Relationships between chlorophyll fluorescence parameters and photochemical reflectance index of tree species adapted to different temperature regimes.

Chlorophyll fluorescence parameters and spectral reflectance at leaf level were measured at both predawn and noon, under different temperatures and natural light conditions from autumn to winter. Predawn F / F of both mango (Mangifera indica L.), a tropical fruit tree, and Podocarpus nagi Zoll. et Moritz., a subtropical conifer, decreased with decreasing temperature, with the former to a greater extent than the latter. Yet, predawn F / F of Taiwan alder (Alnus formosana Makino), a broadleaf tree widely distributed from the lowlands to 3000 m above sea level in Taiwan, was less influenced by temperature. Nevertheless, taking all three species into consideration, predawn F / F showed a strong correlation with predawn photochemical reflectance index [(PRI), PRI = (R - R) / (R + R), where R = reflectance]. For the data obtained at noon, ΔF / F' showed a significant but weak correlation with PRI (PRI). However, stronger correlation between ΔF / F' and ΔPRI (PRI - PRI) was found. In addition, while a non-significant or weak correlation between non-photochemical quenching (NPQ) and PRI was observed in species sensitive to low temperature, their NPQ was significantly correlated with ΔPRI. We conclude that PRI can serve as an indicator of the seasonal variation of potential PSII efficiency; and ΔPRI reflects the actual photodissipation as well as actual PSII efficiency during illumination. For the three species in this study, the PRI provides a more consistent measure of the variation in predawn fluorescence values than for steady-state values measured under normal seasonally varying daylight illumination.