Plants need enriched soil to make use of increasing carbon dioxide.
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By Amanda Mascarelli of Nature magazine
As carbon dioxide levels in the atmosphere continue to climb, most climate models project that the world’s oceans and trees will keep soaking up more than half of the extra CO2. But researchers report this week that the capacity for land plants to absorb more CO2 will be much lower than previously thought, owing to limitations in soil nutrients.
Because plants take up CO2 during photosynthesis, it has long been assumed that they will provide a large carbon ‘sink’ to help offset increases in atmospheric CO2 caused by the burning of fossil fuels. Some scientists have argued that the increase might even be good for plants, which would presumably grow faster and mop up even more CO2. Climate models estimate that the world’s oceans have absorbed about 30% of the CO2 that humans have released in the past 150 years and that land plants have gulped another 30%. But the latest study, by ecologists Peter Reich and Sarah Hobbie at the University of Minnesota in St Paul, suggests that estimates of how much CO2 land plants can use are far too optimistic. Plants also need soil nutrients, such as nitrogen and phosphorus, to grow. But few studies have tested whether soils contain enough of these nutrients to fuel growth in proportion to rising CO2.
“This work addresses a question that’s been out there for decades,” says Bruce Hungate, an ecosystem scientist at Northern Arizona University in Flagstaff. "It's a hard question to answer, because it takes a long time to see how ecosystem carbon and nitrogen cycles change."
Long-term growth
In a 13-year field experiment on 296 open-air plots, the researchers grew perennial grassland species under ambient and elevated concentrations of both atmospheric CO2 and soil nitrogen.
“Rather than building a time machine and comparing how ecosystems behave in 2070 — which is hard to do — we basically create the atmosphere of 2070 above our plots,” says Reich.
Reich and Hobbie found that from 2001 to 2010, grasses growing under heightened CO2 levels grew only half as much in untreated as in enriched nitrogen soils.
Researchers do not have a firm grasp on the complexities of nitrogen and carbon cycle interactions, so “the vast majority of models do not adequately reflect nutrient limitation”, says Adrien Finzi, a biogeochemist at Boston University in Massachusetts. “The real strength in this study is that now we have this 13-year record of a single ecosystem. It provides a really strong case for the claim that soil resources and nitrogen limitation in particular can impose a major constraint on carbon storage in terrestrial ecosystems.”
A study published in March modeled nutrient cycling across the globe to predict how much carbon plants could sequester over the next 100 years when nutrient limitations are taken into account. Those simulations, which included nitrogen limitations in northern hemisphere soils and phosphorus limitations in the tropics, predicted that land plants will absorb 23% less carbon than is projected by other models.
Researchers say that much more work is needed to understand how nutrient dynamics will affect carbon uptake — particularly in forest ecosystems, which are expected to be important carbon sinks. Often, says Hungate, these ecosystems seem to offer a “partial, natural, easy solution” to the climate problem. “But it turns out that in reality, ecosystems are complex and only have limited flexibility.”
This article is reproduced with permission from the magazine Nature. The article was first published on October 1, 2012.
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9 Comments
Add CommentAs usual, Priddseren knows more than all.
Reply | Report Abuse | Link to thisIt also appears that priddseren didn't bother to even glance at the scientific paper that Mascarelli linked to at the bottom of her writeup in Nature. If he had, he would see that the experiment was a comparison between plots of various plants with present-day CO2 and actual real plots given increased CO2, under conditions of various soil amendments. The plots were given ample years to adapt to the experimental conditions (though of course not enough time for much evolutionary adaptation of the plants).
Reply | Report Abuse | Link to thisPriddsren has a good point about the need to repeat this in different locations of the world. I expect that is underway already. Perhaps he should help with one of the next 13-year set of experiments.
http://dx.doi.org/10.1038/nclimate1694
This study is contradicted by a new study from Goethe University in Frankfurt, Germany suggests that the Umbrella Thorn Acacia trees will make a comeback.
Reply | Report Abuse | Link to thisTree trumps grass to rule the savannas
A new study published today in “Nature” by authors from the Biodiversity and Climate Research Centre and the Goethe University Frankfurt suggests that large parts of Africa’s savannas may well be forests by 2100. The study suggests that fertilization by atmospheric carbon dioxide is forcing increases in tree cover throughout Africa. A switch from savanna to forest occurs once a critical threshold of CO2 concentration is exceeded, yet each site has its own critical threshold. The implication is that each savanna will switch at different points in time, thereby reducing the risk that a synchronous shock to the earth system will emanate from savannas.
“In fact, only one experimental study has investigated how savanna plants will respond to changing CO2 concentrations and this study showed that savanna trees were essentially CO2 starved under pre-industrial CO2 concentrations, and that their growth really starts taking off at the CO2 concentrations we are currently experiencing.“
Other pertinent "World Report" studies can be found referenced here: GK
http://www.worldclimatereport.com/index.php/2011/03/23/global-greening-continues-did-we-cause-it/
G. Karst almost took the words out of my mouth. This study only looks as grasses, who's roots only penetrate so deep into soil, whereas trees contain 90% of their root system in the top 12 inches of soil with other roots going deeper, hence able to reach more nitrogen and other essential nutrients. I am not sure if the author or the paper itself, but a dis-service with climate change has been done with claiming carbon sinking is much lower than thought to be.
Reply | Report Abuse | Link to thisNothing in this study applies to MAN's grain production, where farmers ensure adequate nitrogen is available to our food crops. No one questions the resulting increase in yields, when N is not limiting. Man's food supply is only secure under warm, wet, increased fertilization of both CO2 and bio-absorbable nitrogen conditions. One should compare these results to crop yields during the LIA. GK
Reply | Report Abuse | Link to thisWhere to start?
Reply | Report Abuse | Link to thisGKarst: You are correct in stating that this study does not address food crops, it wasn’t intended to after all. It was intended to investigate the reaction of natural plant communities to increased co2 levels w/out human input of nutrients.
You sir are also correct when you state that trees trump grass, that is when you are referencing the over hybridized junk in the millions of sod-grass yards. Naturally occurring long and short perennial grasses and their associated communities equal and in a lot of cases surpass trees in usage and sequestration of co2.
Snells: Perhaps your post was a typographical error, not sure.
Perennial grasses have root systems that measure in multiple meters. Also, the depth of root a system is not an indicator of a plant’s ability to use nutrients in the soil, differing horizons will dictate the availability of nutrients at differing depths.
Prid: Do you realize that you read like a Fox News commentator? Are you?
If this study had been conducted with short life cycle organisms, then adaptation over a sixty year span would in fact be pertinent. The problem is that perennial grasses, both long and short, have life cycles measured in decades, in some cases centuries. Therefore, no adaptation. This is one of the greatest threats posed by human caused/aggravated climate change is the fact that very few species will be able to adapt over the pertinent time spans.
I am in agreement with you re projections of the future atmospheric conditions (as yet we have no time travel,) but that begs the question, “Do you plan for worse case or best case?” Myself, I prefer not being surprised, “plan for the worst and hope for the best.”
As to changing understanding of a given field of scientific endeavor, that’s part of the scientific method. Observe, hypothesize, experiment, incorporate experimental results, hypothesize….
billsmith: I doubt prid would do that. Seriously doubt he would be allowed to considering his closed thought processes.
Nagnoctic: If you find S.A. such a rag why are you here so much??
I proudly own left and green. If WE are wrong, you still end up with a healthier world and society. If YOU are wrong we all end up living a dark post-apocalyptic novel.
"If WE are wrong, you still end up with a healthier world and society. If YOU are wrong we all end up living a dark post-apocalyptic novel."
Reply | Report Abuse | Link to thisYou forget that most tragedy is caused by doing the wrong thing, at the wrong time. Scientists are not immune to this fact and have created tragedy acting on suspect data.
Any actions to reduce CO2, is a very dangerous action when world populations are 7 billion +. If world climate is cycling over a peak, into cooling, actions could turn downright catastrophic.
Remember also, models have a manual CO2 sensitivity input. Most empirical evidence indicates a sensitivity of 0.5 degrees per C or even lower. Only modeled results obtain high sensitivity results.
Think back... to plans to dust black carbon on the Arctic Ice in order to prevent the perceived cooling, of the time. Sometimes, the safe bet is to not jump to the left or right... but keep one's hands in one's pockets. GK
Think back... to plans to dust black carbon on the Arctic Ice in order to prevent the perceived cooling, of the time
Reply | Report Abuse | Link to thisWow. You are using the old "scientists were predicting global cooling in the 1970s" routine, at Scientific American?
There was a minor hypothesis with a total of 7 research papers exploring the idea that human emissions of aerosols might cause cooling. Meanwhile, there were 44 papers on global warming from human emissions of CO2.
6 times as many warming papers.
Compare 7 papers from 35 years ago to 10,000 papers behind the IPCC 2007 report and the thousands more since then.
If you read my comment, you will notice that I used the word "perceived". It matters not whether there was a legitimate basis for actions. In fact that is my point. What does matter, is that various plans were discussed, to mitigate or divert, a ice age cooling. This was only done on a "what if" basis... just like it is today.
Reply | Report Abuse | Link to thisYou state: "Compare 7 papers from 35 years ago to 10,000 papers behind the IPCC 2007 report and the thousands more since then."
You seem to ignore the fact that most of those papers were based on the same Global Climate Model, that is now failing. I hardly matters if there were a 100,000 papers, if they are based on the same modality.
One does not validate a hypothesis (model) by weighing the mass of papers linked to it. It is this type of validation which brings critical thinkers to be skeptical. If reality disagrees with the model, one does not repair reality. GK