Carbon and Oxygen Isotope Ratio CO2 Flux Analyses at the Soil, Canopy, and Landscape Levels


Our research focuses on using stable isotope ratio measurements of atmospheric CO2 to infer changes in terrestrial ecosystem photosynthesis and respiration (sink or source strength) on local and regional scales. Within terrestrial ecosystems, photosynthesis and respiration have different and contrasting effects on the carbon and oxygen isotope ratio of atmospheric CO2. Monitoring shifts in both the concentration and stable isotope ratio of atmospheric CO2 can be used as a tool to study large scale terrestrial ecosystem gas exchange processes. This approach, often called a Keeling-plot analysis, estimates the integrated isotopic composition of CO2 leaving the ecosystem. The approach can also be scaled to look at sub-canopy as well as landscape-level patterns. Our research is part of the broader LBA-Ecology efforts (project CD-02).

Our project includes a nested sampling scheme for measuring isotope effects associated with photosynthesis and respiration at three spatial scales: (i) individual leaf and soil patch; (ii) canopy tower for canopy and/or ecosystem level; (iii) aircraft sampling of changes in the convective boundary layer for the regional level. Our research plan will allow us to determine the impacts of land-use changes (conversion of C3 forest to C4 pasture grasses), since C3 and C4 plants have very different isotope effects during photosynthesis. Interannual variability associated with El Niño/ La Niña events should also have substantial effects on the timing and magnitude of ecosystem gas exchange processes and associated isotope effects. Direct measurements of the effects of El Niño/ La Niña events on isotope effects during photosynthesis and respiration are needed for future large scale isotope modelling studies.

Our study is currently collecting LBA-Ecology measurements at Ji Parana, Manaus, and Santarem.

Our studies will be conducted in close association with simultaneous eddy covariance measurements, made by other researchers, in order to obtain information about ecosystem photosynthesis, respiration and turbulent exchange.

Tomas Domingues will complete his PhD thesis research as part of our LBA effort. Tomas' research will focus on describing the photosynthetic gas exchange attributes of key ecosystem components within the primary forest and pasture sites during both wet and dry seasons in Manaus and Santarem.

Jean Ometto will complete his postdoctoral training as part of our LBA effort. In addition to participating in analyses of organic matter and Keeling-plot analyses, Jean's research will focus on interpetation of the 18-O signal within CO2 as it is influenced by leaf water, source water, atmospheric water, and canopy structure.

Matrix overview of research plans




For general information about the Brazil-U.S. LBA effort, please visit the LBA home page.

For information about all available LBA data sets, please visit the ORNL-DAAC server.