PARENT SESSION
Wednesday, August 9, 1:30-5:00 pm
Symposium 13 - Mucking through multi-factor experiments: design and analysis of multi-factor studies in global change research
Ballroom B, Ballroom Level, Cook Convention Center
Organized by: AT Classen (classenat@ornl.gov)

This symposium will include talks that tease apart some of the complexities in multi-factor climate change experiments using current projects as examples, discuss creative ways to analyze complex results using mechanistic models, and discuss how to fully integrate models into future experimental designs.

Potential long term impacts of global change on C and N cycling in forest and grassland ecosystems.

Del Grosso, Stephen^{*,1, 2}, Parton, William², Adler, Paul³, Ojima, Dennis², ¹ USDA ARS, Fort Collins, CO² Colorado State University, Fort Collins, CO³ USDA ARS, University Park, PA

ABSTRACT- Field experiments have addressed the short term response of net primary productivity (NPP) to enhanced atmospheric CO₂, altered temperature and precipitation, and increased N inputs. However, modeling studies are necessary to investigate the long term impacts of global change on plant growth as well as other C and N flows such as heterotrophic respiration, N gas losses, and NO₃ leaching. The DAYCENT biogeochemical model was used to project the long term (100 year) impacts of global change on C and N fluxes for shortgrass steppe, tallgrass prairie, switchgrass grown for biofuel, boreal forest, and temperate coniferous forest ecosystems. All the systems modeled showed increased NPP with elevated CO₂ with and without increased temperature. Simulations that included increased atmospheric N deposition had the largest increase in NPP. N losses tended to decrease under elevated CO₂ as a single factor but increased if rising temperatures were simulated. Although absolute N losses increased as N inputs increased, the portion of N lost as a fraction of N inputs was lower when increased N deposition was simulated. Soil organic carbon (SOC) decreased at the arid shortgrass steppe. SOC increased or remained the same at the other sites under elevated CO₂ as a single favor but tended to decrease when rising temperatures were included. These model results are largely driven by the transitory impacts of global change and are expected to be different once the systems reach a new steady state.

Key words: global change impacts, carbon and nitrogen flows, modeling