16S rRNA gene sequencing: soil samples
MoBio powersoil DNA extraction;  DNA from each sample was amplified using 16S rRNA primers: 341F (5Õ-AATGATACGGCGACCACCGAGATCTACACTA-TGGTAATTGTCCTACGGGAGGCAGCAG-3Õ) and reverse 806R (5Õ-CAAGCAGAAGACG-GCATACGAGATNNNNNNNNNNNNAGTCAGTCAGCCGGACTACHVGGGTWTCTAAT-3Õ). The PCR amplicons were quantified by PicoGreen (Invitrogen, Carlsbad, CA) using a plate reader.  After quantification, amplicons were pooled in equal concentrations and the pool was cleaned up using UltraClean PCR Clean-Up Kit (MoBio, Carlsbad, CA). The pooled samples were sequenced on a MiSeq Illumina sequencer according to the sequencing procedures described in Caporaso et al. (Caporaso et al., 2012).