16S rRNA V4 amplicons sequenced from switchgrass rhizosphere soil samples collected from LTER mesocosms. DNA extracted using DNeasy PowerSoil kit. Fractionated by CsCl density gradient to separate heavy/light DNA fractions. Individual fractions and unfractionated pools were amplified with universal 515F/806R primers modified as per Illumina protocol, and pooled for paired-end Illumina MiSeq sequencing (2x250bp).