Variation of Soil Bacterial Communities Across a Vegetative Transect of Live Oak and Ashe Juniper.

Soil microorganisms drive biogeochemical cycling and soil microbial communities differ based on pH, soil moisture, texture, organic carbon, and available nutrients. In Texas, Ashe juniper (Juniperus ashei) is encroaching on live oak (Quercus virginiana) savannas, which may alter the soil microbial communities and therefore the ability of the soil ecosystem to cycle nutrients. The objective was to determine whether soil microbial communities differ under the canopies of Ashe juniper and live oak. We hypothesized that groups of Ashe juniper have different community composition than lives oaks and differ from open grasslands in the same soil. We identified 3 transects of live oak, Ashe juniper, and grasses. At each transect we collected 4 samples from the A horizon in 4 areas: under the live oak canopy, under the overlapping canopies of live oak and Ashe juniper, under the Ashe juniper canopy, and in grasses away from the trees. We characterized soils by pH, texture, calcium carbonate equivalence, total nitrogen, and total carbon. Microbial communities were analyzed using massively parallel DNA sequencing, and separated into Operation Taxonomic Units (OTUs) based on 97% sequence similarity. We analyzed results through Qiime using PERMANOVA, Mann-Whitney U, and Spearman’s rank correlations. Preliminary results show microbial communities of oak and overlapping oak and juniper are similar to one another, while juniper communities are similar to native grass communities. Nitrogen cyclers (Nitrospirae and Candidatus Nitrososphaera) were among the microbes that varied across sites. We suggest that despite differences in microbial communities across sites, there are distinct differences associated with vegetation. Community changes across sites could impact nitrogen cycling.