We carried out an experiment to examine this phenomenon in living, whole canopies. We used Douglas fir grown under different fertilization treatments designed to induce differences in foliar nitrogen, incorporated mainly into non-pigment compounds, and the pigment chlorophyll, while minimizing changes in leaf structure, biomass, moisture and other biochemicals.
The work was supported by NASA under the Accelerated Canopy Chemistry Program (ACCP). The ACCP was designed to to research extent to which infrared spectroscopy for dried, ground plant materials could be extended to fresh leaves, whole canopies in laboratory and field settings, and entire ecosystems.
Douglas fir (Pseudotsuga menziesii (Mirb.) Franco.) seedlings were grown with different fertilization treatments in an experiment designed to investigate the effects of foliar biochemistry on needle and canopy reflectance measurements. Potentially confounding effects of the covariance of canopy structure with foliar biochemical concentration were minimized by fertilizing after leaf expansion. Seedlings showed no significant differences in specific leaf area, biomass or LAI, but showed significantly different total nitrogen concentrations, and some differences in chlorophyll concentrations. Measurements were made of needle optical properties and bidirectional reflectance was obtained of needles and of canopies. Canopy reflectance was acquired under sky illumination using two field spectroradiometers (photograph of experimental set-up).
This data set represents one of the few available in which needle and canopy reflectance measurements were acquired from the same trees. (To get the raw reflectance data, click here). These data, and the accompanying data on chlorophyll and nitrogen concentrations, tree shape, and structural variables, have the potential to be used to parameterize current canopy reflectance models which use leaf optical properties as a basis.
Results of this work can be read in two recent publications:
Dungan, J.L., L.F. Johnson, C.R. Billow, P.A. Matson, J. Mazzurco, J. Moen, and V.C. Vanderbilt (1996) High spectral resolution reflectance of Douglas fir grown under different fertilization treatments: Experiment design and treatment effects. Remote Sensing of Environment. 55:217-228.
Johnson, L.F. and C.R. Billow (1996) Spectrometric estimation of total nitrogen concentration in Douglas-fir foliage. International Journal of Remote Sensing. 17:489-500.
Jennifer Dungan, JCWS, Inc.
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