Under predictive climate change models, species’ ranges are expected to move poleward in latitude and upward in elevation with warming. As tree species move upslope, the leaf litter produced may present a novel litter source to the present microbial community. Given the possibility that biogeographic patterns in microbial communities may translate to dissimilarity in microbial community function, novel litters may be perceived differently to what would be expected based on their chemical and physical composition. As such, the role of a specific litter type in the biogeochemical cycle of its current environment may not be a good predictor of its role in a new, higher-elevation environment. As a low elevation, “high” litter quality species moves out of its current habitat into areas of more recalcitrant litter and lower mineralization rates, system C and N dynamics may change in yet undetermined ways. We examined how soil microbial community function, examined as carbon fluxes from decomposing leaf litters, responds to a shift in dominant, overstory tree species across an elevation gradient. We used a common garden, laboratory microcosm design (soil community inoculum x litter environment) with single and mixed-species litter environments. Microcosm CO₂ efflux was measured across 300 days.

Results/Conclusions

The three soil inocula represent an elevation gradient ranging from 795 m to 1634 m. The four litters represent the dominant tree species at each elevation plus a ubiquitously-dispersed control. Within each single-species litter environment, we found a negative relationship between cumulative CO₂-C and elevation (represented by soil inocula). This indicates that the inocula are functionally distinct. Additionally, soil inocula sourced from field litter sources exhibited ‘home-field advantage’, where inoculum paired with its native tree species litter (e.g. low-elevation litter species plus the low elevation inoculum) had the greatest cumulative CO₂-C values. “Home-field advantage” was also evident in the microcosms involving mixed-species litter environments. This suggests that soil microbial community function is dependent on resource history. In the mixed-species litter environments, we found both positive and negative interactions on cumulative CO₂-C. Greater than expected cumulative CO₂-C values were generally found in litter mixtures involving the fourth, ubiquitously-dispersed litter type. However, there were a higher percentage of negative interactions suggesting a negative influence of more recalcitrant litter types on those of higher quality. Our results suggest that tree species identity and species composition influence soil microbial community function across an elevation gradient.