Background/Question/Methods High-elevation ecosystems that are above the zone of continuous vegetation and below the zone of permanent ice and snow consist of largely unvegetated expanses of soil that have received little study. Such areas are highly sensitive to global change, as glacial retreat and changes in snow cover and extent are affected by global warming. Furthermore, research has shown that eolian deposition is a primary driver of biogeochemical cycling in these areas and therefore eolian inputs from adjacent ecosystems, both natural and anthropogenic, impact local biogeochemistry. Less understood are the roles of microbes in the absence of plants and how microbial community composition and activity may contribute to carbon and nutrient cycling in these remote areas. In this study we focus on high-elevation, unvegetated soils (i.e. >3500 m above sea level) in the Green Lakes Valley, Colorado Front Range. This watershed receives 5-7 kg/ha/yr of N deposition and is a regionally significant source of drinking water. We investigated the microbial community composition across the three domains of life, at two soil depths, among three sites. Furthermore, we investigated seasonal changes in bacterial communities, the functional gene ammonia monooxygenase (AMO), and relevant biogeochemical parameters. Results/Conclusions We determined that a diverse microbial community is present and actively fixing and respiring carbon. Soil CO₂ flux data indicate that light-driven CO₂ uptake occurred on most dates during the snow-free period. We found a number of photoautotrophic bacteria and microscopic green algae in our clone libraries, likely responsible for the observed CO₂ uptake. While eolian deposition of carbon was determined to be of less importance than that of CO₂ fixation, we found that pollen deposition may be a significant carbon source for this ecosystem. Fungal libraries were dominated by chytrids further indicating the importance of exogenous pollen inputs to this system. Chemoautotrophs also appear to contribute to CO₂ uptake in the soil and nitrification by such organisms has been suggested to dramatically impact NO₃- levels in the watershed. While known nitrifiers were not obvious in our clone libraries, we determined the diversity and seasonality of bacterial and archaeal nitrifiers via seasonal measurement of AMO genes and inorganic nitrogen fluxes. We found that bacterial and archaeal AMO are present and diverse in the soil and that AMO abundance varies throughout the snow-free period, as does the abundance of NH₄+ and NO₃-.