HR: 1330h
AN: B22A-0803 INVITED     [PDF]
TI: Examining Light Use Efficiency in Multiple Ecosystems
AU: * Huemmrich, K F
EM: Karl.Huemmrich@gsfc.nasa.gov
AF: Joint Center for Earth System Science, University of Maryland Baltimore county Code 923.4 NASA/Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Gamon, J
EM: jgamon@calstatela.edu
AF: Center for Environmental Analysis (CEA-CREST), California State University, Los Angeles 5151 State University Drive, Los Angeles, CA 90032 United States
AU: Hall, F G
EM: fghall@ltpmailx.gsfc.nasa.gov
AF: Joint Center for Earth System Science, University of Maryland Baltimore county Code 923.4 NASA/Goddard Space Flight Center, Greenbelt, MD 20771 United States
AB: One approach to modeling the carbon uptake, or gross ecosystem exchange (GEE), is a light use efficiency (LUE) model. LUE models assume a linear relationship between the amount of photosynthetically active radiation (PAR) absorbed by the vegetation canopy and GEE. The slope of that relationship is called the efficiency (e). A key problem in using LUE is the determination of e, and understanding how it may vary both between ecosystems as well as over time. To examine this question, carbon dioxide flux data measured using eddy covariance techniques were combined with ground-based reflectance measurements to determine e on a daily basis over the course of a growing season for a variety of ecosystems, including deciduous forest, conifer forest, wetland, tundra, and prairie. The fraction of PAR absorbed by vegetation was derived from the Normalized Difference Vegetation Index (NDVI). For several sites usable values for NDVI could be calculated from measurements of incident and reflected PAR and shortwave radiation collected from the flux tower. This approach provides an indication of the ways in which remote sensing techniques can be used in conjunction with flux data to aid our understanding of ecosystem function. Daily values of GEE were compared with values for daily absorbed PAR. Values of e were generally consistent for a site throughout the year, allowing an annual value to be determined. Annual values for e were found to range from 1.4 g C/MJ for deciduous forest and grassland to 0.4 g C/MJ for the tundra, with R2 values generally over 0.8. Within the growing season for some sites periods of photosynthetic saturation were observed, examination of these periods assist in identifying sources of stress on the ecosystem.
DE: 0400 Biogeosciences
DE: 1851 Plant ecology
DE: 3322 Land/atmosphere interactions
DE: 3360 Remote sensing
SC: Biogeosciences [B]
MN: 2003 Fall Meeting