CD-02 Abstract

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

James Ehleringer, University of Utah (US-PI)
Luiz Antonio Martinelli, CENA/USP (SA-PI)

We propose two areas of research emphasis to better understand and constrain estimates of carbon dynamics in Amazônia ecosystems, based on progress during Phase I of LBA-ECO.  These are (1) field observations of stable isotope components of water and CO2 fluxes and (2) development of mechanistic leaf and canopy models to link with other projects evaluating ecosystem and regional carbon dynamics.

(1) Stable isotope analyses of atmospheric CO2 are one tool that scales processes from the soil and individual plant levels through to the troposphere.  We will apply 13C18O16O analyses as tools for better understanding gas exchange processes within ecosystems and regionally across ecosystems (forest, pasture, and river) in Manaus and Santarém.  These data will also directly contribute to regional and aircraft studies which rely on ground observations for their data interpretation.

(2) Mechanistic leaf, canopy and site-scale canopy-scale models including isotope exchange are tools for extrapolating from local scale measurements towards understanding carbon cycling on an ecosystem and a basin-scale.  Parameterized with leaf gas exchange characteristics (functional response curves, N values, 13C18O16O and, canopy structure) and driven by meteorological inputs, these models will be used to understand how climate influences carbon gain at the canopy-ecosystem scale and will be used to link with eddy covariance studies (NEE estimates), atmospheric sampling programs and regional carbon cycle modeling efforts as part of our science integration.

The proposed study will make several key LBA-Ecology measurements at two primary regions: Manaus and Santarém:

• leaf-scale parameters to parameterize canopy photosynthesis models

• canopy scale photosynthesis models driven by climate data

• d13C and d18O values of stocks in forest and pastures: leaves and soils

• d13C and d18O values of CO2 effluxing from soils and from the total ecosystem at forest and pasture sites

• d13C and d18O values of ecosystem photosynthetic discrimination in forests and pastures

• d13C and d18O values of landscape-level respiration (PBL)

Our studies will be conducted in close association with eddy covariance measurements, atmospheric CO2 sampling, and regional carbon modeling groups.  The leaf and canopy-level models of carbon gain and of isotope fractionation will linked directly with regional scale models. The information gathered using our isotope studies will help in determining the role of the Amazon Basin as a net sink or source of CO2 to the atmosphere.