Earthworms are ecosystem engineers that cause a long cascade of ecological effects when they invade previously earthworm-free forests. However, the consequences of earthworm invasion for soil microbial functions are poorly understood. Here, we used two well-studied invasion fronts of European earthworms in northern North American hardwood forests previously devoid of earthworms in order to investigate three stages of earthworm invasion: uninvaded, the front of the leading edge of earthworm invasion and locations invaded at least 10 years previously. Soil microbial biomass, respiration and metabolic quotient were measured. Earthworms had marked effects on soil microbial biomass (-42%) and respiration (-32%). At both sites, impacts were most pronounced at the leading edge of the invasion front, significantly decreasing soil microbial C use efficiency. This was most likely due to the disturbance of the soil microbial community caused by water stress. Based on these results, we hypothesize that effects of earthworm invasion on native soil ecosystem functioning are most pronounced at the peak of the invasion wave. After experiencing this wave, ecosystems possibly enter a new steady state with altered biotic compositions and functions.
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Acknowledgments We thank Cindy Buschena, Montara Roberts and Susan Barrott (all University of Minnesota, USA) for their help during the processing of soil samples. Further, we thankIngridKleinhansandStefanScheu(UniversityofGöttingen, Germany) for their key role in this study by measuring soil microbial parameters. Comments of two reviewers helped to improve the paper. Nico Eisenhauer gratefully acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Ei 862/1-1). JiˇríSchlaghamersky´ gratefully acknowledges funding by the Ministry of Education, Youth and Sports of the Czech Republic (Research Plan MSM0021622416) and by the Fulbright Program (stating that neither the Government of the United States nor any agency representing it has endorsed the conclusions or approved the contents of this publication).
- Ecosystem change
- Exotic earthworms
- Forest floor
- Microbial biomass
- Microbial respiration
- Northern hardwood forests