16S and ITS sequencing of  Populus microbiome
A two-step PCR approach was used with barcode tagged and frameshifting nucleotide primers targeting the 16S rRNA gene for archaea & bacteria and the ITS2 region for fungi (Lundberg et al. 2013) with modifications to primers, PNA blocker oligos, and PCR conditions described previously (Cregger et al. 2018). After PCRs, all experimental units were pooled based on band intensity and purified with Agencourt AMPure XP beads (0.7:1 bead to DNA ratio; Beckman Coulter Inc., Pasadena, CA, USA). Illumina MiSeq sequencing was carried out using a 9 pM amplicon concentration with a 15% PhiX spike (2x300 cycles).