The potential of MODIS derived Photochemical Reflectance Index for studying gross primary productivity of oil palm trees

Many studies found that the Photochemical Reflectance Index (PRI) is sensitive to the light use efficiency (LUE) of biomes. LUE is one of the important variables for estimating gross primary productivity (GPP) which is concerned with the rate of carbon sequestration. Previous studies demonstrated that Moderate Resolution Imaging Spectroradiometer (MODIS) derived PRI can be used as a surrogate for LUE of vegetation at a regional scale. However, the relationship between MODIS PRI and LUE is not universal; it varies with biomes. This study investigated the potential of MODIS derived PRI for studying 1) oil palm GPP, and 2) the environmental factors namely temperature, vapour pressure deficit (VPD) and photosynthetically active radiation (PAR) in the tropics (Peninsular Malaysia). The relationship of PRI (surrogate for LUE) with the tropical environmental factors deserves studies because these regions have unique climate which is different from other latitudes and which plays an important role in the global climate system. In this study, MODIS daily PRI was derived from MODIS daily calibrated radiances products (MOD021km), oil palm GPP was derived from MODIS GPP products, and daily meteorological data (daily mean temperature, daily mean VPD and daily PAR) were collected from the Malaysian Meteorological Department. Our results showed that the MODIS PRI has relatively weak and negative asymptotic relationships with MODIS oil palm GPP (R²=0.21, p <; 0.001) and the environmental factors (R2 ranges between 0.14 and 0.25, p <; 0.001).