Background/Question/Methods
One of the fundamental questions in microbial ecology is whether communities that differ in composition also differ in function.  Emerging molecular tools have greatly improved our ability to define and measure microbial community composition, but progress in defining and measuring specific functions has been slower.  Due to the difficulties in assessing the relationship between phylogeny and function, we have little understanding of the roles of microbial community composition in responses to global change. 
In the Rocky Mountains of the western US, a recent pine beetle epidemic has caused rapid death of vast swaths of pine forest. The future composition of replacement stands is unknown, but it is likely that much of the forest will be replaced by other species such as Aspen.  As Aspen stands establish in soil that had previously hosted Pine stands, will those microbial communities function in the same way as longer established Aspen stands?  Specifically, we tested whether Aspen leaf litter is decomposed at the same rate, and by the same metabolic pathways in adjacent Aspen, Engelmann spruce, and Lodgepole stands.  We used a molecular community fingerprint technique to examine whether the decomposer communities differed in structure, and analyzed the soluble metabolic products following one year of decomposition using a high resolution mass spectrometry approach (UPLC-Q-TOF).  Our hypothesis was that microbial community composition would differ under each forest type, and that each community would decompose Aspen litter by different metabolic pathways.
Results/Conclusions

We found that the community structure in the organic soils differed by forest stand type based on a NMS analysis of community fingerprints (T-RFLP).  The soluble metabolic products of Aspen litter decomposition also differed between forest stands, based on a partial least squares-discrminant analysis (PLS-DA) of features identified by UPLC-Q-TOF.  This data suggests that microbial communities that differ in composition also differ in function.  Specifically, we found that these communities decomposed a common litter by alternate metabolic pathways.  The unique chemical fate of the Aspen litter in each forest stand has important implications for long-term soil organic matter dynamics and C balance.