Steering root-associated microbiomes via direct and soil legacy effects of neighbours

The composition of the root-associated microbiome of a host plant is thought to be strongly influenced by its host plant. However, this microbiome can also be steered by other plants, either directly, when the roots of a neighbour plant stimulate or suppress particular microbes or indirectly, when one plant influences the soil microbiome first and another plant grows in this soil later. How important these effects are of other plants and what the consequences are for the focal plant is not known. Here, we determine the relative importance of direct effects and indirect effects through soil legacies of (other) neighbouring plants on the root-associated microbiome of different focal plants using a grass, Phleum pratense, a forb, Cichorium intybus and two legumes, Trifolium pratense and Trifolium repens.