The effects of earthworm invasion on stand-level carbon and nutrient cycling are poorly understood. Direct earthworm effects on soil carbon quantity and vertical distribution are hypothesized to have cascading effects on total belowground carbon flux (TBCF), soil respiration and heterotrophic activity. Over a worm invasion front in the Huron Mountains of Michigan, we quantified litterfall, soil respiration, soil carbon pools and root carbon pools.

Results/Conclusions

The plot at the leading edge of the invasion was characterized by much lower midden density, earthworm numbers and earthworm biomass, and forest floors with intact Oe and Oa horizons. Surprisingly, this plot exhibited higher soil respiration rates than plots with larger earthworm populations, whether those plots were invaded recently or for many years. This occurred despite the fact that there was a net loss of forest floor C that was not fully explained by increases in mineral soil C. In addition, root biomass increased in the more intensely invaded plots. Calculations of TBCF indicate that 60-75% less C is allocated belowground in all of the worm-invaded plots than in the low worm plot. Lower root production and mortality, mass-specific respiration rates or allocation to mycorrhizae are the likely components of this reduced TBCF. These TBCF estimates could be flawed if extremely high, non-steady state soil carbon loss rates are occurring in the low earthworm plots; or if DOC losses are very high in the higher earthworm plots. Future studies will explore these alternative hypotheses.