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Forest Feedback: Rising CO2 In Atmosphere Also Speeds Carbon Loss From Forest Soils, Research Finds

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"Forest Feedback: Rising CO2 In Atmosphere Also Speeds Carbon Loss From Forest Soils, Research Finds"

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Underappreciated player in carbon storage should be included in global change models, researcher says

Indiana University news release. Study here.

Research was conducted at Duke Forest Free Air CO2 Enrichment site, where pine trees were exposed to increased levels of CO2 for 14 years -- one of the world's longest-running CO2 enrichment experiments. (Credit: Will Owens)

Elevated levels of atmospheric carbon dioxide accelerate carbon cycling and soil carbon loss in forests, new research led by an Indiana University biologist has found.

The new evidence supports an emerging view that although forests remove a substantial amount of carbon dioxide from the atmosphere, much of the carbon is being stored in living woody biomass rather than as dead organic matter in soils.

Richard P. Phillips, lead author on the paper and an assistant professor of biology in the IU College of Arts and Sciences, said that after nearly two decades of research on forest ecosystem responses to global change, some of the uncertainty has been lifted about how forests are storing carbon in the wake of rising carbon dioxide levels.

It’s been suggested that as trees take up more carbon dioxide from the atmosphere, a greater amount of carbon will go to roots and fungi to acquire nutrients, but our results show that little of this carbon accumulates in soil because the decomposition of root and fungal detritus is also increased,” he said.

Carbon stored in soils, as opposed to in the wood of trees, is desirable from a management perspective in that soils are more stable over time, so carbon can be locked away for hundreds to thousands of years and not contribute to atmospheric carbon dioxide increases.

The research was conducted at the Duke Forest Free Air Carbon Dioxide Enrichment site in North Carolina. At this site, mature loblolly pine trees were exposed to increased levels of carbon dioxide for 14 years, making it one of the longest-running carbon dioxide enrichment experiments in the world. Researchers were able to calculate the age of the carbon cycling through the soil by growing roots and fungi into mesh bags that contained uniquely labeled soils. The soils were then analyzed for their organic composition.

The authors also report that nitrogen cycled faster in this forest as the demand for nutrients by trees and microbes became greater under elevated CO2.

“The growth of trees is limited by the availability of nitrogen at this site, so it makes sense that trees are using the ‘extra’ carbon taken up under elevated CO2 to prime microbes to release nitrogen bound up in organic matter,” Phillips said. “What is surprising is that the trees seem to be getting much of their nitrogen by decomposing root and fungal detritus that is less than a year old.”

The two-fold effects of microbial priming, where microbes are stimulated to decompose old soil organic matter via an increase in new carbon and other energy sources, and the faster turnover of recently fixed root and fungal carbon, are enough to explain the rapid carbon and nitrogen cycling that is occurring at the Duke Forest FACE site.

“We call it the RAMP hypothesis — Rhizo-Accelerated Mineralization and Priming — and it states that root-induced changes in the rates of microbial processing of carbon and nitrogen are key mediators of long-term ecosystem responses to global change,” Phillips added.

“Most ecosystem models have limited representations of roots, and none of them include processes such as priming. Our results demonstrate that interactions between roots and soil microbes play an underappreciated role in determining how much carbon is stored and how fast nitrogen is cycled. So including these processes in models should lead to improved projections of long-term carbon storage in forests in response to global environmental change’” he said.

Roots and fungi accelerate carbon and nitrogen cycling in forests exposed to elevated CO2” — by Phillips; IU and University of Gottingen (Germany) post-doctoral researcher Ina C. Meier; Emily S. Bernhardt of Duke University, A. Stuart Grandy and Kyle Wickings of the University of New Hampshire; and Adrien C. Finzi of Boston University — was published July 9 in the online early addition of Ecology Letters. Free access to the research article will be available until October.

Funding for this work was provided by the U.S. Department of Agriculture and the U.S. Department of Energy. Phillips and his research team in March received a $398,000 National Science Foundation grant to fund testing of the RAMP hypothesis in mixed hardwood forests of Indiana.

This piece was originally published at the Indiana University Newsroom.

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24 Responses to Forest Feedback: Rising CO2 In Atmosphere Also Speeds Carbon Loss From Forest Soils, Research Finds

  1. Soil organic material is about 60 percent carbon. Though highly fertile soils may contain only 1 to 3 percent organic material, a few kinds — in peat bogs or Arctic tundra — may be all compacted vegetation. In all, soil holds more than three times as much carbon as the amount found in aboveground vegetation or in the atmosphere. Carbon exists not only in living roots and myriad microbes, worms, fungi and other organisms that live on and near those plant parts, but also in accumulated material left behind by generations of plants that have come and gone.

    If the bank of carbon held in the world’s soils were to drop by just 0.3 percent, the release would equal a year’s worth of fossil fuel emissions. http://www.sciencenews.org/view/feature/id/337548/title/Soil’s_Hidden_Secrets

    • researchers built open-topped enclosures about 10 feet across around individual trees. Then they pumped in a continuous breeze of CO2, raising the concentration around the foliage to about 700 parts per million, a level expected within 70 years or so. (For comparison, 2011 levels were at 389 ppm, up from 275 ppm before the 19th century’s industrialization.)

      Periodically, the researchers pulled out cores of dirt up to 10 feet long, by driving hollow steel pipes as big around as a soup can into the soil by hand with a heavy slide hammer that banged the core sections down. After 11 years, the team dug up the trees. The tests revealed that when CO2 went up, the trees indeed grew more. But to the team’s surprise, carbon in the soil fell — by as much as 15 percent near the surface.

    • In 2007, in the Proceedings of the National Academy of Sciences, the researchers reported that soil microbes and fungi got busier right along with the thriving trees. The scientists call the process “priming,” but you might also call it serving appetizers. “Roots naturally exude what the microbes regard as food, including sugars,” Hungate says. “They do that even more when there is more CO2. But what happens is that while the bugs eat the new material, they also start eating the other stuff that has built up. It is like if I served you a soda with lunch, you’d start eating the table, too.” And when microbes eat organic matter, waste products include carbon dioxide and methane, which quickly make their way out of the soil and into the atmosphere.

    • Leaf and other surface litter, once believed to be the main way plant organic material gets into soil, is rapidly reduced to basic minerals by microbes before much of it can be incorporated deeply into the soil. Most of the fresh carbon enters soil deeper, released from living roots or left behind after roots themselves die.

  2. Wildfire and the Global Carbon Cycle

    Large fluxes of carbon into the atmosphere from wildfires can have an impact on the global carbon cycle, and with policy initiatives forming around carbon management and carbon budgets, researchers are scrambling to fill in the gaps regarding the role of fire in carbon emissions and sequestration. It has long been conventional wisdom that CO2 emissions were essentially neutral in global carbon fluxes since fires also promote vegetation regrowth and uptake of CO2. However, the more frequent and severe fires that the US and the world is experiencing as a result of climate change and fire suppression have made many begin to question whether that balance continues to exist.

    Oregon’s 2002 Biscuit Fire burned over 499,000 acres. In terms of CO2 emissions, the Biscuit Fire was also massive. Researchers estimate that the fire pumped 3.8 teragrams of Carbon into the atmosphere. That one fire equalled one third of all the carbon released through fossil fuel burning in Oregon annually.

    Bernard Bormann, a forest ecologist and soil scientist with the Pacific Northwest Research Station, has been looking at the effect of the Biscuit Fire on some long-term ecosystem productivity plots that were established in the Rogue River – Siskiyou National Forest in Oregon. Using comparison with a wealth of soils data collected before the fire, Bormman and his team estimate that previous studies used sampling and analysis methods that undercalculated the amount of carbon lost from soils by nearly 50% and the loss of nitrogen by 25%. These findings suggest that calculations and models of greenhouse gas emissions from wildfires may be seriously off the mark.

    Taken on the heels of similar studies across the western US and given the changes in fire regimes being observed across many regions, the study also raises important questions about the impacts severe fires have on the long-term role of forests in carbon sequestration.

    “It was shocking to see the changes to our plots one month after the Biscuit Fire,” says Bormann. ““There was nothing left after the fire—some snags and a few downed logs, almost bare soil. The whole soil structure had changed—it was crusty and would collapse when you walked on it. The soil organic matter was lost and even fine mineral particles from the upper soil layer were gone. We believe that the upper soil mineral layer may have been pulled into the atmosphere in the fire plume.”
    http://wildfirelessons.net/Additional.aspx?Page=145

    • Chris, that page looks like a complicated mixture of untested conventional wisdom and long-term land manager sacred truths, many contradicted by recent peer-reviewed research.

      What is the point of quoting and linking it here?

      “the changes to our plots one month after the Biscuit fire…”

      One month? Is that some kind of joke?

      • I don’t understand your point, the site is a valuable resource for science. If you follow the link in the article about the quote you cited you end up here http://www.sciencedaily.com/releases/2008/10/081016124041.htm

        • Where to start?

          My comments are related to being a sophisticated consumer (and communicator) of scientific information related to climate change.

          Science Daily is not a scientific journal. It is not a primary source of information on scientific research. It is a source of science-related news, one which I have found to be good in many ways, but also somewhat susceptible to the ‘cult of the new’ effect, wherein whatever is being reported is treated as something exciting and new.

          That’s valuable for building science-related readership, but it tends o be pretty sloppy intrms of sifting out solid research with lasting value from the announcement du jour which may be trivial or even wrong.

          2008 is pretty old in terms of a reference on definitive understanding of forest carbon storage. The field is moving fast, and because of the politics and economic implications of forest management practices, there tends to be a lot of noise and a lot of information with timber industry spin.

          That’s just the way it is. Those of us seeking facts and solid knowledge have to work through the scrum.

        • Joan Savage says:

          Bear in mind that the link supplied was to an opinion blog that led to a popular science review (Science Daily). That in turn leads to the original peer-reviewed article published in the Canadian Journal of Forest Research in 2008. Primary sources are preferred, and appreciated, all the better to distinguish the source from the non-peer reviewed commentary. Other than that, you were on a roll!

          Intense forest wildfire sharply reduces mineral soil C and N: the first direct evidence

          Bernard T. Bormann, Peter S. Homann, Robyn L. Darbyshire, Brett A. Morrissette

          http://www.nrcresearchpress.com/doi/abs/10.1139/X08-136

          • Joan Savage says:

            The Phillips et al. 2012 study abstract doesn’t mention tracking soil temperature in the root bags. Soil temperature is also a driver in tree root and their symbiont metabolism. It could be (could have been) monitored separately from the experimentally increased CO2.

        • The Wildfire “Lessons Learned Center” (LLC) is apparently part of the U.S. federal government wildfire bureaucracy. From their charter, on their web site:

          “The Interagency Lessons Learned Center (LLC) was approved by the FFALC in 2000 based on the need to improve safe work performance and organizational learning in wildland fire. The Center was staffed with a program manager in FY02 and the assistant program manager was funded in FY03. The LLC is located at the National Advanced Resource Technology Center (NARTC) in Arizona under the supervision of the NARTC Director. It serves a resource center for the wildland firefighter professional. It promotes a program of “train as you work and work as you train.” The LLC was modeled after the Center for Army Lessons Learned stemming from recommendations in the Business Practices Re-engineering for NARTC and the Tri-Data Study Phase III.”

          I also note the LLC was created during the Bush administration, when a heavy political hand was put on appointments in the civil service.

          In any case, the LLC is not an ecological research organization, nor a scientific research organization. It’s a kind of clearing house for technical information mainly related to fighting wildfire.

          The comments there on forest carbon sequestration are largely an aside from their primary mission.

          Note, as well, that the wildfire establishment in the US is broadly more aligned with the timber industry and preservation of forest economic values than it is with environmental or wilderness preservation interests.

          This is simply the reality of cultural alignments to date. Which do impact the “filtering” of information that the LLC states as one of its main missions.

  3. Paul Klinkman says:

    It’s like pulling teeth:

    What sequesters carbon ?

    How do we enhance the process ?

  4. h4x354x0r says:

    Can anyone here look over this graph I’ve made, that compares CO2 emissions vs. atmospheric CO2 PPM concentrations? I *think* I have the PPM concentrations indexed properly – i.e. at ~8GT emissions per year in 1958, if all of it stayed in the atmoshpere, we would see that year’s specific amount of increase in CO2 concentrations (~1ppm/year). But I’d like some feedback on this to confirm (or refute) the indexing of the CO2 concentrations.

    Any feedback (well not the carbon cycle feedback!) would be greatly appreciated.

    Graph: http://twitpic.com/a7z0xa

    • Joan Savage says:

      Compare your graphical estimate to Figure 3a in Church et al 2011. They did an integration of data on the fate of energy fluxes across time. Many versions of the Church 2011 graph have been reproduced, including here at Climate Progress.

      GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L18601, 8 PP., 2011
      doi:10.1029/2011GL048794

      Revisiting the Earth’s sea-level and energy budgets from 1961 to 2008

      http://www.agu.org/pubs/crossref/2011/2011GL048794.shtml

      • h4x354x0r says:

        Thanks for the link. Unfortunately, I don’t quite understand how to compare / translate the data presented there into what I’m trying to represent in the graph. I did find a citation to the following:

        Le Quéré, C., et al. (2009), Trends in the sources and sinks of carbon dioxide,Nat. Geosci., 2(12), 831–836, doi:10.1038/ngeo689

        That appears to hold the data I need to corroborate my graph, but it’s behind a paywall I don’t have access to. However, some other reports that reference that study do present some data that helps confirm the data in this graph.

        Another source: http://co2now.org/ indicates that about half of emitted carbon is staying in the atmosphere, and the other half is being absorbed right now.

        From these sources, it looks like the vertical position and scaling of the atmospheric CO2 PPM might be a little off, but… not by much. Also, I realize I haven’t actually added the PPM scale to the right of the graph.

        • Joan Savage says:

          Sorry, I was preoccupied by where the excess heat is stored, rather than the CO2.

          http://thinkprogress.org/climate/2011/09/23/327298/hottest-decade-deep-oceans-warming-may-be-on-its-way/

          • h4x354x0r says:

            Yeah, and the scary thing is the more heat the ocean absorbs, the less CO2 it can absorb. We’ve already seen that it’s absorption capabilities are degrading.

            So far atmospheric CO2 has only increased at a steady 1.1% acceleration rate. What I’m worried about is that we hit a “wall” of absorption capability, and suddenly we get HUGE increases in atmospheric CO2 instead of the steady rate we’ve seen so far.

            I haven’t been able to find any suggestion that “There’s a hard limit to that” – just a suggestion of a slowly accelerating degradation. If there’s a climate scientist saying “I think the earth can only absorb X GT of carbon emissions per year” I’d like to find that and read up on it.

  5. Mike Roddy says:

    Thanks for this, and for the comments.

    We don’t have many actual forests left in America, around 5% of what was once here. The rest have been destroyed or degraded, and “managed” for fiber production.

    Nature is the best at providing healthy soil and large scale carbon sequestration. Using the example of the Biscuit fire, much of the lower Illinois River area has been clearcut, raising local temperatures, reducing precipitation, and altering nutrient cycling and precipitation patterns. When the fire burned, it was much hotter and more destructive than what would have occurred in nature, from a combination of excessive “management” and fire suppression.

    The major forest disease here is destroying them for wood products. We need to build our homes out of inert materials, and allow our forests to regenerate naturally. Wood framing is a huge contributor to our annual emissions: tinyurl.com/yc8ncuq, tinyurl.com/ycxfsqu

  6. The Indiana research is interesting, but there seem to be a few immediate caveats for readers.

    - the posting appears to simply be a reprint of a press release

    - this kind of in-situ ecological research is really tricky, and results should be considered in the context of similar research by other scientists

    - even at 11 or 14 years, this research is very short term relative to the foods webs of an ancient forest.

    - more specifically, mesh bags of “uniquely labeled soils” are a sophisticated technique for tracking biochemical pathways, but it’s very hard if not impossible to have them match the interdependent microbial community of undisturbed native soils.

    - finally, a great deal of research has shown very wide differences between different kinds of forest ecosystem in terms of above ground versus underground carbon storage.

    Even to the extent these Indiana results are robust for the ecosystem studied, one should be very wary of generalizing them to other kinds of forest.

    • “…one should be very wary of generalizing them to other kinds of forest.”

      Why exactly?

      Your opinion is contradicting ongoing scientific research findings. Please read the first comment i posted above and the follow the link…

      “…soil microbes and fungi got busier right along with the thriving trees.” Hence more decomposing = more emissions outgas to the atmosphere.

  7. David Lewis says:

    We’re like Alice in Wonderland, after ingesting some of the mushroom, just as the first of its effects show up.

    One of the reasons Hansen cites when making his case everyone should be more concerned than they are is that the trigger that caused the ice age cycles was changes in solar insolation thought to be approximately 0.25 of a watt/m2 net effect. The bullet was CO2 and other GHG coming out of or going into the planetary system somewhere.

    He calls the planetary system at the temperature it was before the Anthropocene “incredibly sensitive”.

    He points out that the wastes of civilization are now the trigger, and the net effect at the moment is about 0.75 of a watt/m2.

  8. Joan Savage says:

    A gorilla-sized factor in soil carbon loss is warmer soil temperature, which speeds up decomposition rate.

    Consider that the tundra peat formed in conditions when the summer season generated biomass faster than it could be recycled and winter was long enough and cool enough to minimize decomposition.

    The news about how increased CO2 can accelerate soil carbon loss in a forest is somewhat separable from the effects o the temperature shift.
    I would have been more comfortable if the abstract had at least mentioned temperature monitoring to see how it factored into metabolic rate.

  9. Gail says:

    Any study of trees that doesn’t take into account the persistent, ubiquitous elevated and rising background level of tropospheric ozone will by definition be incomplete.

    from this post, July 14: http://witsendnj.blogspot.com/2012/07/anchors-away.html

    Remember, controlled fumigation experiments have proven that root systems of plants are damaged before any visible symptoms appear…and given that visible symptoms are now everywhere to be found (bare branches, thin crowns, splitting bark, injured foliage and needles) it’s a safe bet that something sinister has been going on underground for quite some time. Not only are impaired roots unable to anchor the earth in place, they aren’t soaking up water and returning it to the atmosphere via evapotranspiration from leaves. The ground becomes saturated more quickly when it rains, creating more run-off, and flooding.

    Speaking of dirt, it turns out there is a new study just released from a long-term research project at the Duke FACE facility, which has determined that soil isn’t sequestering the carbon they thought it would, and now they are shocked, shocked, shocked!

    “Richard P. Phillips, lead author on the paper and an assistant professor of biology in the IU College of Arts and Sciences, said that after nearly two decades of research on forest ecosystem responses to global change, some of the uncertainty has been lifted about how forests are storing carbon in the wake of rising carbon dioxide levels.”

    “‘It’s been suggested that as trees take up more carbon dioxide from the atmosphere, a greater amount of carbon will go to roots and fungi to acquire nutrients, but our results show that little of this carbon accumulates in soil because the decomposition of root and fungal detritus is also increased,’ he said.”

    Well, since they only considered elevated CO2 in their study and did nothing to factor in the influence of ambient ozone – which has been detrimental for fifty years in the North Carolina mountains where the study was done, due to upwind coal power plants and other industrial facilities – I guess it’s no wonder they conclude:

    “The two-fold effects of microbial priming, where microbes are stimulated to decompose old soil organic matter via an increase in new carbon and other energy sources, and the faster turnover of recently fixed root and fungal carbon, are enough to explain the rapid carbon and nitrogen cycling that is occurring at the Duke Forest FACE site.”

    “‘We call it the RAMP hypothesis — Rhizo-Accelerated Mineralization and Priming — and it states that root-induced changes in the rates of microbial processing of carbon and nitrogen are key mediators of long-term ecosystem responses to global change,’ Phillips added.”

    They call it RAMP, and I call it ozone poisoning. I think they forgot to read the definitive book on forest death from air pollution “An Appalachian Tragedy” so let’s leave them to their blinding CO2 obsession (to quote Paul Kingsnorth).

    • Joan Savage says:

      Ambient regional ozone (or other regional factors such as temperature) would affect both the control plots and test plots. The only variable in the test plots was added CO2. The researchers showed that CO2 addition alone significantly altered the root-fungi-soil relationship, over and above all the other stuff happening in the region.