1. Department of Soil Quality; Wageningen University; 6700 AA Wageningen The Netherlands
2. Estación Experimental de Zonas Áridas; Consejo Superior de Investigaciones Científicas; 04120 Almería Spain
3. Department of Environmental Studies; University of Delhi; Delhi 110 007 India
4. Plant-Soil Interactions; Research Division of Agroecology and Environmental Science; Agroscope; CH - 8046 Zürich Switzerland
5. Department of Evolutionary Biology and Environmental Studies; University of Zürich; CH - 8057 Zürich Switzerland
6. Plant-Microbe Interactions; Institute of Environmental Biology; Faculty of Science; Utrecht University Utrecht The Netherlands