It seems trees have the ability to tap into nitrogen found in rocks, boosting the trees’
growth and their ability to pull more carbon dioxide from the
That's good news in the short term. Carbon dioxide is the greenhouse gas most are worried about so that means nitrogen in rocks can significantly affect how rapidly the earth will warm in
the future, the U.C. Davis researchers say.
“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 Professor Benjamin Houlton, a biogeochemist and one of the Nature study’s
co-authors. “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.”
“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,” said Professor Randy Dahlgren, a
biogeochemist and a study co-author. “This nitrogen is released slowly over time and helps to maintain the
long-term fertility of many California forests,” Dahlgren said. “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 study, led by Scott Morford, a graduate student in the
Department of Land, Air and Water Resources, focused on measuring the nitrogen
in rocks, soils and plants, and found that rocks enriched in nitrogen have a
profound effect on the fertility of forests.
Data from the study indicate that the amount of carbon stored in forest
soils derived from the nitrogen-rich bedrock was nearly twice that of sites
associated with nitrogen-poor rocks in Northern California. Furthermore, the
researchers used the inventory of forest growth data from the National Forest
Service to determine that this was not just a localized effect. In fact, the
productivity of forests growing on nitrogen-rich rock was approximately 50
percent higher than the productivity of forests growing on nitrogen-poor rocks
throughout Northern California and into Oregon.
“We were all stunned when the data showed that the nitrogen in the trees
was extremely high in forests that were living on the rocks with high nitrogen,”
To confirm the link between the nitrogen in the trees and that in the
surrounding rock, the researchers traced the nitrogen from the rocks using the
different isotopes of nitrogen. They 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,” Morford said.
The researchers stress that, since nitrogen tends to be elevated in rocks
of sedimentary origin, which cover roughly 75 percent of the Earth’s land
surface, the discovery that bedrock nitrogen has the potential to stimulate
forest productivity and carbon storage has tremendous global
“The stunning finding that forests can also feed on nitrogen in rocks has
the potential to change all projections related to climate change,” said
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.”
Houlton noted that nitrogen is becoming increasingly important in
climate-change studies and researchers have begun to incorporate nitrogen in
their climate-change models. Some models indicate that the nutrient could cause
an additional increase in global temperatures of up to one degree Celsius (1.8
degrees Fahrenheit) by 2010, as it limits the amount of carbon dioxide that
plants around the world 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.
The researchers call for further studies in other parts of the world to
determine if nitrogen in rocks affects forests outside of the Pacific
Morford is continuing his research and during the past year has collected
more than 800 rocks from Oregon to San Diego. A goal of this future research is
to determine how fast nitrogen is released from rocks under the varying
environmental conditions in California and beyond.
This study was funded by the Andrew W. Mellon Foundation, the Packard
Foundation, and the Kearney Foundation for Soil Science.