Does soil inoculation truly steer the composition of native soil communities?

Abstract

Soil inoculation is a promising tool for restoring degraded ecosystems, that is based on the assumption that introduced soil communities establish in the new environment and create positive feedback with new plant communities. However, we lack empirical evidence on the extent to which the soil community present in the relatively small amount of inoculated soil can truly alter the recipient or native soil community in the field. For the first time, we measured the soil community in both the inoculated and in the underlying soil layers in a whole-soil inoculation experiment in a restoration grassland. Within the inoculated layer, nematode and bacterial communities became increasingly similar to the donor soil community. However, in the soil layer beneath the inoculated layer, the similarity of the native bacterial and nematode communities to the donor community did not change significantly over time. Only the native fungal community gradually shifted towards the community present in the donor meadow. Our study provides conclusive field evidence that soil inoculation can restructure soil biota at the recipient site, but this effect is largely restricted to the inoculated soil layer. This challenges the commonly held assumption that soil inoculation drives changes in native soil communities through positive plant-soil feedbacks.