PARENT SESSION
Oral Session #35: Nitrogen cycling: Response to inputs, variation in time and space. Presiding: M. Fenn.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Sphagnum moss responses to atmospheric nitrogen deposition: a conceptual model.
Aldous, Allison1,2, Bedford, Barbara1, 1 2
ABSTRACT- Sphagnum bogs are nutrient-poor ecosystems where plant growth is partly constrained by low nutrient levels. In these bogs, the entire water and nutrient supply is from atmospheric sources. Thus, as atmospheric deposition of nitrogen increases from anthropogenic activity, it is likely that the dominant Sphagnum mosses will be impacted directly. I propose a conceptual model of Sphagnum responses to increased atmospheric nitrogen deposition. I tested the model using my own data and data collected from the literature on unmanipulated populations of Sphagnum growing in regions with a range of nitrogen deposition. Model variables include Sphagnum tissue nitrogen and phosphorus concentrations, and net primary production. The data followed a three-phase model with critical thresholds at each level. Where atmospheric nitrogen deposition ranged from 0-1 g N m-2 year-1, nitrogen concentrations and the N:P ratio increased, but rates of nitrogen deposition explained less than 10% of the variation in primary production. Where nitrogen deposition ranged from 1-2 g N m-2 year-1, tissue nitrogen concentrations continued to increase but the N:P ratio leveled off. Available data on primary production were insufficient at intermediate and high levels of nitrogen deposition to determine the effects on Sphagnum growth. At deposition rates greater than 2 g N m-2 year-1, nitrogen concentrations began to decrease as did the N:P ratio. This model follows closely those of nitrogen saturation in temperate forests and nutrient limitation in Sphagnum mosses.
KEY WORDS: Sphagnum mosses, Nitrogen cycle, Atmospheric nitrogen deposition, Northern peatlands