Increasing levels of nitrogen (N) deposition have been identified as critical concerns for ecosystems worldwide. High-elevation plant communities are generally adapted to low soil resource supply and increases in N may result in significant changes in biomass and species composition.  Understanding the effects of N deposition on alpine plant and soil communities is needed for the development of “critical loads” to inform and improve air quality policy and protect high-elevation ecosystems, and there has been relatively little research on the effects of N deposition on alpine plant and soil communties of the PNW. This project uses 15N fertilization of plant communities in the alpine of three PNW National Parks (Mount Rainier, North Cascades, and Olympic) to document effects on plant and soil community dynamics and to derive initial estimates of N critical loads for these alpine systems. We will present data on nitrogen storage, C/N ratios, and 15N/14N ratios of soils and plant and root tissues in these three plant communities, as well as immobilization/mineralization of N by alpine microbial soil communities.