Positive Feedbacks to Anthropogenic Nitrogen Deposition in Rocky Mountain Alpine Tundra

Bowman, William; Steltzer, Heidemarie

Increasing deposition of anthropogenic N may detrimentally impact terrestrial and aquatic ecosystems. Research on the impacts of N deposition has focused primarily on regions with rates > 10 kg N ha-1 yr-1, yet lower rates may substantially impact ecosystems with lower biological capacity to sequester the additional inputs of N. Alpine tundra, due to low rates of primary production and soil microbial activity, is susceptible to biotic impacts resulting from high N deposition. Increases in N availability in alpine tundra of the southern Rocky Mountains, which is experiencing elevated rates of N deposition from anthropogenic sources (8-10 kg N ha-1 yr-1), will lead to changes in plant species composition as a result of competitive displacement. Such changes in plant community structure will have positive feedbacks to rates of N cycling. In moist meadow communities, replacement of the dominant Acomastylis rossii by Deschampsia caespitosa will lead to an eightfold increase in net N mineralization and nitrification rates, which in turn will increase groundwater loss of NO3 - to aquatic ecosystems.

Positive Feedbacks to Anthropogenic Nitrogen Deposition in Rocky Mountain Alpine Tundra

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