Correlation of Chlorophyll Meter Readings with Gas exchange and Chlorophyll Fluorescence in Flag Leaves of Rice (Oryza sativa L.) Plants

The objective of this study was to establish the correlation of the chlorophyll meter (SPAD) readings with the contents of chlorophyll and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the gross photosynthetic rate (P(G)), and the maximum quantum yield of photosystem II (PSII) (F(v)/F(m)) in flag leaves of rice (Oryza sativa L.) in ripening stage. The SPAD readings significantly correlated with the Chl content, the Rubisco content, P(G) and F(v)/F(m) (R(2) = 0.848, 0.648, 0.671 and 0.712, respectively), which suggests that the SPAD meter has the potential to estimate the photosynthetic capacity of the flag leaves. However, both P(G) and F(v)/F(m) had a stronger relationship with the Rubisco content than the SPAD readings indicating that the PSII photochemical and CO(2) assimilation capacities are strongly influenced by the Rubisco content. Therefore, accurate calibration would be indispensable to obtain the physiological information from the SPAD readings of flag leaves.