Climate change is expected to alter important process operating in soil ecosystems such as microbial activity, biogeochemical cycling, and hydrological processes, and thus soil functioning and the delivery of a range of ecosystem services. Under future climate change scenarios, extreme weather events are predicted to become ever more frequent globally, with rising temperatures and concentrated rainfall events having an impact on soil functioning. It is necessary to study how changes in soil moisture status and/or temperature will affect soil respiration for predicting future changes in soil carbon (C) storage. In the scientific literature, previous studies have frequently observed a CO2 pulse from soil after a freeze-thaw or dry-wet event; however, the mechanisms underlying these effects are not well understood. The first experiment of this thesis (Chapter 3) investigated how a single freeze-thaw or dry-wet event affected microbial C dynamics using 14C tracking. Our results revealed that freeze-thaw or dry-wet events altered the allocation of C into labile and structural microbial C pools. The next experiment (Chapter 4) investigated how the C budget of an intact plant-soil system responded to freeze-thaw and dry-wet events. The presence of plants resulted in significantly greater total CO2 flux following freeze-thaw or dry-wet events in comparison to the unplanted soil. The greater CO2 efflux seen after thawing or rewetting was caused by a disruption of the microbial biomass, rather than a stimulation of soil organic matter turnover (Chapter 5). This was supported by a decrease in extracellular enzyme activity immediately after freeze-thaw or dry-wet event (Chapter 5). We also showed that soil microbes accumulated osmotic solutes (i.e. sugars and polyols) in response to extreme freeze-thaw or dry-wet events. In this thesis, the microbial community quickly responded to freezing or drying events by altering cellular metabolism (Chapter 6). The final experimental chapter (Chapter 7) investigated how future climate scenarios may affect arctic ecosystems. We monitored greenhouse gas (GHG) emissions and nutrients in soil solution throughout a year in response to a 2050 and 2100 climate warming scenario. A simulated warmer winter led to enhanced microbial decomposition of soil organic matter with increased CO2 efflux and more N becoming available to roots and associated mycorrhiza in the Arctic soils. We hypothesize that this could lead to a potential future shift in plant communities. In conclusion, this thesis present events showing that under future climate scenarios, an increase in freezethaw or dry-wet events will alter soil C and N processing in soils and disrupt biogeochemical cycling. We also conclude that the presence of plants is key in determining how ecosystems respond to these extreme events.