library_construction_protocol: "The DNA extraction was performed with the FastDNA Spin Kit for Soil (MP Bio, USA) according to manufacturer’s instructions. Primers 515 forward 5’-GTGYCAGCMGCNGCGG-3’ and 926 reverse 5’-CCGYCAATTYMTTTRAGTTT-3’ (adapted from Walters et al. (2016) while modifying the forward primer) were utilized to target hypervariable regions V4–V5 of the 16S rRNA genes amplified by PCR in a final volume of 15 µL with: KAPA HiFi HotStart ReadyMix (Kapa Biosystems, Boston, MA, USA) containing 0.02 U/µL of KAPA HiFi HotStart DNA Polymerase, 2.5 mM MgCl2 and 0.3 mM of each dNTP; 0.3 µM of each primer (Generi Biotech, Czech Republic); template DNA (~20 ng). The cycling program was set as follows: 5 min at 95 °C, 20 cycles of 20 s at 98 °C, 15 s at 56 °C, 15 s at 72 °C and a final extension of 5 min at 72 °C. A volume of 0.5 µL of the PCR product was utilized as template for another round of PCR, performed under the same conditions, except that the final reaction volume was 25 µL, with 1 µM of each primer, and the cycle number was decreased to 5-10. The forward and reverse primers utilized for the second PCR were modified with sequencing adapters for Illumina sequencing systems . The resultant PCR products were purified using AMPure XP Beads (Agencourt, Beckman Coulter, USA) and were further indexed and sequenced on a MiSeq sequencing system at the University of Alaska Fairbanks core facility."