Abstract: The photochemical reflectance index (PRI) which is defined as a normalized difference index relating two narrow reflectance wavebands at 531 nm and 570 nm provides a reliable method to estimate light use efficiency (LUE) at the leaf, canopy and sight scales. Therefore, PRI opens a new era for estimating Net primary productivity（NPP）in a relatively high precision. However, a number of disturbances which change with scales will influence the relationship between PRI and LUE. Therefore, it is of great necessity and urgency to explore the influences of different disturbances at different scales on the relationship between PRI and LUE. In this analysis, sensitivity study was carried out at leaf and canopy scale based on PROSPECT and SAIL model respectively. The results proved that leaf PRI was sensitive to leaf biochemical components as leaf mesophyll structure parameter and chlorophyll a+b content while insensitive to dry matter content and equivalent water thickness. At canopy scale, canopy PRI was much influenced by leaf area index, leaf angle distribution, sun zenith angle and view zenith angle. Canopy PRI was depended on the intrinsic characteristic of canopy rather than the soil type of background.

Key words: Photochemical reflectance index (PRI), light use efficiency (LUE), leaf scale, canopy scale, sensitivity