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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 - Centro de Energia Nuclear na Agricultura (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.



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