PARENT SESSION
Contributed Oral Session 57: Polar and Alpine Ecology: Carbon and Nutrient Dynamics
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal

Investigating carbon cycling in tundra ecosystems on a naturally varying moisture gradient.

Nobrega, Sonia^*,1, Grogan, Paul¹, ¹ Queen's University, Kingston, Ontario, Canada

ABSTRACT- Soil moisture is an important control on carbon dioxide exchange yet it has received relatively little attention at the landscape scale. Measurements of CO₂ component fluxes amongst vegetation types in differing moisture conditions and manipulative experiments are critical to identifying mechanisms responsible for carbon uptake or loss and for predicting the long term dynamics of net carbon balance in the Arctic. In this study, we measured net ecosystem CO₂ exchange and ecosystem respiration rates twice a week through an entire growing season in three common vegetation types along a moisture gradient in an arctic tundra site in Canada's Northwest Territories. Furthermore, by manually removing all aboveground biomass and most roots from treatment plots, we estimated the relative contributions of plant associated and bulk soil organic matter carbon pools to ecosystem respiration. Data collected from the plot-scale sampling is used to assess relationships between CO₂ flux and measured environmental variables, such as light, air and soil temperature, and soil moisture. Measurements of CO₂ flux showed the wet sedge ecosystem acting as a net sink for CO₂ followed by the mesic birch hummock ecosystem over the study period. The results of our experimental manipulation indicate that plant-removal leads to a decrease in CO₂ flux as a result of decreased root respiration, and that this decrease is greatest in the wet sedge ecosystem. Data collected from an eddy flux tower is also used in a scaling up experiment, in order to characterize spatial dynamics in the relative contributions of different vegetation-types to overall net ecosystem exchange, and to test the plot scale flux sampling is representative and can be extrapolated to the region. Together, these results provide an indication of the growing season carbon budget of this Canadian Arctic site. Understanding the linkage between spatial variability and carbon efflux processes between the soil, microbial and plant pools will help us understand the carbon exchange between Arctic ecosystems and the atmosphere under predicted future climate change.

Key words: carbon dioxide flux, soil moisture, soil respiration, arctic tundra ecosystems