Seasonal Dynamics of Chlorophyll Fluorescence in the Evergreen Peumus boldus and the Semideciduous Colliguaja odorifera Under Field Conditions

We used chlorophyll fluorescence techniques to investigate seasonal variations in photosystem II (PSII) quantum yield in five-year-old saplings of the sclerophyllous <i>Peumus boldus</i> Molina (evergreen) and <i>Colliguaja odorifera</i> Molina (semideciduous) planted in a semiarid site with a Mediterranean-type climate. Chlorophyll fluorescence rise kinetics (OJIP) were monitored monthly for one year (September 2024 to September 2025). With this information, we estimated the relative deviation of the performance index (PI_ABS) of each species from the average PI_ABS in each season (denoted as ∆PI_ABS). <i>P</i>. <i>boldus</i> was associated with destruction of PSII reaction centers and incapacity for electron transport, i.e., higher values of parameters ABS/RC (effective antenna size of an active reaction center) and F₀ (minimal fluorescence), whereas <i>C</i>. <i>odorifera</i> was associated with higher photosynthetic performance i.e., higher values of PI_ABS, PI_TOT (total performance index), F_V/F₀ (ratio between variable and minimal fluorescence), and F_V/F_M (maximum quantum yield of primary PSII photochemistry). P_IABS exhibited a 52 and 38% reduction (i.e., -∆PI_ABS) during spring and winter in <i>P</i>. <i>boldus</i>, but an increase (i.e., +∆PI_ABS) of 52 and 37% in the same seasons for <i>C</i>. <i>odorifera</i>. <i>P</i>. <i>boldus</i> was considerably more depressed during the winter-spring season than the summer months. This suggests that PSII function in <i>P</i>. <i>boldus</i> is more sensitive to low temperatures in winter and spring than the lack of water and high temperatures during summer.