In 2007 and 2008, A and E were measured on the highest fully-expanded leaf of 3 and 16 replicates, respectively, in each treatment. Leaves were kept as close to their natural angle as possible (nearly horizontal) while maximizing solar irradiance. In both experiments, A and E were measured at the same times as the gs measurements (see Section 16.2.4) using a portable open photosynthesis system (CI 340, CID, Inc., Camas, WA, USA). In 2004, A and E were measured on 9 replicates in each treatment using a closed photosynthesis system (LiCOR LI-6200, LiCor, Inc, Lincoln, NE, USA).
Photosystem (PS) II quantum efficiency (0PSn = (Fm-Fo)/Fm; Fo = minimum fluorescence yield of dark-adapted leaves, Fm = maximum fluorescence of dark-adapted leaves) was estimated during the 2007 experiment before dawn (700 LT) and after dusk (2100 LT) of each day of exposure. Photosystem II yield (^pSn = (Fms-Fo)/Fms; Fs = steady state after exposure to a light source that drives photosynthesis, Fms = maximum fluorescence of leaves after exposure to a light source that drives photosynthesis) was estimated during the 2008 experiment at 6 hours (Day 1), 30 hours (day 2), 52 hours (Day 3), and 77 hours (Day 4) after the start of the experiment. Maximal fluorescence with all PS II reaction centers in the closed state was induced by a 0.8 s saturating pulse of white light (3,000 ^mol m s ). After 10 s, the actinic light was turned on and the same saturating pulse described previously was applied every 1 s, until steady-state photosynthesis was reached in order to obtain Fs or Fm. Measurements were made using the CI-340 portable photosynthesis system with a pulse-modulated CI-510CF Chlorophyll Fluorescence Module (CID, Inc., Camas, WA, USA).
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