PARENT SESSION
Symposium #8: Nitrogen deposition in the Western U.S.... Is there cause for concern?.
Sponsored by ESA Rocky Mountain Chapter
Organized by: H.M. Rueth and J.S. Baron.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Madison Ballroom A
Biotic response to nitrogen deposition in the Colorado alpine: Priming the N cycle pump?
Bowman, William1, Steltzer, Heidimarie2, Suding, Katherine1, 1 2
ABSTRACT- Rates of nitrogen deposition in the Colorado Front Range are relatively modest, yet measurements of stream chemistry in high elevation catchments indicate N saturation is occurring. The response of alpine ecosystems to increasing rates of N deposition may be determined in large part by biotic changes. Significant changes in plant species composition occur in N fertilization experiments, determining the majority of the production response at the community level. Changes in plant species abundances have occurred over the past 10-50 years, with a close correspondence between species that are increasing in abundance and those that increase under fertilized conditions. Because much of the small-scale spatial variation in N cycling is associated with plant species composition, changes in the relative abundances of species can have a significant impact on N biogeochemistry in the alpine. In particular, species that are capable of greater growth under higher N supply have characteristics that enhance rates of N cycling relative to unresponsive species. This biotically-driven positive feedback resulting from N deposition in the alpine has important consequences for fluxes of N into surrounding aquatic ecosystems.
KEY WORDS: nitrogen deposition, alpine ecosystems, species effects on nitrogen cycling, biotic control of ecosystem function