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Soil Won't Save Us
By Betsy Mason
ScienceNOW Daily News
16 March 2007
As atmospheric carbon dioxide levels rise, scientists have counted on the ground beneath our feet to soak up some of this greenhouse gas. But fungi living in the soil could throw a wrench into that plan, according to a new study, which finds that the microbes could actually cause soil to lose carbon to the atmosphere.
Plants grow faster as CO2 levels increase, taking up more carbon from the air. Scientists have suggested that this might in turn cause soils to soak up excess carbon as well by accumulating more root matter.
To test this idea, a team of microbial ecologists and plant physiologists at the Smithsonian Environmental Research Center in Edgewater, Maryland, subjected a scrub oak ecosystem in Florida to twice the current level of atmospheric carbon dioxide for 6 years. The team was surprised to find that in spite of increased plant growth, the soils were losing carbon rather than taking up more. In fact, the soil was releasing more than half the amount of carbon dioxide that the plants were taking up.
The problem appears to be fungi. When the researchers compared the soil in the CO2-enriched environment to a similar plot that had been exposed to ambient CO2 for 6 years, they found that the high-CO2 plot had more fungi. Soil fungi are good at decomposing tough organic materials, explains team leader Karen Carney, in part by producing carbon-degrading enzymes. So increasing the amount of fungi boosts the decomposition of organic matter in the soil, releasing the stored carbon into the atmosphere through respiration. The findings appear online this week in the Proceedings of the National Academy of Sciences.
"This is not good news," says ecologist Richard Gill at Washington State University, Pullman. Most climate models assume that soil and vegetation will continue taking up at least as much carbon as before, if not more, he notes. Although a few other papers have shown that soil might become a source of carbon rather than a sink, this study takes an important step further by demonstrating a mechanism, Gill notes. If the microbial changes Carney's team discovered are indeed common to many habitats, their collective impact on global warming could be substantial, says ecologist Chris Field of the Carnegie Institution at Stanford University. "What this means is a subsidy we have been counting on won't be there in the future," he says.
By Betsy Mason
ScienceNOW Daily News
16 March 2007
As atmospheric carbon dioxide levels rise, scientists have counted on the ground beneath our feet to soak up some of this greenhouse gas. But fungi living in the soil could throw a wrench into that plan, according to a new study, which finds that the microbes could actually cause soil to lose carbon to the atmosphere.
Plants grow faster as CO2 levels increase, taking up more carbon from the air. Scientists have suggested that this might in turn cause soils to soak up excess carbon as well by accumulating more root matter.
To test this idea, a team of microbial ecologists and plant physiologists at the Smithsonian Environmental Research Center in Edgewater, Maryland, subjected a scrub oak ecosystem in Florida to twice the current level of atmospheric carbon dioxide for 6 years. The team was surprised to find that in spite of increased plant growth, the soils were losing carbon rather than taking up more. In fact, the soil was releasing more than half the amount of carbon dioxide that the plants were taking up.
The problem appears to be fungi. When the researchers compared the soil in the CO2-enriched environment to a similar plot that had been exposed to ambient CO2 for 6 years, they found that the high-CO2 plot had more fungi. Soil fungi are good at decomposing tough organic materials, explains team leader Karen Carney, in part by producing carbon-degrading enzymes. So increasing the amount of fungi boosts the decomposition of organic matter in the soil, releasing the stored carbon into the atmosphere through respiration. The findings appear online this week in the Proceedings of the National Academy of Sciences.
"This is not good news," says ecologist Richard Gill at Washington State University, Pullman. Most climate models assume that soil and vegetation will continue taking up at least as much carbon as before, if not more, he notes. Although a few other papers have shown that soil might become a source of carbon rather than a sink, this study takes an important step further by demonstrating a mechanism, Gill notes. If the microbial changes Carney's team discovered are indeed common to many habitats, their collective impact on global warming could be substantial, says ecologist Chris Field of the Carnegie Institution at Stanford University. "What this means is a subsidy we have been counting on won't be there in the future," he says.
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