Climate change is affecting many temperate forest ecosystems globally, yet a mechanistic understanding of how climate factors affect microbially-mediated soil processes, including fluxes of the major greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), remains limited. Alteration to precipitation patterns, including the intensity, duration, frequency, and timing, of high rainfall events, are expected to modify forest soil moisture dynamics over the forthcoming century, alongside simultaneous changes in atmospheric CO2 levels which are predicted to reach 550 ppm by 2050. Here, we used both observational (natural extreme weather events) and experimental (field and laboratory climate manipulations) approaches to determine how altered precipitation and elevated atmospheric CO2 concentrations impact soil microbial community structure and function within organic and mineral soil horizons, and within tree fine roots. We integrated genomic and biogeochemical methods and utilised two field sites to answer our research questions: (i) a willow (Salix viminalis) bioenergy plantation forest, and (ii) a unique atmospheric CO2 enrichment facility, the only such site in the world located within a mature temperate deciduous oak-dominated (Quercus robur) forest, to characterise effects on forest soil GHG and nutrient cycling. Overall, our results showed that increased precipitation reduced soil respiration and soil CH4 sink capacity, whilst soil N2O emissions were unaffected. Interactions between precipitation and atmospheric CO2 concentration affected the magnitude of the response, and the length of the recovery, of the net soil GHG fluxes. Soil extracellular enzymes, involved in C, N, P and S cycling, were affected by precipitation and atmospheric CO2 levels by varying magnitudes according to enzyme function. We determined that bacterial and archaeal community composition and diversity were relatively stable to periods of high precipitation, but extreme precipitation, associated with prolonged soil saturation, altered root-associated microbial community structure, including the relative abundance of methanogenic archaea. Together, the results presented in this thesis has begun to unravel how temperate forest soils will respond to future climate scenarios.