Environmental Drivers of Dissimilarities in Soil Microbial Communities in Sagebrush Steppe Ecosystems

Soil microbial communities play a key role in ecosystem function, plant nutrition, and plant population dynamics. The composition of these microbial communities can vary greatly across geographic regions and climatic conditions, even at small spatial scales. Many studies have explored the effects of environmental factors on soil microbial composition, however, few studies have examined the drivers of bacterial community structure in arid ecosystems. In this study, we investigated how soil properties and climate variables correlated with the composition of sagebrush steppe soil bacterial communities. We collected soils from sagebrush stands that spanned gradients in climate and soil properties and extracted DNA for amplicon sequencing targeting the 16S region of the small ribosomal subunit. We then constructed generalized linear mixed models informed by a directed acyclic graph to examine the effects of climate (e.g., precipitation and temperature) and soil (e.g., pH, nitrogen, and organic matter) properties on the Bray-Curtis distances between microbial communities. We compared soils across sites and within sites, from rhizosphere and shrub interspace samples. Contrary to previous studies, we found that both soil nitrogen and pH had weak (but significant) effects on dissimilarities in sagebrush steppe bacterial communities. Instead, we found that mean annual precipitation and mean annual temperature had the strongest correlations with bacterial community dissimilarity after accounting for other site-level factors. Soil bacterial communities differed between rhizosphere and interspace samples; however, these within-site dissimilarities were smaller than across site comparisons, and none of the measured soil abiotic properties were strongly correlated with bacterial dissimilarities. This finding suggests that other biotic factors, such as the shading or hydrological impacts from sagebrush shrubs may better explain differences between rhizosphere and interspace communities. The results of our study indicate that soil bacterial communities in sagebrush steppe are strongly correlated with large scale climate factors such as temperature and precipitation as opposed to soil factors such as soil pH. Given the impacts of soil microbes on ecosystem function and plant population dynamics, understanding the climate and soil-related drivers of bacterial community composition may help us understand anthropogenic impacts on ecosystems, including land use change, climate change, and species invasions