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Productivity-diversity theory has proven informative to many investigations seeking to understand drivers of spatial patterns in biotic communities and relationships between resource availability and community structure documented for a wide variety of taxa. For soil bacteria, availability of organic matter is one such resource known to influence diversity and community structure. Here we describe the influence of environmental gradients on soil bacterial communities of the McMurdo Dry Valleys, Antarctica, a model ecosystem that hosts simple, microbially-dominated foodwebs believed to be primarily structured by abiotic drivers such as water, organic matter, pH, and electrical conductivity. We sampled 48 locations exhibiting orders of magnitude ranges in primary production and soil geochemistry (pH and electrical conductivity) over local and regional scales. Our findings show that environmental gradients imposed by cryptogam productivity and regional variation in geochemistry influence the diversity and structure of soil bacterial communities. Responses of soil bacterial richness to carbon content illustrate a productivity-diversity relationship, while bacterial community structure primarily responds to soil pH and electrical conductivity. This diversity response to resource availability and a community structure response to environmental severity suggests a need for careful consideration of how microbial communities and associated functions may respond to shifting environmental conditions resulting from human activity and climate variability.