1. CNRS, Aix-Marseille Univ., IRD, INRAE, CEREGE, 13545 Aix-en-Provence, France
2. Laboratory of Microbial Ecology of the Rhizosphere, Aix Marseille Univ, CEA, CNRS, BIAM, LEMiRE, ECCOREV FR 3098, F-13108 Saint Paul-Lez-Durance, France
3. Civil and Environmental Engineering Department, Duke University, Durham, North Carolina 27707, United States