Inoculation of an ecosystem engineer (Earthworm: Lumbricus terrestris) during experimental grassland restoration: Consequences for above and belowground soil compartments

Although soil organisms might strongly affect the dynamics and composition of natural vegetation, relatively few studies have tried to in-situ manipulate soil fauna, especially in restoration ecology. The objective of this study was thus to observe the impact of a soil ecosystem engineer (Lumbricus terrestris L.) on plant communities as well as on soil organisms (springtails) in a reclaimed floodplain previously devoid of earthworms. Within a randomized factorial design based on buried frames (depth 0.45 m), half of the quadrats (1 m2) were inoculated with 100 earthworms, the other half served as control. After one year of experiment, earthworm inoculation doubled the plant biomass and favored grass species over forbs. Both abundance and diversity of Collembola (depending on functional groups) were negatively impacted by the presence of earthworms. Using a path analysis we found that this negative impact was probably indirect and due to an earthworm effect on plant community structure and plant functional groups. We suggest in our particular case that vegetation, and more precisely plant biomass and functional traits, may be more influential than soil properties in driving Collembola assemblages. Regarding restoration, we conclude that manipulating earthworms could be an interesting tool for increasing plant productivity but may disfavor soil biodiversity and alter above-belowground linkages.