HR: 0800h
AN: B31B-0322    [Abstracts]
TI: Incorporation of leaf Nitrogen Observations for Biochemical and Environmental Modeling of Photosynthesis and Evapotranspiration
AU: * Boegh, E
EM: eboegh@ruc.dk
AF: Roskilde University, Universitetsvej 1 Postbox 260, Roskilde, 4000, Denmark
AU: Gjetterman, B
EM: bgj@kvl.dk
AF: Dept. of Agricultural Sciences, Copenhagen University, Hoejbakkegaard alle 30, Taastrup, 2630, Denmark
AU: Abrahamsen, P
EM: abraham@dina.kvl.dk
AF: Dept. of Agricultural Sciences, Copenhagen University, Hoejbakkegaard alle 30, Taastrup, 2630, Denmark
AU: Hansen, S
EM: sha@kvl.dk
AF: Dept. of Agricultural Sciences, Copenhagen University, Hoejbakkegaard alle 30, Taastrup, 2630, Denmark
AU: Jensen, N
EM: nhj@ruc.dk
AF: Roskilde University, Universitetsvej 1 Postbox 260, Roskilde, 4000, Denmark
AU: Schelde, K
EM: Kirsten.Schelde@agrsci.dk
AF: Institute of Agroecolgy and Environment, Aarhus Universitet, Blichers alle postbox 50, Tjele, 8830, Denmark
AU: Soegaard, H
EM: hs@geogr.ku.dk
AF: Institute of Geography and Geology, Copenhagen University, Oester voldgade 10, Copenhagen K, 1350, Denmark
AU: Thomsen, A
EM: Anton.Thomsen@agrsci.dk
AF: Institute of Agroecolgy and Environment, Aarhus Universitet, Blichers alle postbox 50, Tjele, 8830, Denmark
AB: Lack of knowledge concerning regional and global nitrogen (N) availability and its impact on CO2 sequestration processes complicates the modeling of carbon cycle feedbacks to climate change. The use of remote sensing constitutes a valuable data source to quantify and investigate impacts of bulk leaf N contents, however information on the vertical leaf N distribution and its relation to photosynthetic (Rubisco) capacity should also be known to quantify leaf N impacts on canopy photosynthesis. In this study, impacts of the amount and vertical distribution of leaf N contents on canopy photosynthesis were investigated by combining field measurements and photosynthesis modelling. While most canopy photosynthesis models assume an exponential vertical profile of leaf N contents in the canopy, the field measurements showed that well-fertilized fields may have a uniform or exponential profile, and senescent canopies have reduced levels of N contents in upper leaves. The sensitivity of simulated canopy photosynthesis to the different (observed) N profiles was examined using a multi-layer sun/shade biochemically based photosynthesis model and found to be important; ie. for a well-fertilized barley field, the use of exponential instead of uniform vertical N profiles increased the annual assimilate by 12 percent. Perspectives for remote sensing based estimation of leaf N contents for photosynthesis modeling are finally discussed.
DE: 0400 BIOGEOSCIENCES
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting