Fig. 2. Determining the true light saturated F^'_M by the three-pulse method. Apparent F^'_M was determined for three 0.8-s pulses of different PPFD, then the light-saturated F^'_M (at infinite PPFD) was estimated as the intercept of the linear regression of apparent F^'_M on the inverse of PPFD during the pulse. Example data are shown for leaves from each of the three water stress treatments in Exp. 1. Actinic PPFD during the measurement was 1500 µmol m^–2 s^–1 in every case.