The Balance of Coexistence in Alpine Tundra

We are exploring how feedbacks between plant species and ecosystem processes can enhance community diversity and stability in moist meadow alpine tundra. In this system, two functionally different plant species are able to coexist due to their impacts on nitrogen cycling: net N mineralization and nitrification rates are four times greater in areas dominated by Deschampsia caespitosa than areas dominated by Acomastylis rossii. This species-driven variation occurs within meters and is as great as the variability across different communities in the tundra. Deschampsia, directly through rapid N uptake, and Acomastylis, indirectly through microbial N immobilization of its litter, exert strong and often equivalent competitive effects (Suding et al. 2004; Suding et al. 2006).

Because we anticipate that many alpine species exert strong feedbacks through the soil microbial community, we are initiating an investigation of a broader range of species, specifically focusing on species effects on microbial processes and whether these effects are related to N-form preferences (inorganic, organic N) of the species and their competitors. Plant utilization of different forms of nitrogen and litter inputs of secondary carbon compounds can substantially influence community and ecosystem dynamics. While both are driven by N availability and microbial processes, they rarely have been considered as joint factors contributing to strong biotic feedbacks . We are exploring these linkages to understand when plant species create such feedbacks, how these contribute to diversity patterns, and how abiotic and biotic control varies across the alpine tundra.


 We are also investigating how increased nitrogen availability from atmospheric deposition may shift species interactions and ecosystem processes, particularly in the presence of strong plant-soil feedbacks. This work is based at Niwot Ridge as part of the Long-term Ecological Research (LTER) project. At larger scales, I lead a synthesis effort across nine LTER sites to investigate functional responses to nitrogen inputs across many ecosystems in temperate North America (Suding et al. 2005; Pennings et al. 2005; Clark et al. 2007)

Collaborators: Scott Collins (UNM), Steve Pennings (UH), Chris Clark (UMinn), Elsa Cleland (NCEAS), Laura Gough (UTA), Jim Grace (USGS), Joe Fargione (UNM), Kay Gross (MSU), Daniel Milchunas (CSU). Funded by Niwot Ridge LTER and LTER Network Office.