Wednesday, November 15, 2006 - 10:45 AM

Measurement of Soil- and Ecosystem-Respired Δ13CO2 in Complex Mountainous Terrain.

Elizabeth Sulzman, Zachary Kayler, Mark Hauck, Thomas Pypker, Barbara Bond, Alan Mix, and William Rugh. Oregon State Univ, Dept of Crop and Soil Science, Corvallis, OR 97331

In a project we call the “Andrews Airshed study” located in western Oregon Cascades, we are measuring the carbon isotopic composition of soil- and ecosystem-respired CO2 to assess soil-vegetation-atmosphere interactions in steep mountainous terrain. Many of the world’s most productive ecosystems lie in mountainous terrain, yet most traditional ecological tools are not well-adapted to these systems. We are taking advantage of cold air drainage systems that are naturally regenerated in these systems to trap and mix ecosystem respired CO2; we are testing the hypothesis that we can infer ecosystem-level responses to climatic drivers from measurements of CO2 isotopes. Data indicate that isotopic values of ecosystem respiration reflect soil moisture more than vapor pressure deficit, contrary to results published for other systems. Surprisingly, soil moisture appears to be a weaker control on 13CO2 respired by soil organisms. Our measurements show pronounced diel variation in carbon isotopes in soil-respired CO2 that may indicate a very rapid response (on the scale of hours) of belowground respiration to carbon substrates provided by plants. Also intriguing is the finding that the isotopic composition of soil-respired CO2 is consistently enriched (by at least 1 per mille) on the south-facing, as compared to the north-facing slope. Current efforts are focused on teasing apart landscape-scale differences in soil properties, microclimate, and species composition as controls on the isotopic composition of ecosystem respiration. Our long-term goal is to “invert” an understanding of isotopic variation in ecosystem respiration to monitor intra- and inter-annual variations in ecosystem metabolism on a basin scale.