ORGANIC-MINERAL INTERACTIONS ALONG AN EARTHWORM INVASION CHRONOSEQUENCE

Soil organic matter (OM) plays an important role in mineral weathering and soil development, and the interaction of OM and minerals contribute to the soils’ capacity to stabilize carbon (C). Among many soil forming processes, bioturbation may strongly influence the interaction between mineral surfaces and SOC because it promotes contacts between OM and mineral surfaces. Earthworms, probably the best known bioturbators, are exotic species to areas previously glaciated. When they are introduced into these ecosystems they enhance bioturbation and thus change soil morphology and geochemical properties. We are studying the effects earthworms have on C stabilization through organo-mineral complexation along a 200 m long earthworm invasion chronosequence in a hardwood forest in northern Minnesota. This transect extends from soils where earthworms are absent to soils that have been invaded by earthworms for 30-40 years. Non-invaded soils have ~5 cm thick litter layers, thin (~5cm) A horizons, silt rich E horizon, and clay rich Bt horizons. The A and E horizons appear to have formed from Aeolian deposits, while the Bt horizons have developed from the underlying glacial till. With the advent of earthworms, the litter layer disappears and the A horizon expands at the expense of the O and E horizons. Carbon storages in the A horizon decrease with the arrival of invasive earthworms, but this trend is not consistent along the various stages of earthworm invasion: the storage is a multi-variate function of C concentration, soil bulk density, and A horizon thickness that vary differently over the sequence of earthworm invasion. Mineral’s specific surface area (SSA) in the A and E horizons are larger in invaded soils than in the non invaded soils, whereas greater portions of mineral SSA is coated with C in soils with active earthworm populations. The results suggest that not only the minerals’ capacity to complex OM but also actual intensity of the complexation are greater in the invaded soils. This growing data set, when ultimately combined with ongoing measurements of population dynamics of earthworms along the invasion transect, carbon-mineral associations, and dissolved organic C, will elucidate how and how much soils’ capacity to stabilize C is affected by burrowing organisms who are often the keystone species of given ecosystems.