Ecosystems with little or no plant cover are often described as barren, however these systems can host diverse microbial communities. Yet, the biological functioning of these soils in high-altitude mountain ecosystems is poorly understood. We measured soil CO₂ fluxes and used molecular techniques to determine the composition of the bacterial and eukaryotic community at “barren” high-elevation sites in Colorado.

Elevational Controls on Organic and Inorganic Nutrients in Stream Waters, Boulder Creek Watershed, Colorado Front Range

Jordan N. Parman and Mark W. Williams

Department of Geography and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA

Nitrate deposition in terrestrial and aquatic ecosystems is increasing worldwide as a result of human activities. Between 1984 and 1996, deposition of inorganic nitrogen in Colorado’s Niwot Ridge Long Term Ecological research site doubled. Previous research suggests that small streams are the most effective sites for nitrate processing and retention; however, the role of alpine lakes has not been adequately examined.

Diverse plant litter mixtures frequently decompose substantially differently than expected, compared to the average of the individual component species. These strong “non-additive” effects constitute an important way in which biodiversity influences key components of below-ground ecosystem function like soil C and N cycling, and it remains unclear which plant traits drive diversity effects on soil C and N cycling.

Exposure to progressive inputs of anthropogenic N deposition elicits a series of changes in terrestrial ecosystems associated with both enhancement and inhibition of biogeochemical processes. Initially, growth of plants is enhanced as the constraint of N supply on NPP is relaxed, sometimes associated with altered dominance of species and gains or losses in diversity. Higher rates of nitrification and leaching of base cations eventually lead to acidification of soils, increases in soluble aluminum, and potentially to decreases in rates of NPP.

Green Lake 4 is an alpine lake in the Silver Lake Watershed of Boulder Colorado. Many alpine lakes similar in productivity and elevation to Green Lake 4, have shown a recent shift in diatom species. Nitrogen has been shown to be increasing in alpine lake systems of the Rocky Mountain Front Range due to atmospheric deposition. Species associated with oligotrophic systems are being replaced with more common species that are tolerant of higher nutrient concentrations. However, little is known about the role phosphorous.

Human activities have increased the amount of available nitrogen (N) globally. Increased N-availability can change plant community structure and function, and lead to diversity loss. Species traits associated with differential resource limitation may predict how plant communities will respond to N-enrichment across ecosystems. We focused on specific leaf area (SLA), leaf area per unit leaf mass, as a candidate trait because it is correlated with high relative growth rates, photosynthetic rates, and leaf N-concentrations.

Changing global climate patterns may have a significant impact on plant phenology. In the northern hemisphere plants have responded to warmer temperatures by flowering earlier and sustaining longer periods of growth. Changes in atmospheric N deposition and precipitation may also affect plant phenology. We tested the effects of increased winter precipitation, summer temperature and nitrogen (N) on plant phenology in an alpine moist-meadow community at the Niwot Ridge LTER site. Treatment effects were simulated using snowfences, open-top warming chambers and N fertilizer in 1 m2 plots.