Fig. 7. Heat of 40°C impaired PSII efficiency more than heat of 35°C while both induced NPQ.

Algal cultures harvested from PBRs before, during and after heat treatment at 35°C (a, c, e, g, i) or 40°C (b, d, f, h, i) were used for photosynthetic measurements. a–h Photosynthetic parameters measured using room temperature chlorophyll fluorescence. (a, b) PSII efficiency, the data at 0 μmol photons m⁻² s⁻¹ light are the maximum PSII efficiency in dark and data from light phase are PSII operating efficiency in light-adapted cells. c, d Linear electron flow, accounting for the changes of PSII antenna size during the treatments as in (i). e, f Q_A redox state, the redox state of chloroplastic quinone A (Q_A), the primary electron acceptor downstream of PSII; the bigger number of Q_A redox state means more reduced Q_A. g, h Nonphotochemical quenching, NPQ. i Relative PSII antenna fraction, percentage of light distributed to PSII measured by 77 K chlorophyll fluorescence. Mean ± SE, n = 3 biological replicates. Statistical analyses were performed using two-tailed t-test assuming unequal variance by comparing treated samples with the pre-heat samples under the same light (a–h, *) or constant 25°C samples at the same time point (i, *), or by comparing samples between 35°C and 40°C at the same time point (i, #). a–i P values were corrected by FDR. *, p < 0.05, the colors and positions of asterisks match the treatment conditions and time points, respectively. (i) #, p < 0.05, the positions of pound signs match the time points. e, f Not significant, ns.