Bacterial Biogeography of the rare Charitable Research Reserve.

Microbial communities play a dominant role in global biogeochemical cycles, with profound effects on agriculture, ecosystem stability, human health, and global climate. Due to extensive spatial heterogeneity and environmental gradients, there is potential for overlooking critical metabolic processes and novel bacterial taxa within deeper soil horizons that can be highly dependent on changes in land-usage. The objectives of this study were to examine depth-dependent bacterial community changes across multiple land-use types, as well as probe for novel and low-abundance bacterial taxa. We collected soil samples across seven distinct land-use types to depths of 45 cm, including old-growth and mature forests, decommissioned, and active agricultural fields from the rare Charitable Research Reserve (Cambridge, Ontario). Bacterial communities were characterized by sequencing of bacterial 16S rRNA gene amplicons coupled with multivariate statistical analyses. Soil bacterial communities across all sites were strongly influenced by depth, land-use type, and pH. Alpha diversity was typically highest in upper soil profiles (0–15 cm) and decreased significantly with depth. Soils from open fields showed higher alpha diversity relative to forested sites. Maximum alpha diversity was observed for neutral to near-neutral pH soil samples. These diversity differences likely reflect the importance of edaphic factors and site disturbance in shaping soil microbial communities. Soils across all sites and depths were dominated by Alphaproteobacteria, Deltaproteobacteria, and Acidobacteria members. Recovered indicator species were strongly linked to pH and land-usage, with observable community differences between field and forested sites. Variations in pH across all sites, and with depth, was a critical physicochemical parameter correlating strongly with overall community composition. These results exemplify important global environmental gradients including depth, land-usage, and soil biogeochemistry operating at smaller geographical scales across consistent underlying geology. Ongoing work is aimed at surveying these soil profiles for novel, low-abundance bacterial taxa to assess their biogeography and ecological role.