Background/Question/Methods Changes in both temperature and the amount and timing of precipitation have the potential to profoundly impact the soil environment during winter and spring with resultant changes in biogeochemical cycles.  Recent years have seen a growing number of research projects focused on quantifying how variability in winter climate affects biogeochemical cycling, and how cold season processes affect annual biogeochemical fluxes.  This presentation reviews work over the last two decades on the interactions between seasonal snow cover, soil physico-chemical characteristics, biological activity, and plot- to ecosystem-scale carbon and nitrogen fluxes in montane ecosystems.

Results/Conclusions A consistent theme that has emerged from these studies is the importance of the timing and amount of liquid water available both to microbes and vegetation in controlling the magnitude of in situ activity and both gaseous and dissolved biogeochemical fluxes.  At temperatures near and below 0^oC that characterize subnivean soils, water can be present as a liquid, solid, and gas simultaneously, with phase transitions strongly buffering soil temperature.  Consequently, highly variable temperature responses (Q10’s) in subnivian soils result from changes in available liquid water and dissolved substrates, in addition to direct effects on reaction kinetics.  Unfortunately, both liquid water and temperature are difficult to measure accurately within the range of conditions within subnivian soils, complicating efforts to predict winter biogeochemical response to climate change.  However, observations of both microbial and vegetation processes identify critical thresholds that appear to control the magnitude of biogeochemical fluxes.  Interpreting these threshold-type responses from an energy balance perspective that includes water phase transitions provide inferences that are consistent with growing season observations.