Fig. 2.

Effect of a 2.5-h exposure of R. glacialis individuals at different CO₂ concentrations on the formation of CPs and on catalase activity. Depending on the experimental conditions (ECs) the following CO₂ concentrations were applied: 1 38 ppm, 2 10,000 ppm, and 3 and 4 380 ppm. 1, 2 and 4 where exposed to natural solar irradiation (mean PPFD = 715 μmol photons m⁻² s⁻¹), while 3 was kept in darkness (grey boxes). a Relative proportion of chloroplasts with at least one chloroplast protrusion (rCP); b catalase activity in response to the different treatments; c rCP (black circles) of the light-exposed samples significantly correlates with the CO₂/O₂ ratio in accordance with a logarithmic function (solid line). This is also true for CAT activity (white circles, dashed line). Box plots: horizontal lines indicate the median and the 25th and the 75th percentiles; whiskers extend to 1.5 times box-height; circles represent outliers, asterisks indicate extreme outliers that have values more than three times box-height; black triangles indicate arithmetic means. Significant differences (P < 0.05) between groups are indicated by different characters (one-way ANOVA followed by Duncan’s (a) and Games-Howell (b) post hoc tests)