Purdue University scientists, along with researchers from the Smithsonian Institution and Johns Hopkins University, studied the effect of earthworms on forest chemistry by comparing carbon composition in forests that vary in earthworm activity.

They found forests with greater numbers of invasive earthworms tend to have litter and soil organic matter enriched in the plant material lignin. Sites with low numbers of the earthworms accumulate plant carbon in forms more easily degraded by bacteria.

Overall, the study found the amount of carbon in the litter and duff layer -- the surface mat of decaying organic matter and roots -- decreases because of earthworm activity.

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

The ongoing research was reported in a recent issue of The Journal of Geophysical Research.