Leaf Volume Reflectance: Better Estimate of Leaf Chlorophyll Concentration

Abstract:

Fifty-five years after H. Moldau of Tartu, Estonia reported that leaf surfaces polarize incident light, the remote sensing potential of polarization data of leaves and plant canopies is finally being investigated at a number of laboratories around the world. This research in our laboratory is testing whether the leaf volume reflectance – what remains after removing the polarized surface reflected light from leaf reflectance – provides improved estimates of leaf chlorophyll content.

Leaf reflectance, leaf volume reflectance and leaf surface reflectance were estimated in the laboratory for each of 21 leaves harvested from corn plants in the dent stage of development in a field nitrogen fertilization experiment. Leaf chlorophyll concentrations, measured in SPAD units using a SPAD-502 leaf chlorophyll meter (Konica Minolta, Osaka, Japan), ranged from low to high. Second order polynomial regression equations were fit to the leaf reflectance and leaf volume reflectance data to estimate leaf chlorophyll concentration within two wavelength bands: 570-650 nm and 705-715 nm; linear regression equations were fit to the leaf surface reflectance v. leaf chlorophyll concentration data in the same two wavelength bands.

Results show that the regression R-squared values were highest, 0.97 and 0.96, respectively, for the regression models using leaf volume reflectance measured in the 570-650 nm and 705-715 nm wavelength bands. Those values compare with r-squared values of 0.58 and 0.91, respectively, for leaf reflectance and 0.08 and 0.13, respectively, for leaf surface reflectance in the two wavelength bands.

We conclude that information about leaf chlorophyll concentration is in the leaf volume reflectance, not the leaf surface reflectance. Leaf reflectance, the sum of leaf volume reflectance and leaf surface reflectance, provides better information about leaf chlorophyll concentration when measured in the 705-715 nm wavelength band compared to the 570-650 nm band.