Earthworm activity can alter forests' carbon-carrying capabilities : International

By Purdue University

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 CO