1. Centre for Microbial Ecology and Genomics, Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria 0002, South Africa
2. Rhizosphere Processes Group, Swiss Federal Research Institute WSL, 8903 Birmensdorf, Switzerland
3. Departments of Geology and Geography, Portland State University, Portland, OR 97212, USA
4. Department of Environmental Science, iClimate, Aarhus University, DK-4000 Roskilde, Denmark