PARENT SESSION
Organized Oral Session 48: Nitrogen cycling in terrestrial ecosystems: New insights from isotopes and experiments
Organizer(s): MC Mack, P Templer, and K Nadelhoffer
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 510b, Level 5, Palais des congrès de Montréal

The changing nitrogen cycle in alpine tundra: Results from ¹⁵N tracer experiments.

Holland, Keri^*,1, Townsend, Alan¹, Bowman, William¹, Seastedt, Tim¹, ¹ University of Colorado, Boulder, Boulder, CO, 80302

ABSTRACT- Alpine tundra ecosystems in Colorado are experiencing increasing rates of nitrogen (N) deposition. A number of ecosystem changes are evident at rates of N fertilization likely to occur within the next century. Experimental N fertilization in alpine tundra can alter plant community composition, increase aboveground productivity, increase inorganic N pools in soil, and alter microbial functional capabilities. These changes are hypothesized to alter pathways for N retention in and loss from alpine tundra. For example, changes in plant community could accelerate N loss via changes in litter quality. In contrast, changes in microbial functional capability could slow rates of decomposition and facilitate greater N retention. In this talk, we will synthesize key results from three ongoing ¹⁵N tracer experiments with the aim of understanding how the partitioning and retention of N in alpine tundra changes across a range of N fertilization levels and in drought versus more normal moisture years. Specifically, we will highlight key differences in the initial partitioning of N within the ecosystem and discuss how these differences could alter longer-term N retention. For instance, data show plants are a rapid and significant sink for N inputs even at levels well above current rates of N deposition. Finally, we will discuss the similarities and differences of these results to other ecosystem ¹⁵N tracer experiments using meta-analysis data, in order to lend insight into why the consequences of N fertilization in alpine tundra ecosystems could differ from other ecosystem types.

Key words: Carex rupestris, critical load, nitrogen deposition, precipitation