HR: 0800h
AN: B51A-0930    [Abstracts]
TI: Inverse Estimation of Vc$_{max}$, LAI, and the Ball-Berry Parameter From Carbon and Energy Flux Measures.
AU: * Wolf, A
EM: awolf@ucdavis.edu
AF: Agronomy & Range Science, UC Davis, Davis, CA 95616 United States
AU: Laca, E A
EM: ealaca@ucdavis.edu
AF: Agronomy & Range Science, UC Davis, Davis, CA 95616 United States
AB: Ecosystem level fluxes of CO$_2$ and energy are modelled with high fidelity using a small number of environmental signals and a small number of seasonally-variant ecosystem parameters. Although these ecosystem parameters are invaluable for modeling canopy fluxes, they are not measured with nearly the same intensity as ecosystem fluxes themselves. An algorithm was developed to estimate leaf area (LAI), maximum carboxylation velocity (Vc$_{max}$), the Ball-Berry parameter {\bf m}, and substrate-dependent ecosystem respiration rate (\beta$_A$) by inverting a commonly-used modeling paradigm of canopy-level CO$_2$ and energy flux. Because these ecosystem parameters have collinear effects on CO$_2$ fluxes, energy flux measures are used to isolate different ecosystem attributes. LAI was solved by fitting the model to measured outgoing turbulent energy (H+LE); Vc$_{max}$ and \beta$_A$ were solved simultaneously by fitting to the flux of CO$_2$; {\bf m} was solved by varying the partitioning of available energy between H and LE. The results of the experiment showed that LAI, Vc$_{max}$, ecosystem respiration, and {\bf m} can be solved so that the carbon and energy fluxes can be modeled with R$^{2}$ from 80 to 95% and non-significant bias at 20-minute and daily timescales. LAI ranged from 2.0 to 2.4 over the season; Vc$_{max}$ declined from 20 to 5 \mu mol C m$^{-2}$ s$^{-1}$; respiration partitioning ranged from 0.5 to 0.75 (as a percentage of assimilation); {\bf m} varied between 17 and 24. These ecosystem parameters were consistent with independent measurements of the seasonal dynamics of the shortgrass steppe where they were evaluated, as well as literature values. In particular, {\bf m} must vary to accommodate changing energy partitioning over the course of the season. The ecosystem parameters are closely linked to mean daily fluxes of CO$_2$, but are not dependent on the environmental drivers during the periods when they are measured. Therefore, process-model inversion has potential for facilitating intercomparison of CO$_2$ and energy flux data among different sites and seasons by extending analyses from phenomenological to phenological considerations of ecosystem dynamics. This can add to the utility of flux data to provide essential land parameters for studies of climate dynamics.
DE: 1694 Instruments and techniques
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting