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
All materials copyright The Ecological Society of America (ESA), and may not be used without written permission.