Tuesday, August 3, 2010 - 8:40 AMOOS 13-3: Interactive impacts of CO2 and nutrients on forest production
William J. Parton, Colorado State University and Nceas Modelling Group, National Center for Ecological Analysis and Synthesis.
Background/Question/Methods Results from the ORNL FACE experiment suggest that an observed initial increase in plant production on elevated CO2 plots is reduced after 10 years due to increasing nutrient stress, while results from the Duke FACE show increased plant production on elevated CO2 plots throughout the 15 year experimental record. The NCEAS Elevated CO2 Model Comparison Project was proposed to compare the impacts of nutrients on ecosystem dynamics represented in ecosystem models and to assess model efficacy in simulating observed patterns of plant production under elevated CO2 at the ORNL and Duke FACE sites. The participant models allow soil nitrogen availability to influence soil and plant C:N ratios, plant photosynthetic rates, carbon allocation to the different plant parts, and overall amount of plant growth. Some of the models also include the impact of elevated CO2 levels on soil N fixation and nitrogen losses (as N2O, NOx, and NO3).
Results/Conclusions
Model results suggest that allowing the plant and soil C:N ratios to increase with decreasing nitrogen availability reduces nutrient down regulation of elevated CO2 plant production increases. This paper focuses on soil nutrient availability impacts on ecosystem models and how well these models represent the impacts of elevated CO2 at the Duke and ORNL FACE sites. The models with a dynamic carbon allocation scheme and variable plant and soil C:N ratios were more effective at replicating observed responses of the ORNL and Duke FACE sites to elevated CO2 levels.