Effects Of Adaxial And Abaxial Surface On The Estimation Of Leaf Chlorophyll Content Using Hyperspectral Vegetation Indices

Vegetation indices are frequently used for the non-destructive assessment of leafchemistry, especially chlorophyll content. However, most vegetation indices weredeveloped based on the statistical relationship between the spectral reflectance of theadaxial leaf surface and chlorophyll content, even though abaxial leaf surfaces mayinfluence reflectance spectra because of canopy structure or the inclination of leaves.In the present study, reflectance spectra from both adaxial and abaxial leaf surfaces of Populus alba and Ulmus pumila var. pendula were measured. The results showed thatstructural differences of the two leaf surfaces may result in differences in reflectanceand hyperspectral vegetation indices. Among the 30 vegetation indices being tested,R672/(R550 × R708) had the smallest difference(4.66% for P. alba, 2.30% for U. pumila var. pendula) between the two blade surfaces of the same leaf in bothspecies. However, linear regression analysis showed that several vegetation indices(R850- R710)/(R850- R680), VOG2, D730 and D740, had high coefficients of determination(R2> 0.8) and varied little between the two leaf surfaces of the plants we sampled.This demonstrated that these four vegetation indices had relatively stable accuracy forestimating leaf chlorophyll content. The R2 valuesfor thecalibration of P. alba leaves were 0.92, 0.98, 0.93, and 0.95 on the adaxial surfaces,and 0.88, 0.87, 0.88, and 0.92 on the abaxial surfaces. R2 valuesfor the calibration of U. pumila var. pendula leaves were 0.85, 0.91, 0.86, and0.90 on adaxial surface, and 0.80, 0.80, 0.84, and 0.88 on abaxial surface. These fourvegetation indices were readily available and were slightlyinfluenced by the differencesin the two leaf surfaces during the estimation of leaf chlorophyll content.