Although the fate of carbon stored in soil is central to the global climate trajectory, many essential parameters describing the microbial-mediated processing of this carbon are poorly defined. For instance, soil carbon projections are highly sensitive to assumptions about microbial carbon use efficiency - or the fraction of carbon taken up by a cell that is incorporated into biomass - yet we lack a mechanistic understanding of the microbial response to changing abiotic conditions. The objective of the present research is to evaluate the diversity of responses that bacterial carbon use efficiency shows to changing abiotic conditions. Using diverse soil bacteria isolated from the Harvard Forest, we found that the temperature sensitivity of carbon use efficiency varies in a substrate- and isolate-specific manner. Ongoing work is evaluating how soil carbon projections change with warming under different microbial carbon use efficiency "cliques", and offers an opportunity to link cellular physiology at the microscale to community level processes at the meter scale.