Diversity Down below: Does Fertility Impact the Rhizosphere Microbial Community in Poa Annua Turf?.

Nitrogen (N) and potassium (K) are essential for maintaining healthy turfgrass, but little is known about whether these nutrients affect microorganisms in the rhizosphere. The objectives of this study were to evaluate the composition, diversity, and distribution of beneficial and pathogenic microorganisms in the rhizosphere of Poa annua turf treated with nitrogen (N) and potassium (K). Three 16 mm x 51 mm soil cores were sampled from four replicated plots receiving: 100, 132, or 200 kg N ha^-1 yr^-1; 200 kg K₂O ha^-1 yr^-1; or 132 kg N ha^-1 yr^-1 and 200 kg K₂O ha^-1 yr^-1. N was applied as urea [CO(NH₂)₂] and K as KCl. Organism-specific DNA regions were PCR amplified from fungi (Internal transcribed spacer 1 and 2), bacteria and archaea (16s).  Multiplexed next-generation Illumina sequencing generated 2.3 x 10⁷ paired-end reads (avg. 1.38 x 10⁵ seqs/sample; 253 bp average read length). The QIIME (Quantitative Inisghts Into Microbial Ecology) pipeline picked 8.3 x 10⁵ OTUs, 4.1% of which were identified as archaea, 26.7% bacteria, and 29.7% fungi. Alpha diversity metrics showed that microbial diversity was highest in low and high N treatments, while diversity was lowest in plots receiving the intermediate rate of N . Detrended correspondence analysis plots and Kruskal–Wallis ANOVAs revealed differences in microbial community structure across all treatments, particularly amongst archaea and bacteria from plots receiving intermediate N, K, or intermediate N+K treatments, compared to those receiving low or high rates of N . A similar finding was observed for the fungal community, indicating that N and K treatments can affect the composition and structure of rhizosphere microbial communities in P. annua turf, and that this environment is very diverse and species-rich.