1. Plant Ecology Institute of Biology Freie Universität Berlin Altensteinstr. 6 D‐14195 Berlin Germany
2. Ecological Farming Systems Research Station ART Agroscope Reckenholz Tänikon Zürich Switzerland
3. Plant–Microbe Interactions Institute of Environmental Biology Faculty of Science Utrecht University 3508 TB Utrecht The Netherlands
4. Institute of Evolutionary Biology and Environmental Studies University of Zürich Zürich Switzerland
5. Department of Ecological Science Faculty of Earth and Life Sciences VU University Amsterdam The Netherlands
6. Department of Plant, Soil and Insect Science University of Massachusetts Amherst MA USA