Relation of leaf image, chlorophyll fluorescence, reflectance and SPAD in rice and barley

Remote sensing tools such as SPAD, digital image analysis, reflectance and chlorophyll fluorescence have different advantages and limitations in evaluating plant physical ecology. It is very important to select the best one for the measurement. Few papers were found studying on the relationship between various remote sensing methods. Two experiments, one in 2009 and the other one in 2010, were conducted to study the relationship between these characteristics at a leaf scale. Three rice (M17, M15, Xiushui 09) and three barley (Hua 30, Zhepi 33, Zhexiu 12) were selected in our glasshouse experiment. The results showed that there was a highly significant relationship between R (red channel of the leaf image), G (green channel of the image), R550 (reflectance at 550 nm), photochemical reflectance index (PRI), and SPAD-502 readings (SPAD) for rice and barley. Close linear correlation was found between leaf chlorophyll maximal fluorescence (F_m), ratio of variable to maximal chlorophyll fluorescence (F_v/F_m) and SPAD reading for rice. However, no significant relationship between F_m, F_v/F_m and SPAD reading was found in barley. Linear and Logarithmic equations could be used to describe the relationship of R, G, R550, PRI, F_m, F_v/F_m and SPAD reading. It suggests that leaf image analysis has a stronger relationship with SPAD than reflectance or leaf chlorophyll fluorescence across the two species of rice and barley.