Long-Term Response of an Arctic Sedge to Climate Change: A Simulation Study.

It appears that polar regions of the Earth will bear the brunt of global temperature increases. Because of the ecological importance of the sedge Eriophorum vaginatum in the arctic and the large amount of data available on its growth and physiology, we chose this species as a test case to model the potential long-term response of arctic plants to global climate change. Our simulation model utilizes a mechanistic framework and includes the effects of light, temperature, season length, nitrogen availability, and CO concentration on E. vaginatum growth dynamics. The model was parameterized based on a series of published studies of the growth responses of E. vaginatum to nutrients and validated using (1) field studies on the growth responses of E. vaginatum to temperature and shading, and (2) the effects of elevated CO and temperature on E. vaginatum photosynthesis. The effect of a 50-yr period of climate change on peak biomass (overwintering biomass plus seasonal production) in E. vaginatum was explored. We use climate change here to refer to linear increases over a 50-yr period in temperature (from 8° to 13°C), season length (from 100 to 120 d), and atmospheric CO (from 340 to 680 @mL/L). Similarly, a wide range of nitrogen availabilities (from 9 to 18 g°m °yr ) was also examined because of its importance in productivity. The model predicts that a simultaneous increase in the direct effects of temperature, season length, and CO , with no change in nitrogen availability, will result in a slight decrease in peak biomass. A simulated long-term doubling of nitrogen availability results in an °70% increase in peak biomass, whereas with concurrent changes in climate and nitrogen availability, the model predicts a slight decline in peak biomass compared to increases in nitrogen alone. In essence, the model predicts that climate change will have substantial effects on E. vaginatum only indirectly through changes in nitrogen availability. Simulated peak biomass responds linearly up to a doubling of current nitrogen availabilities. Therefore, at low-to-moderate increases in nitrogen availability, the predicted response of E. vaginatum to climate change is linearly (and almost exclusively) dependent on our ability to predict the effects of climate change on nitrogen cycling. At nitrogen availabilities >2x current availabilities, the relationship flattens out very rapidly because the plant becomes limited by carbon uptake. Thus, if nitrogen availabilities more than double in the future, E. vaginatum may shift from being a nutrient-limited to a carbon-limited system and, consequently, increased season length and elevated CO concentrations may play an important role in controlling E. vaginatum productivity.