PCR using barcoded Illumina primers was performed by following the Earth Microbiome protocols (Caporaso et al. 2012), with the following differences: HF Phusion polymerase mix (New England BioLabs, Ipswich, MA) was used and 3% dimethylsulfoxide (DMSO) was added to the reaction mixtures before cycling at 98????????????????????????????????C for 45 s, 50????????????????????????????????C for 60 s, and 72????????????????????????????????C for 90 s.  Amplifications for each sample were performed in triplicate and pooled befor normalization based on Quant-iT PicoGreen dsDNA Assay Kit DNA quantification.