A new addition to the terrestrial nitrogen cycle

This post contributed by Lindsay Deel, a Ph.D. student in geography at West Virginia University and Intern with ESA’s journal Frontiers in Ecology and the Environment
Memorizing diagrams of the nitrogen cycle – complete with all the little arrows flowing between atmospheric sources to uptake by vegetation – is a rite of passage for most undergraduate ecology students.  Now, following a new study published in the journal Nature, the diagrams will need to include a new little arrow flowing from bedrock sources to vegetation.  This could have dramatic implications for understanding the growth potential – and therefore, the carbon sequestration potential – of forested ecosystems.

Nitrogen is often cited as the most limiting nutrient for the growth of trees, so if forests can access more nitrogen, there is greater growth potential – and more growth means more carbon storage.

“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,” said Benjamin Houlton, Assistant Professor of Terrestrial Biogeochemistry, in a UC Davis press release about 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.”

Scientists have long thought that nitrogen could only enter forest ecosystems through the atmosphere – by deposition or biological fixation.  Based on this assumption, the UC Davis scientists expected to find, at most, the same nitrogen contribution from rocks.

“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,” explained Randy Dahlgren, a biogeochemist and study co-author, in the UC Davis press release.  “This nitrogen is released slowly over time and helps to maintain the long-term fertility of many California forests. 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.”

The discovery of such a substantial pool of stored nitrogen that is directly accessible to plants also sheds new light on the infamous “missing carbon sink,” which is assumed to be terrestrial.  Indeed, research related to nitrogen cycling will change because of this finding – as will the diagrams of nitrogen cycling in undergraduate ecology textbooks.


Photo: Mountain deep forest by Paolo Neo

Author: Nadine Lymn

ESA Director of Public Affairs

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