design: Total microbial genomic DNA was extracted from samples using the FastDNA SPIN Kit for Soil, qualitychecked by 1% agarose gel and NanoDrop2000, the 454F-V4R region of 18S rRNA was PCRamplified with primers 454F(5-CCAGCASCYGCGGTAATTCC-3)/V4R(5-ACTTTCGTTCTTGATYRA-3) using Fast Pfu polymerase (95  3 min; 27[95  30 s, 55  30 s, 72  45 s]; 72  10 min), purified from 2% agarose gel, quantified by Qubit 4.0, pooled equimolarly, and pairedend sequenced on an Illumina Nextseq2000.