Soil inoculum identity and rate jointly steer plant and belowground communities in the field

Inoculation with soil from different ecosystems can induce directional changes in plant and soil communities, however, it is unknown how specific these inoculations are, how much inoculum is needed, and whether different inocula collected from a similar ecosystem will steer differential ecosystem development at the recipient site. We conducted a soil inoculation experiment at a degraded grassland site and used two different soil inocula both from grasslands and three inoculation depths. We then measured the development of plant and soil communities over a period of three years. Our results show that soil and plant communities diverged and that these effects were stronger with increasing inoculation amount. Inoculation with upland meadow soil resulted in more complex biotic networks at the degraded site than inoculation with meadow steppe soil. Our experiment highlights that soil inoculation can promote restoration of degraded ecosystems but that the direction and speed of ecosystem development depend on the origin of the inoculum and the amount of inoculum used. One-Sentence Summary Soil inocula can promote restoration of degraded ecosystems but the direction and speed of ecosystem development depends on the soil identity and rate.