The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008 - 2:40 PM
Multiple Climatic Changes and the Structure and Function of Ecosystems: Effects of Atmospheric Carbon Dioxide, Warming, and Soil Moisture on An Oldfield Ecosystem
Paul Kardol, Aimee T. Classen, and Richard J. Norby. Environmental Sciences Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN TN 37831-642
Ecosystems are complex and global change encompasses factors such as an increasing atmospheric concentration of carbon dioxide, rising temperature, and altered precipitation regimes. Multi-factor experiments are a necessary step in determining the potential for interactive effects of various factors of global change on both above and belowground response variables because they greatly increase the conceptual and analytical complexity of manipulative global change projects. The Old-Field Community Climate and Atmosphere Manipulation (OCCAM) experiment was initiated to assess the combined and interactive effects of [CO2], warming, and altered soil moisture on old-field ecosystems. After three years, we have found that the relative importance of single factor vs. interactive effects varied among years and depended on the response measured. For example, total aboveground net primary productivity (NPP) was 60% greater in wet plots than in dry plots, but it was unaffected by single factor or interactive effects of the manipulated variables. Soil nitrogen availability also was greater in wet than in dry plots, but was unaffected by [CO2] or warming. In contrast, effects of [CO2], warming, and soil moisture on leaf area index (LAI) in 2004, though statistically significant, varied strongly with time; in 2005, temporal variation in LAI was controlled by [CO2] alone. Green tissue [N] in 2004 was lower in elevated [CO2] treatments than in ambient [CO2], and was not affected by the manipulated variables. The idiosyncrasies of even this constructed system multi-factor experiment suggest that predicting the integrated response of whole ecosystems to multiple climate change factors will be a daunting, though critical, challenge for ecologists.