Measurement of the chlorophyll fluorescence induction kinetics with a 10 microseconds time resolution and its...

Measurement methods are described which determine the initial phase of the fluorescence induction kinetics with a maximum time resolution of 10 microseconds simultaneously for the two fluorescence components F685(t) and F730(t) selected by filters at the wavelengths 685 nm and 730 nm, respectively. The excitation light provided by a He-Ne laser (632.8 nm) is switched on within 0.3 microseconds (maximum intensity Ie = 12 mW/cm2). Fo, Fp, and Fs, the initial-, peak-, and steady-state intensity and the initial value Ro of the ratio R(t) = F730(t)/F685(t) can accurately be determined as well as the initial time derivative Fo* of the fluorescence intensity. Fo and Fo* are related to the quantum yield phi a of the antenna and to the photochemical quantum yield phi pc, respectively. Spruce, oak, birch, poplar, and soy bean show a decline of R(t) from Ro to a first minimum Rb at some 10 ms which has a similar value as the second minimum Rp in the time range of seconds. Furthermore, the initial value Ro and the steady-state value Rs of R(t) are also very similar. Measurements on spruce with water deficiency and with varying excitation light intensity Ie show effects on the initial phase of the fluorescence induction kinetics. Further measurements on spruce of different damage classes indicate that for the current year's needles the ratio Fp/Fo is the most sensitive parameter to differentiate between the damage classes and that Fo/Fs and Ro/Rb are also affected. As demonstrated by measurements on leaves of soy beans, the initial decrease of R(t) from Ro to Rb originates from a change of the fluorescence spectrum because no change of the leaf transmission can be observed in the time range between 10 microseconds and 1 ms.