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
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