Nitrogen in rocks could help counter climate change

Posted by Emma Woollacott

Researchers have discovered that forest trees can tap into the nitrogen found in rocks, boosting their growth and allowing them to take up more carbon dioxide from the atmosphere.

The nitrogen in rocks could therefore significantly affect how rapidly the Earth warms in future, says the University of California, Davis team.

"We were really shocked; everything we’ve ever thought about the nitrogen cycle and all of the textbook theories have been turned on their heads by these data," says biogeochemist Professor Benjamin Houlton.

"Findings from this study suggest that our climate-change models should not only consider the importance of nitrogen from the atmosphere, but now we also have to start thinking about how rocks may affect climate change."

It was previously believed that nitrogen could only enter ecosystems from the atmosphere - either dissolved in rainwater or biologically 'fixed' by specialized groups of plants and other organisms.

However, says the team, there's enough nitrogen contained in one inch of the rocks at the study site to completely support the growth of a typical coniferous forest for about 25 years.

"This nitrogen is released slowly over time and helps to maintain the long-term fertility of many California forests,” says biogeochemist  Professor Randy Dahlgren.

In fact, forests growing on nitrogen-rich rock were about 50 percent more productive than those growing on nitrogen-poor rocks throughout Northern California and into Oregon.

The researchers found that the nitrogen isotopes in the rock matched those of the soils and trees, confirming that the nitrogen was coming from the rocks.

"It was like a fingerprint; we found the culprit, and it was the nitrogen in the rocks," says graduate student Scott Morford.

Since nitrogen tends to be highest in sedimentary rocks - which cover roughly 75 percent of the Earth’s land surface - the discovery has tremendous global significance, says the team.

"The stunning finding that forests can also feed on nitrogen in rocks has the potential to change all projections related to climate change," says Houlton.

"This discovery may also help explain several other studies that have found that the nitrogen 'budgets' of forests are out of balance, the nitrogen accumulation in their soil and plants being substantially greater than the apparent nitrogen inputs."

Researchers now include nitrogen in their climate-change models, and some indicate that it could cause an additional increase in global temperatures of up to 1.8 degrees Fahrenheit, as it limits the amount of carbon dioxide that plants can extract from the atmosphere.

If more nitrogen is available than predicted from the traditional nitrogen-cycling pathways, as the UC Davis study suggests, it could lead to more carbon storage on land and less carbon remaining in the atmosphere.