used to make organic molecules. The nitrogen-containing molecules are passed to animals when the plants are eaten. They may be incorporated into the animal’s body or broken down and excreted as waste.” Bacteria convert the waste nitrogen back to nitrogen gas, which returns to the atmosphere.

Benjamin Houlton, a biogeochemist professor at the University of California, Davis, says that plants currently absorb about 30% of human carbon dioxide emissions. Their ability to do this is limited by how much nitrogen they have access to because they need the nutrient to make biomolecules.

For many years scientists recognized that more nitrogen accumulated in the soil and plants which couldn’t be explained by nitrogen absorption from the atmosphere; scientists couldn’t pinpoint what was missing.

A new study found that up to 26 percent of nitrogen comes from rocks! researchers claim that about 15 tera­grams of nitrogen produced by rock weathering. “Through tectonic upheaval, physical and chemical weathering, and other processes, these nitrogenous compounds can move into the soil, just as other nutrients do.”

The Pinnacles of Gunung Mulu in Borneo are an example of where limestone rock weathering would be expected to produce significant levels of nitrogen. Credit: © Markus Loretto / Fotolia

These results significantly influence the science community to the point of editing the textbooks. “While there were hints that plants could use rock-derived nitrogen, this discovery shatters the paradigm that the ultimate source of available nitrogen in the atmosphere. Nitrogen is both the most important limiting nutrient on Earth and a dangerous pollutant, so it is important to understand the natural controls on its supply and demand. Humanity currently depends on atmospheric nitrogen to produce enough fertilizer to maintain world food supply. A discovery of this magnitude will open up a new era of research on this essential nutrient.” said Kendra McLauchlan, program director in the National Science Foundation’s Division of Environmental Biology, which co-funded the research.

Resources for Educators

  2. The nitrogen cycle
  3. Facts about Nitrogen
  4. C&EN: Rocks are a missing piece of the nitrogen cycle