PARENT SESSION
Contributed Oral Session 156: Grassland Resource Allocation, Dispersal, and Pollination
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal

Carbon fluxes in a spatially and temporally heterogeneous temperate grassland.

Risch, Anita¹, Frank, Douglas¹, ¹ Syracuse University, Syracuse, NY, USA

ABSTRACT- The net exchange of carbon dioxide (CO₂) between atmosphere and biosphere is mainly driven by carbon (C) fluxes associated with photosynthesis and respiration. In order to successfully predict and mitigate future increases in atmospheric CO₂, it is critical to understand how biotic and abiotic factors control plant C assimilation, and shoot, root and microbial respiration. In particular in grasslands, landscape position, soil properties, grazing and intra- and interannual variation in precipitation and temperature alter soil moisture, plant production, total plant biomass and species composition, which likely results in large spatial and temporal differences in plant and soil C fluxes. The goal of this study was to explore the interactions of grazing ungulates and topo-edaphic gradients on plant and soil C fluxes in grasslands of Yellowstone National Park. Carbon fluxes (net ecosystem C exchange, plant assimilation/respiration, dark and soil respiration), canopy and environmental variables were measured inside and outside long-term ungulate exclosures in dry to mesic grassland throughout the 2004 growing season. Our results showed no difference in C fluxes between the grazed and ungrazed sites. However, we detected large spatial and temporal differences in ecosystem C exchange. Carbon uptake and release across the landscape was associated with total aboveground biomass and plant N content, showing highest rates at the mesic, high productive sites. Overall, all sites showed a net C storage. The temporal variability in ecosystem C exchange was also correlated to total amount of aboveground biomass and were highest during the two summer month (July/August), while spring (May/June) and fall (September) measurements were considerably lower.

Key words: Yellowstone National Park, large ungulates, plant biomass and N, plant assimilation and respiration