What was done
At two extensively managed grassland sites in Thuringia/Germany, the authors studied the effects of anecic earthworms -- which generally inhabit a single vertical burrow throughout their entire lives that can be as much as five meters in depth, but is generally in the range of one to two meters -- on soil carbon stocks and turnover via analyses of enzyme activity, stable isotopes, nuclear magnetic resonance spectroscopy, and the ¹⁴C age of their burrow linings.

What was learned
The primary finding of the seven German scientists was that "the carbon distribution in soils is changed by anecic earthworms' activity with more carbon stored in the subsoil where earthworms slightly increase the carbon stocks." In this regard they also state that "the translocation of carbon from [the] organic layer to the subsoil will decrease the carbon vulnerability to mineralization," since "carbon in the organic layer and the surface soil is much more prone to disturbances with rapid carbon loss than subsoil carbon."

What it means
Since Don et al. note that "earthworms are present in almost all ecosystems around the globe with particularly high abundances in grasslands, where they increase productivity (Partsch et al., 2006)," and where "100-800 burrows per square meter have been reported by Lavelle (1988)," it is evident that their presence and activity play important roles in helping earth's soils store and preserve carbon ... and thereby mitigate the rate of rise of the atmosphere's CO2 concentration.

References
Lavelle, P. 1988. Earthworm activities and the soil system. Biology and Fertility of Soils 6: 237-251.

Partsch, S., Milcu, A. and Scheu, S. 2006. Decomposers (Lumbricadae, Collembola) affect plant performance in model grasslands of different diversity. Ecology 87: 2548-2558.