A rocky source of nitrogen

by Mary Caperton Morton
Tuesday, July 3, 2018

Calculations of the planet’s nitrogen balance have always been off: plants and soils seem to sequester far more nitrogen than expected. The atmosphere has long been thought of as the only major source of nitrogen, but a new study indicates an additional source: as much as a quarter of Earth’s terrestrial nitrogen may be supplied by eroding bedrock.

Nitrogen is one of the most abundant elements in the universe and the most abundant in Earth’s atmosphere, with molecular nitrogen composing 78 percent of the atmosphere. But this atmospheric abundance is still not enough to explain the vast amounts of nitrogen stored in plants, which use copious amounts in the form of ammonia and nitrate to fuel photosynthesis. This nitrogen is stored in plant cells and tissues and then recycled into soil when the plants decompose.

The new study in Science considers nitrogen balances in a variety of biological systems and geochemical cycles. Researchers led by Ben Houlton, of the University of California, Davis, found that as much as 26 percent of the nitrogen found in plants and soils comes from weathering of sedimentary and metasedimentary rocks such as sandstone and quartzite — a previously overlooked contribution to Earth’s terrestrial nitrogen balance.

“These results are going to require rewriting textbooks,” and they “open up a new era of research on this essential nutrient,” said Kendra McLauchlan, a program director at the National Science Foundation, which co-funded the research, in a statement.

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