Declining nitrogen availability reduces CO2 fertilization effects

Nov 16, 2010 By Ron Walli

Climate models that project future atmospheric carbon dioxide concentrations should include a coupled nitrogen cycle, a team of researchers led by Oak Ridge National Laboratory has concluded.

In the past, coupled climate carbon cycle models have ignored feedback from the , but scientists have long speculated that the inevitable nitrogen limitation of production would reduce the widely reported carbon dioxide fertilization effect on trees. Now they have data to support their theory and the results are published in the .

"We now have a longer data record from the ORNL free-air CO2 enrichment experiment, and we report that the response of forest production to elevated CO2 has declined over time, a significant change from our previous observations," said Rich Norby, lead author of the paper and a member of ORNL's Environmental Sciences Division.

Previous research performed at ORNL and three other forested free-air CO2 enrichment, or FACE, experiments had shown a sustained increase in forest production in response to elevated levels of atmospheric CO2. While those increases matched projections of models used in the last Intergovernmental Panel on Climate Change assessment, this may have been misleading.

"Climate change models need to include a coupled nitrogen cycle if we are to have confidence in their predictions," Norby said.

During the first six years of the FACE experiment at ORNL, researchers observed a 23 percent increase in forest growth under elevated CO2, but the stimulation in growth, or net primary productivity, under elevated CO2 declined to 9 percent in 2008. As a result, global analyses that assume a sustained carbon dioxide fertilization effect are no longer supported by the FACE experiment, according to the PNAS publication.

"Our nitrogen budget analysis supports the premise that nitrogen availability was limiting to tree growth and declining over time, an expected consequence of stand development, and this was exacerbated by elevated CO2," Norby said.

The Department of Energy's FACE experiment at ORNL consisted of three plots of sweetgum trees that were control sites and two plots of trees that were exposed to levels of carbon dioxide projected in 2050 (550 parts per million). The experiment ran for 12 years and resulted in numerous scientific findings and several dozen publications.

Explore further: Pact with devil? California farmers use oil firms' water

More information: Co-authors of the paper, titled "CO2 Enhancement of Forest Productivity Constrained by Limited Nitrogen Availability," from ORNL are Jeffrey Warren and Colleen Iversen of the Environmental Sciences Division.

Related Stories

Forest response project FACEs the end

Jul 28, 2009

After 12 years, an experiment focused on forest growth and climate change comes to an end, and researchers at Oak Ridge National Laboratory are eager to collect and analyze data to see if their predictions match results.

Study finds trees not so large carbon sinks

Oct 27, 2010

The capacity of trees to counter rising carbon dioxide levels in the atmosphere may not be as great as previously thought, according to a new study with significant implications for predicting future climate ...

Soil nutrition affects carbon sequestration in forests

Dec 13, 2006

On December 11, USDA Forest Service (FS) scientists from the FS Southern Research Station (SRS) unit in Research Triangle Park, NC, along with colleagues from Duke University, published two papers in The Pr ...

Study: Forest productivity hiked by CO2

Dec 09, 2005

An Oak Ridge National Laboratory study in Tennessee suggests forest productivity may be significantly greater in an atmosphere enriched with carbon dioxide.

Recommended for you

Gimmicks and technology: California learns to save water

Jul 03, 2015

Billboards and TV commercials, living room visits, guess-your-water-use booths, and awards for water stinginess—a wealthy swath of Orange County that once had one of the worst records for water conservation ...

Cities, regions call for 'robust' world climate pact

Jul 03, 2015

Thousands of cities, provinces and states from around the world urged national governments on Thursday to deliver a "robust, binding, equitable and universal" planet-saving climate pact in December.

Will climate change put mussels off the menu?

Jul 03, 2015

Climate change models predict that sea temperatures will rise significantly, including in the tropics. In these areas, rainfall is also predicted to increase, reducing the salt concentration of the surface ...

As nations dither, cities pick up climate slack

Jul 02, 2015

Their national governments hamstrung by domestic politics, stretched budgets and diplomatic inertia, many cities and provinces have taken a leading role—driven by necessity—in efforts to arrest galloping ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

3 / 5 (2) Nov 16, 2010
"In the past, coupled climate carbon cycle models have ignored feedback from the nitrogen cycle,"

Um, why would they do that? What else are they ignoring that is needed for accurate models? Next thing their going to say is you can't include what we "don't know about". But do we even know what we don't know about?
2.3 / 5 (3) Nov 16, 2010
It seems that since net primary tree production fell from 23% to 9%, for a single year, they deduce it must be nitrogen limitation. Funny how we don't hear how great CO2 is for forest production until that production apparently falters. In any case, it is clear that at least some fundamentals remain a mystery.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.