Dual pam 100 chl fluorescence photosynthesis analyzer

Chlorophyll fluorescence, i.e., Fv/Fm, Φ_II, and NPQ was measured as described by Zhang et al. (2013 (link)) and Kramer et al. (2004 (link)). Dual-PAM-100 Chl fluorescence photosynthesis analyzer (Walz, Germany) was used to measure the chlorophyll fluorescence. 3 mL algal samples were dark-adapted for 15 min before measured. The maximum quantum yields of PSII electron transport was calculated as Fv/Fm = (Fm–Fo)/Fm, according to Kitajima and Butler (1975 (link)). The effective quantum yields of PSII electron transport was calculated as, Φ_II = (Fm'–F)/Fm', according to Genty et al. (1989 (link)) and Kramer et al. (2004 (link)). The non-photosynthesis quenching of PSII was calculated as NPQ = Fm/Fm'–1, according to Bilger and Björkman (1990 (link)).

Chlorophyll fluorescence was quantified using a Dual-PAM-100 Chl fluorescence photosynthesis analyzer (Walz, Germany). Intact cells from 22 and 4°C culture were adapted for 15 min in the dark at 22 and 4°C, respectively, prior to measuring their initial (Fo) and maximum (Fm) fluorescence levels. The maximum quantum yield of PSII photochemistry was calculated as Fv/Fm = (Fm − Fo)/Fm, as described by Geller et al. (2018) (link). The parameter 1-qL, which estimates the proportion of closed PSII reaction centers or the excitation pressure of PSII, was calculated using the following formula: 1-qL = 1 − [(Fm′ − F′) / (Fm′ − Fo′) × (Fo′/F′)]. The effective photochemical quantum yield of PSII was calculated as Y (II) = (Fm′ − F)/Fm (Kramer et al., 2004 (link)). The non-regulated energy dissipation Y (NO) was calculated as Y(NO) = F/Fm. The regulated energy dissipation Y (NPQ) was calculated as Y (NPQ) = F/Fm′ − F/Fm (Kramer et al., 2004 (link)). Y (ND), the non-photochemical energy dissipation caused by donor-side limitations, was calculated as Y (ND) = (P − Po)/Pm. Transient increases in chlorophyll fluorescence after turning off actinic light (AL) were detected as described by Shikanai et al. (1998) (link).