||A refined understanding of how microbial processing of organic C responds to expected climate changes is needed to improve our fundamental understanding of the soil C cycle and its representation in C biogeochemical models. Our 2012 work has focused on a lab incubation of soil cores from the Arid Lands Ecology Reserve (Richland, WA), which was the location of a soil transplant experiment in 1994; soils were transplanted between the cooler, moister upper slope location (844 m) and the hotter, dryer lower slope location (310 m). The upper-mountain site is ~6° cooler and receives ~9 cm more precipitation annually than the lower site. We resampled sub-cores from these transplant soils and incubated them for 100 days in two environmental chambers programmed to simulate the climate at both locations to study the decadal consequences of climate change on soil C biogeochemistry and resilience as inferred from a defined set of chemical and physical assays. Our hypotheses (presented in full in the original proposal) included: 1) altered soil biogeochemistry will shift microbial communities, 2) the shift from cooler, moister to hotter and drier conditions will more rapidly destabilize soil C and alter the microbial community structure and function than will the reverse change, and 3) soils returned to a simulation of their original climate conditions 17 years after transplanting to a different elevation (an abrupt climate change) will have converged with the soils adjacent to their new elevation and thus, will respond similarly to these adjacent native soils. Our results show that soils that underwent two climate change events in the past 17 years (i.e., on-mountain transplant in 1994, followed by return to their original climate in the 2012 lab simulation) were significantly altered compared with soils that had only experienced a single climate change (i.e., either the 1994 transplant, or a single simulated transplant in the lab). The soil cores that experienced the two climate change events had Q10 values of ~1, indicating that biological processes were unable to respond to temperature. In contrast, the other soils had Q10 values of ~2.3. Additionally, the remaining soil cores (those only subjected to a single climate change event, whether as a 1994 transplant or in the lab incubation in 2012) had the greatest loss of C via respiration when incubated under the hotter drier climate simulation, yet these same samples had significantly lower potential β-glucosidase and N-acetylglucosaminidase activities. Thus, internal cycling of C was slower under the stress of the hotter drier condition, yet C losses were much greater. Finally, ribosomal intergenic spacer analyses revealed that microbial communities in soils originating from a particular 1994 location retain similarities, even after nearly 2 decades at disparate elevations. The data collected in the climate simulation incubation are being used to stringently test the ability of a typical CLM-style biogeochemical model, such as Biome-BGC, to predict observed phenomena occurring under changing conditions. Such models typically assume relatively invariant Q10 values of ~2, and as such, would not be able to replicate our findings for these soils. In parallel work, the characterization of the soil cores used in this experiment is being used to establish a virtual core model for evaluation of biogeochemical process models at both pore and core scales, and for development of mechanism-based biogeochemical process models to be included into reaction-based CLM.