Rock nitrogen lets trees soak up more carbon dioxide

Futurity: Given that carbon dioxide is the most important climate-change gas, the nitrogen in rocks could significantly affect how rapidly the Earth will warm in the future, researchers say. If trees can access more nitrogen than previously thought, that could lead to more storage of carbon on land and less carbon remaining in the atmosphere, according to a new study published in Science.

“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 Benjamin Houlton, assistant professor of terrestrial biochemistry at University of California, Davis and co-author of the study. “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.”

Nitrogen, found in DNA and protein, is necessary for all life, is used worldwide as a fertilizer for food crops, and is the nutrient that most often limits plant growth in natural ecosystems. It was previously believed that nitrogen could only enter ecosystems from the atmosphere—either dissolved in rainwater or biologically “fixed” or assimilated by specialized groups of plants and other organisms. Because the amount of nitrogen in these atmospheric pathways is limited, it was thought that most ecosystems could not get enough to facilitate plant growth at maximum rates.

Following this line of thought, it was estimated that the nitrogen contribution from rocks in Northern California was on the same order as atmospheric nitrogen sources, made available through fixation and deposited via rainwater. “To put it in perspective, there is enough nitrogen contained in one inch of the rocks at our study site to completely support the growth of a typical coniferous forest for about 25 years,” says co-author Randy Dahlgren, professor of soil science.

“This nitrogen is released slowly over time and helps to maintain the long-term fertility of many California forests,” Dahlgren says. “It is also interesting to consider that the nitrogen in the rocks from our study site originates from the time of the dinosaurs, when plant and animal remains were incorporated into the sediments that eventually formed the rocks.”...

A path by the River Plym, shot by Derek Harper, Wikimedia Commons via Geograph UK, under the Creative Commons Attribution-Share Alike 2.0 Generic license