Soils hold more carbon (C) than the atmosphere and vegetation combined. This pool of C may be a source or a sink to the atmosphere depending on the microbial mediators of detrital decomposition. However, we are just beginning to discover the identities and ecological functions of the vast majority of uncultivated soil taxa. Edaphic variables like soil pH often govern microbial community composition. In this dissertation, I explore how manipulating soil pH through liming affects microbial community composition and decomposition in acidic northern hardwood forest soils. In Chapter 1, I investigate changes in decomposition and bacterial and fungal community composition in limed forested subcatchments where soil C stocks had accumulated over two decades. Liming altered bacterial and fungal composition, decreasing the relative abundance of ectomycorrhizal and saprotrophic fungi as well as actinomycetes that were correlated with lignocellulolytic enzyme activity. In Chapter 2, I compare liming-induced shifts in bacterial and fungal community structure and activity between a short- and long-term liming experiment in northern hardwood forests of the Adirondacks to elucidate the role of pH. Within two years of liming a majority of taxa responded similarly to the long-term site. Connecting microbial structure and function directly through stable isotope probing in Chapter 3, I prove that limed bacterial and fungal communities metabolize leaf litter C differently than in control acidic soils. This dissertation bridges scales ranging from ecosystem processes to individual microbial taxon function, connecting the structure of microbial communities to their function in ecosystem C-cycling. The impact of climate change, the most urgent problem of the Anthropocene, will depend heavily on understanding the responses of soil microorganisms.