The ability of forests to sequester carbon from the atmosphere depends on nutrients available in the forest soils, shows new research from an international team of researchers, including IIASA.
The study, published in the journal Nature Climate Change, showed that forests growing in fertile soils with ample nutrients are able to sequester about 30% of the carbon that they take up during photosynthesis. In contrast, forests growing in nutrient-poor soils may retain only 6% of that carbon. The rest is returned to the atmosphere as respiration.
“This paper produces the first evidence that to really understand the carbon cycle, you have to look into issues of nutrient cycling within the soil,” says IIASA Ecosystems Services and Management Program Director Michael Obersteiner, who worked on the study as part of a new international research project sponsored by the European Research Council.
Marcos Fernandez-Martinez, first author of the paper and researcher at the Center for Ecological Research and Forestry Applications (CREAF) and the Spanish National Research Council (CSIC) says, “In general, nutrient-poor forests spend a lot of energy-carbon-through mechanisms to acquire nutrients from the soil, whereas nutrient-rich forests can use that carbon to enhance biomass production.”
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By Eric Sorensen, WSU science writer
PULLMAN, Wash. – Researchers led by a Washington State University biologist have found that arid areas, among the biggest ecosystems on the planet, take up an unexpectedly large amount of carbon as levels of carbon dioxide increase in the atmosphere. The findings give scientists a better handle on the earth’s carbon budget – how much carbon remains in the atmosphere as CO2, contributing to global warming, and how much gets stored in the land or ocean in other carbon-containing forms.
“It has pointed out the importance of these arid ecosystems,” said R. Dave Evans, a WSU professor of biological sciences specializing in ecology and global change. “They are a major sink for atmospheric carbon dioxide, so as CO2 levels go up, they’ll increase their uptake of CO2 from the atmosphere. They’ll help take up some of that excess CO2 going into the atmosphere. They can’t take it all up, but they’ll help.”
Published in Nature Climate Change
The findings, published in the journal Nature Climate Change, come after a novel 10-year experiment in which researchers exposed plots in the Mojave Desert to elevated carbon-dioxide levels similar to those expected in 2050. The researchers then removed soil and plants down to a meter deep and measured how much carbon was absorbed.
“We just dug up the whole site and measured everything,” said Evans.
The idea for the experiment originated with scientists at Nevada’s universities in Reno and Las Vegas and the Desert Research Institute. Evans was brought in for his expertise in nutrient cycling and deserts, while researchers at the University of Idaho, Northern Arizona University, Arizona State University and Colorado State University also contributed.
Funding came from the U.S. Department of Energy’s Terrestrial Carbon Processes Program and the National Science Foundation’s Ecosystem Studies Program.
Vast lands play significant role
The work addresses one of the big unknowns of global warming: the degree to which land-based ecosystems absorb or release carbon dioxide as it increases in the atmosphere.
Receiving less than 10 inches of rain a year, arid areas run in a wide band at 30 degrees north and south latitude. Along with semi-arid areas, which receive less than 20 inches of rain a year, they account for nearly half the earth’s land surface.
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04 Mar 2014: Analysis
Soil as Carbon Storehouse:
New Weapon in Climate Fight?
The degradation of soils from unsustainable agriculture and other development has released billions of tons of carbon into the atmosphere. But new research shows how effective land restoration could play a major role in sequestering CO2 and slowing climate change.
In the 19th century, as land-hungry pioneers steered their wagon trains westward across the United States, they encountered a vast landscape of towering grasses that nurtured deep, fertile soils.
Today, just three percent of North America’s tallgrass prairie remains. Its disappearance has had a dramatic impact on the landscape and ecology of
The world’s cultivated soils have lost 50 to 70 percent of their original carbon stock.
the U.S., but a key consequence of that transformation has largely been overlooked: a massive loss of soil carbon into the atmosphere. The importance of soil carbon — how it is leached from the earth and how that process can be reversed — is the subject of intensifying scientific investigation, with important implications for the effort to slow the rapid rise of carbon dioxide in the atmosphere.
According to Rattan Lal, director of Ohio State University’s Carbon Management and Sequestration Center, the world’s cultivated soils have lost between 50 and 70 percent of their original carbon stock, much of which has oxidized upon exposure to air to become CO2. Now, armed with rapidly expanding knowledge about carbon sequestration in soils, researchers are studying how land restoration programs in places like the
Soil in a long-term experiment appears red when depleted of carbon (left) and dark brown when carbon content is high (right).
former North American prairie, the North China Plain, and even the parched interior of Australia might help put carbon back into the soil.
Absent carbon and critical microbes, soil becomes mere dirt, a process of deterioration that’s been rampant around the globe. Many scientists say that regenerative agricultural practices can turn back the carbon clock, reducing atmospheric CO2 while also boosting soil productivity and increasing resilience to floods and drought. Such regenerative techniques include planting fields year-round in crops or other cover, and agroforestry that combines crops, trees, and animal husbandry.
Recognition of the vital role played by soil carbon could mark an important if subtle shift in the discussion about global warming, which has been
A look at soil brings a sharper focus on potential carbon sinks.
heavily focused on curbing emissions of fossil fuels. But a look at soil brings a sharper focus on potential carbon sinks. Reducing emissions is crucial, but soil carbon sequestration needs to be part of the picture as well, says Lal. The top priorities, he says, are restoring degraded and eroded lands, as well as avoiding deforestation and the farming of peatlands, which are a major reservoir of carbon and are easily decomposed upon drainage and cultivation.
He adds that bringing carbon back into soils has to be done not only to offset fossil fuels, but also to feed our growing global population. “We cannot feed people if soil is degraded,” he says.
“Supply-side approaches, centered on CO2 sources, amount to reshuffling the Titanic deck chairs if we overlook demand-side solutions: where that carbon can and should go,” says Thomas J. Goreau, a biogeochemist and expert on carbon and nitrogen cycles who now serves as president of the Global Coral Reef Alliance. Goreau says we need to seek opportunities to increase soil carbon in all ecosystems — from tropical forests to pasture to wetlands — by replanting degraded areas, increased mulching of biomass instead of burning, large-scale use of biochar, improved pasture management, effective erosion control, and restoration of mangroves, salt marshes, and sea grasses.
“CO2 cannot be reduced to safe levels in time to avoid serious long-term impacts unless the other side of atmospheric CO2 balance is included,” Goreau says.
Scientists say that more carbon resides in soil than in the atmosphere and all plant life combined; there are 2,500 billion tons of carbon in soil, compared with 800 billion tons in the atmosphere and 560 billion tons in plant and animal life. And compared to many proposed geoengineering fixes, storing carbon in soil is simple: It’s a matter of returning carbon where it belongs.
Through photosynthesis, a plant draws carbon out of the air to form carbon compounds. What the plant doesn’t need for growth is exuded through the roots to feed soil organisms, whereby the carbon is humified, or rendered stable. Carbon is the main component of soil organic matter and helps give soil its water-retention capacity, its structure, and its fertility. According to Lal, some pools of carbon housed in soil aggregates are so stable that they can last thousands of years. This is in contrast to “active” soil carbon,
‘If we treat soil carbon as a renewable resource, we can change the dynamics,’ says an expert.
which resides in topsoil and is in continual flux between microbial hosts and the atmosphere.
“If we treat soil carbon as a renewable resource, we can change the dynamics,” says Goreau. “When we have erosion, we lose soil, which carries with it organic carbon, into waterways. When soil is exposed, it oxidizes, essentially burning the soil carbon. We can take an alternate trajectory.”
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