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 v / F m 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 v / F m 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 v / F m showed a strong correlation with predawn photochemical reflectance index ((PRI p ), PRI = ( R 531 − R 570 ) / ( R 531 + R 570 ), where R = reflectance). For the data obtained at noon, Δ F / F m ′ showed a significant but weak correlation with PRI (PRI n ). However, stronger correlation between Δ F / F m ′ and ΔPRI (PRI p − PRI n ) was found. In addition, while a non-significant or weak correlation between non-photochemical quenching (NPQ) and PRI n was observed in species sensitive to low temperature, their NPQ was significantly correlated with ΔPRI. We conclude that PRI p 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.
Functional Plant Biology – CSIRO Publishing
Published: Mar 2, 2006
Keywords: noon, photochemical reflectance index, predawn, PSII efficiency, season.
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