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One‐dimensional multilayer biosphere‐atmosphere models (e.g., CANVEG) describe ecosystem carbon dioxide (CO₂) and water vapor (H₂O) fluxes well when cold temperatures or the hydrologic state of the ecosystem do not induce stomatal closure. To investigate the CANVEG model framework under such conditions, CO₂, H₂O, and sensible heat fluxes were measured with eddy‐covariance methods together with xylem sap flux and leaf‐level gas exchange in a 16‐year‐old (in 1999) southeastern loblolly pine forest. Leaf‐level gas exchange measurements, collected over a 3‐year period, provided all the necessary biochemical and physiological parameters for the CANVEG model. Using temperature‐induced reductions of the biochemical kinetic rate constants, the CANVEG approach closely captures the diurnal patterns of the CO₂ and H₂O fluxes for two different formulations of the maximum Rubisco catalytic …