Room temperature chlorophyll fluorescence
The activities of PSI and PSII were measured in dark-adapted (10 min) exponentially growing cultures with a Dual-PAM-100 system (Heinz Walz GmbH, Effeltrich, Germany) as described in Szyska et al. (2007). All samples were supplemented with 10 mM sodium bicarbonate and measurements were performed in a water-jacketed cuvette at the corresponding growth temperatures. The fluorescence parameters FV/FM(maximum photochemical efficiency), qL (proportion of open PSII reaction centers, assuming the “lake” model for antenna connectivity between reaction centers, qL=qP . [Fo′/FS]), Φ (PSII) (quantum yield of photochemistry, ΦPSII=(Fm ′ − Fs) /Fm′,), and NPQ (nonphotochemical energy dissipation from antenna quenching - Fm−Fm ′)/Fm′, were calculated during steady state photosynthesis (Kramer et al. 2004). Energy partition parameters for PSII were: ΦNPQ (ΦNPQ=1−ΦPSII−ΦNO) and ΦNO (energy dissipation from non-regulated processes- ΦNO=1/[NPQ+1+qL (Fm/Fo−1)]). Energy partition parameters of PSI were: quantum yield of PSI (ΦPSI), acceptor side limitation (ΦNA), and donor side limitation (ΦND) (Schreiber & Klughammer, 2008). All measurements were performed under temperature and irradiance values which matched the growth conditions.