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    Author(s): Karina V.R. Schafer; Ram Oren; David S. Ellsworth; Chun-Ta Lai; Jeffrey D. Herricks; Adrien C. Finzi; Daniel D. Richter; Gabriel G. Katul
    Date: 2003
    Source: Global Change Biology (2003) 9, 1378-1400
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (1.8 MB)

    Description

    We linked a leaf-level C02 assimilation model with a model that accounts for light attenuation in the canopy and measurements of sap-flux-based canopy conductance into a new canopy conductance-constrained carbon assimilation (4C-A) model. We estimated canopy C02 uptake (AnC) at the Duke Forest free-air C02 enrichment (FACE) study. Rates of AnC estimated from the 4C-A model agreed well with leaf gas exchange measurements (Anet) in both CO2 treatments. Under ambient conditions, monthly sums of net C02 uptake by the canopy (AnC) were 13% higher than estimates based on eddy-covariance and chamber measurements. Annual estimates of AnC were only 3% higher than carbon (C) accumulations and losses estimated from ground-based measurements for the entire stand. The C budget for the Pinus taeda component was well constrained (within 1% of ground-based measurements). Although the closure of the C budget for the broadleaf species was poorer (within 20%), these species are a minor component of the forest. Under elevated C02, the C used annually for growth, turnover, and resptration balanced only 80% of the AnC Of the extra 700g Cm-2a-1 (1999 and 2000 average), 86% is attributable to surface soil CO2 efflux. This suggests that the production and turnover of fine roots was underestimated or that mnycorrhizae and rhizodeposition became an increasingly important component of the C balance. Under elevated CO2, net ecosystem production increased by 272g Cm-2a-1, 44% greater than under ambient CO2. The majority (87%) of this C was sequestered in a moderately long-term C pool in wood, with the remainder in the forest floor-soil subsystem.

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    Citation

    Schafer, Karina V.R.; Oren, Ram; Ellsworth, David S.; Lai, Chun-Ta; Herricks, Jeffrey D.; Finzi, Adrien C.; Richter, Daniel D.; Katul, Gabriel G. 2003. Exposure to an enriched CO2 atmosphere alters carbon assimilation and allocation in a pine forest ecosystem. Global Change Biology (2003) 9, 1378-1400

    Keywords

    Canopy stomatal conductance, free air CO2 enrichment, net ecosystem exchange, net primary productivity, plant canopy modelling, respiration

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