PARENT SESSION
Oral Session #54: Vegetation: Controls on NPP, Global Climate Change. Presiding: W. Oechel.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.

Atmospheric constraints on physiological processes from CO₂ inversions.

Still, Christopher¹, Fung, Inez¹, Randerson, James², ^{1 2}

ABSTRACT- We present preliminary results of a new approach to using atmospheric CO₂ data to constrain physiological parameters of carbon exchange processes. Data on CO₂ concentrations collected at remote monitoring stations of the NOAA-CMDL network are combined with a biosphere model and an atmospheric transport model to perform a synthesis inversion. Rather than solving for regional-to-continental-scale carbon fluxes as is typically done, we solve for the light-use efficiency (LUE) of photosynthesis and the temperature sensitivity of respiration (Q10) for broad ecosystem types (e.g. temperate broadleaf forests). This approach has two clear advantages. First, the inferred parameter values are more directly comparable to local-scale measurements at eddy flux sites (i.e. AMERIFLUX) than are carbon fluxes because these parameters are likely to scale in space and time more easily than carbon fluxes. And second, an improved understanding of the biological and biophysical controls on carbon exchange processes is crucial for understanding carbon-climate interactions. Our preliminary results for high-latitude, northern-hemisphere ecosystems suggest a LUE of 0.4 g C/MJ PAR and a Q10 of 1.3 provide the best agreement with atmospheric CO₂ data. The optimal LUE:Q10 combinations for low-latitude ecosystems, however, are not as well constrained by the atmospheric data.

KEY WORDS: inversion, Q10, light use efficiency