Earthworm activity can alter forests' carbon-carrying capabilities

October 27, 2008

WEST LAFAYETTE, Ind. - Earthworms can change the chemical nature of the carbon in North American forest litter and soils, potentially affecting the amount of carbon stored in forests, according to Purdue University researchers.

The Purdue scientists, along with collaborators from the Smithsonian Institution and Johns Hopkins University, study the habits of earthworms originally brought to North America from Europe. They want to determine the earthworms' effect on forest chemistry by comparing carbon composition in forests that vary in earthworm activity.

Some earthworms eat fallen leaves and other plant material - the litter of the forest floor - while others eat roots or soil organic matter. This begins a decomposition process in which organic materials pass through the animals' digestive tracts and back into the soil.

The research team found that forests with greater numbers of invasive earthworms tend to have litter and soil organic matter enriched in the plant material lignin, which is typically harder for bacteria to decompose, said Purdue biogeochemist Timothy Filley. Sites with low numbers of these earthworms accumulate plant carbon in forms more easily degraded by bacteria.

Overall, the amount of carbon in the litter and duff layer, which is the surface mat of decaying organic matter and roots, decreases because of earthworm activity. However, the change in carbon chemistry may make it harder for soil organisms to decompose the carbon remains. After earthworms feed on forest litter, they take the carbon down into the soil and mix it in, potentially leading to a buildup of carbon in the soil.

"If the litter just stays on the surface of the soil, then it's likely that normal oxidation of organic matter happens and a lot of that carbon will just go into the atmosphere," said Cliff Johnston, a Purdue environmental chemist and professor of agronomy. "However, if carbon can bind to the soil particles, such as clay, it might be a long-term way of stabilizing carbon."

Another way earthworm activity may affect the fate of carbon and the environment is in the thickness of layers of leaves and debris left on forest floors. Bare soil is generally very dark, absorbing more sunlight, which may dry it out quickly. A layer of lightly colored leaves is moderately reflective and holds moisture near the soil. Either condition may affect factors such as the warming of forest soil and the timing of snowmelt.

"Ultimately, we will look at such things to determine the potential invasive earthworms have in changing the flux of CO2 out of the forest and how much that could impact climate change," said Filley, who also is an associate professor of earth and atmospheric sciences.

The earthworms that the team studies were brought to North America by early European colonists, probably in the ships' ballasts or in plant soil. In northern North American forests the settlers found land devoid of such creatures because the worms never reoccupied soils formed when the glaciers melted.

In addition, earthworms don't move very fast. It's estimated they have migrated under their own power only about 100-200 kilometers in the past 10,000 years since the glaciers.

"In some forests, such as ones we are working at in northern Minnesota, we find soils where earthworms are only now being introduced." Filley said. "The main agents of introduction in such areas are discarded fishing bait in nearby lakes, transport between forest sites in tire treads and the movement of soil."

The research team reported findings of their ongoing study in a recent issue of the Journal of Geophysical Research. The National Science Foundation has provided funds to continue the work.

For this study, Filley, Johnston and their collaborators monitor earthworm activity at the Smithsonian Environmental Research Center forest area in Maryland. The scientists set up plots in which they manipulate the amount of litter on the ground and watch how fast the worms remove it.

In some areas of the forest, more than 350 worms can be found in one square meter.

"The impact of that many worms is huge for the forest ecosystem as from spring to fall they actively consume litter and mix it into the soil, leaving only a bare surface by year's end." Filley said.

In contrast, sites that have no earthworms have many years of accumulated litter and organic matter above the soil. This has implications for plant seed germination, water holding capacity and infiltration of the forest floor, among other things.

"The earthworms fundamentally change how the microbial community is decomposing," Filley said. "When they eat roots, they also eat other organisms that help to distribute nutrients between plants. Worms may throw off the timing of nutrient delivery."
Other members of the research team are Melissa McCormick and Dennis Whigham, both of the Smithsonian Environmental Research Center; Susan Crow of the Purdue Department of Earth and Atmospheric Sciences and now at Queen's University Belfast, UK; Katalin Szlavecz of the Johns Hopkins Department of Earth and Planetary Sciences; and Ronald van den Heuvel, formerly of the Smithsonian center and now at Landscape Ecology, Institute of Environmental Biology, Utrecht University, Netherlands. Both Johnston and Filley are members of the Purdue Climate Change Research Center.

Contact: Beth Forbes, (765) 494-2722,

Sources: Timothy Filley, (765) 494-6581,

Cliff Johnston, (765) 496-1716,


Earthworms' appetites may facilitate carbon storage so the chemical isn't released into the atmosphere as CO2, which potentially could help curb climate change. Tim Filley, a Purdue University environmental chemist, checks one of the plots at the Smithsonian Environmental Research Center in Maryland, where he and Cliff Johnston, another Purdue environmental chemist, monitor how much and how fast the worms eat leaves and other materials on the forest floor. This is part of a National Science Foundation-funded collaborative study by Purdue, Johns Hopkins University and the Smithsonian Institution. (Photo courtesy of Cliff Johnston, Purdue University Department of Agronomy)

A publication-quality photo is available at



A publication-quality photo is available at

Abstract on the research in this release is available at:

Purdue University

Related Carbon Articles from Brightsurf:

The biggest trees capture the most carbon: Large trees dominate carbon storage in forests
A recent study examining carbon storage in Pacific Northwest forests demonstrated that although large-diameter trees (21 inches) only comprised 3% of total stems, they accounted for 42% of the total aboveground carbon storage.

Carbon storage from the lab
Researchers at the University of Freiburg established the world's largest collection of moss species for the peat industry and science

Carbon-carbon covalent bonds far more flexible than presumed
A Hokkaido University research group has successfully demonstrated that carbon-carbon (C-C) covalent bonds expand and contract flexibly in response to light and heat.

Metal wires of carbon complete toolbox for carbon-based computers
Carbon-based computers have the potential to be a lot faster and much more energy efficient than silicon-based computers, but 2D graphene and carbon nanotubes have proved challenging to turn into the elements needed to construct transistor circuits.

Cascades with carbon dioxide
Carbon dioxide (CO(2)) is not just an undesirable greenhouse gas, it is also an interesting source of raw materials that are valuable and can be recycled sustainably.

Two-dimensional carbon networks
Lithium-ion batteries usually contain graphitic carbons as anode materials. Scientists have investigated the carbonic nanoweb graphdiyne as a novel two-dimensional carbon network for its suitability in battery applications.

Can wood construction transform cities from carbon source to carbon vault?
A new study by researchers and architects at Yale and the Potsdam Institute for Climate Impact Research predicts that a transition to timber-based wood products in the construction of new housing, buildings, and infrastructure would not only offset enormous amounts of carbon emissions related to concrete and steel production -- it could turn the world's cities into a vast carbon sink.

Investigation of oceanic 'black carbon' uncovers mystery in global carbon cycle
An unexpected finding published today in Nature Communications challenges a long-held assumption about the origin of oceanic black coal, and introduces a tantalizing new mystery: If oceanic black carbon is significantly different from the black carbon found in rivers, where did it come from?

First fully rechargeable carbon dioxide battery with carbon neutrality
Researchers at the University of Illinois at Chicago are the first to show that lithium-carbon dioxide batteries can be designed to operate in a fully rechargeable manner, and they have successfully tested a lithium-carbon dioxide battery prototype running up to 500 consecutive cycles of charge/recharge processes.

How and when was carbon distributed in the Earth?
A magma ocean existing during the core formation is thought to have been highly depleted in carbon due to its high-siderophile (iron loving) behavior.

Read More: Carbon News and Carbon Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to