Evaluation of factors causing reflectance differences between Sun and Shade Leaves

Shade and sun leaves of Valencia orange [ Citrus sinensis (L.) Osbeck] were collected to evaluate comparative effects of their leaf chlorophyll concentration, water content, thickness, and mesophyll volume of air on visible light reflectance, specifically the 0.45-, 0.55-, and 0.65-μm wavelength (WLs). The reflectance at the 0.45-, 0.55-, and 0.65-μm WLs of sun leaves but not shade leaves was negatively correlated with total chlorophyll concentration. Reflectance at the 0.45-μm WL was affected by leaf water content for both sun and shade leaves. Sun leaf reflectance at the 0.45-μm WL, but not shade leaf reflectance was affected significantly by leaf mesophyll air volume. The effect of leaf thickness on reflectance was apparently of less importance than that of the chlorophyll content, air volume, and water content. The influence of shade and sun leaves on visible light reflectance/absorptance of at least Valencia orange tree canopies probably should be considered in modeling canopy reflectance and growth.