Fig. 4.
Effect of 20% CO2 in air on the stationary (Fs) and maximum fluorescence level (Fm) of Rhytidium rugosum. (A) Hydrated thallus darkened for 48 h to decrease zeaxanthin levels before measurement. (B). Thallus as in A, but also incubated for 2 h with 5 mM DTT before measurement. Modulated light to support fluorescence at the Fs level had a PPFD of 4 μmol m−2 s−1; the saturating light pulses (1 s) had a PPFD of 10,000 μmol m−2 s−1. Measuring beam (m. b.) was turned on and off and CO2 was increased as shown by arrows.