Abstract
We linked a leaf-level C0
2 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 C0
2 uptake (A
nC) at the Duke Forest free-air C0
2 enrichment (FACE) study. Rates of A
nC estimated from the 4C-A model agreed well with leaf gas exchange measurements (A
net) in both CO
2 treatments. Under ambient conditions, monthly sums of net C0
2 uptake by the canopy (A
nC) were 13% higher than estimates based on eddy-covariance and chamber measurements. Annual estimates of A
nC 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 C0
2, the C used annually for growth, turnover, and resptration balanced only 80% of the A
nC Of the extra 700g Cm
-2a
-1 (1999 and 2000 average), 86% is attributable to surface soil CO
2 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 CO
2, net ecosystem production increased by 272g Cm
-2a
-1, 44% greater than under ambient CO
2. 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.
Keywords
Canopy stomatal conductance,
free air CO2 enrichment,
net ecosystem exchange,
net primary productivity,
plant canopy modelling,
respiration
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 CO
2 atmosphere alters carbon assimilation and allocation in a pine forest ecosystem. Global Change Biology (2003) 9, 1378-1400