Figure 1.

Variation in (a) photosynthetic activity at saturating light level (A_max), (b) stomatal conductance (g_s), (c) variable and minimal fluorescence ratio (F_v/F₀), and (d) relative water content (RWC) in leaves of Melissa officinalis plants exposed to charcoal-filtered air (open circle) or to 80 ppb of ozone (O₃; 5 h day⁻¹) for 35 consecutive days (closed circle). Data are shown as mean ± standard deviation (n = 5). For each parameter, p levels for the effects of the singular factor “O₃” and “time”, and their combination from a one-way repeated measures ANOVA are shown (***: p ≤ 0.001; **: p ≤ 0.01). According to Tukey’s HSD post hoc test, different letters indicate significant differences among means.