Effects of Nitrogen Fertilization on Plant Communities of Nonsorted Circles in Moist Nonacidic Tundra, Northern Alaska

Nitrogen availability is considered to be a key limiting factor for plant growth in arctic tundra. Freeze-thaw cycles, which can produce patterned-ground features, may also limit the establishment and growth of arctic plants. In this experiment, we fertilized nonsorted circles, a type of patterned-ground feature, and the surrounding more stable vegetation in moist nonacidic tundra of northern Alaska to determine if nitrogen availability limited plant communities on these disturbance-dominated features. Similar to other studies in moist nonacidic tundra, the fertilized stable vegetation showed an increase in graminoid biomass and a decrease in moss biomass, but no total biomass response. The plant communities on nonsorted circles were less responsive to the addition of nitrogen as compared to the well-vegetated rims. The nonsorted circle vegetation may be limited by additional factors, such as frost heave disturbance, availability of buried seeds, and/or other nutrients. This difference in fertilization response shows that the presence of these features creates spatial heterogeneity in tundra plant community dynamics that should be taken into account when studying tundra responses to environmental change.