Reduced vertical stratification of soil bacterial community structure and composition is associated with Bromus tectorum invasion of sagebrush steppe

Sagebrush steppe (Artemisia tridentata and congenerics), one of the most extensive ecotypes in the Western United States, is being decimated by the invasion of a nonnative annual, Bromus tectorum (cheatgrass). Sagebrush loss negatively impacts the distribution of macrofauna, but the impact on soil microbial community structure and composition remains unresolved. High-throughput amplicon sequencing (16S rDNA) was conducted on two soil depth intervals (0-4 cm (T) and 4-8 cm (B)) in 12 spatially separated soil cores collected from cheatgrass (C)- or sagebrush (S)-dominated soils to determine how soil microbial communities associated with cheatgrass and sagebrush may differ. Average normalized bacterial richness was significantly lower in SB libraries than in the ST, CT or CB libraries. Soil depth impacted diversity indices only in S soils with Chao1 and Shannon diversity indices being significantly lower in SB than in ST libraries. Non-metric multidimensional scaling plots indicated that the community composition of SB soils was distinct from the others examined; shifts along axes were most highly correlated with Acidobacteria, Bacteroidetes, Armatimonadetes, unclassified Archaea, Crenarcheota and Firmicutes. These findings demonstrate that the vertical stratification of soil bacterial community structure and composition is reduced in association with cheatgrass relative to that in association with sagebrush.