Removal of soil biota alters soil feedback effects on plant growth and defense chemistry

We examined how removal of soil biota affects plant-soil feedback (PSF) and defense chemistry of Jacobaea vulgaris, a native outbreak plant species in Europe that contains pyrrolizidine alkaloids (PAs), an important group of secondary plant compounds that mediate plant-insect interactions.Macrofauna and mesofauna, as well as fungi and bacteria were removed in a step wise approach by sieving watery extracts of soil through 1000 µm, 20 µm, 5 µm and 0.2 µm mesh sizes. The soil was either unplanted or had been used to grow J. vulgaris that was undamaged, or had been damaged by above- or belowground insect herbivores. The extracts were added to sterile soil and new plants were grown in the soil. Success of the sieving treatments were verified by molecular analysis of the inocula.