Invasion of exotic species threatens the stability of ecosystems and is regarded as a significant component of global ecological change. One of the most successful invasive species of the intermountain west of the United States is Bromus tectorum L. (downy brome)—an annual Eurasian grass that was first observed in North America in the late 1800s in areas of Washington, Oregon and Utah and now covers ca. 40,000,000 ha. The prevalence of B. tectorum raises concerns regarding its potential effects on ecosystem structure and function. In this study we investigated the effects of invasion of B. tectorum on an ungrazed grassland in Canyonlands National Park, Utah. Because the invasion occurred on previously established study transects, we were able to assess the short-term effects of an invasion with a known entry date. We conducted long-term soil incubations in the laboratory to obtain data on cumulative nitrogen mineralization which was used to calculate the size of the labile pool of soil nitrogen. We also measured in situ soil inorganic nitrogen and net nitrogen mineralization. We found that, 2 y following the invasion of B. tectorum, the labile pool of soil nitrogen was 50% smaller for invaded sites compared to uninvaded sites. In addition, invaded sites had significantly reduced in situ inorganic nitrogen and net nitrogen mineralization compared to uninvaded sites. The mechanisms for these changes in soil nitrogen cycling and nitrogen availability may be related to differences in the phenology, litter composition and biomass of B. tectorum compared to native grass species. These findings suggest availability of key resources is dramatically influenced by invasion of B. tectorum at these sites.