Actavia 0 Perera-Castro, A. V. Brito, P. González-Rodríguez, A. M. Changes in thermic limits and acclimation assessment for an alpine plant by chlorophyll fluorescence analysis: F<sub>v</sub>/F<sub>m</sub>vs. R<sub>fd</sub> 2018 2018-6-1 527-536 A comparison between maximum quantum yield of PSII photochemistry (F<sub>v</sub>/F<sub>m</sub>) and chlorophyll fluorescence decrease ratio (R<sub>fd</sub>) for low and high temperature resistance was assessed in a seasonal study of the acclimation in Pterocephalus lasiospermus. Analyzing the regression adjustment of both parameters and the lethal temperatures (LT<sub>50</sub>), R<sub>fd</sub> resulted in being a more sensitive indicator for low and high temperature treatments, since the thermic resistance estimated with R<sub>fd</sub> parameter was never higher than those estimated with F<sub>v</sub>/F<sub>m</sub>. Furthermore, the use of F<sub>v</sub>/F<sub>m</sub> led to an overestimation of the acclimation phenomena, with 6ºC of a maximum difference between both parameters. Using R<sub>fd</sub> as the indicator parameter, P. lasiospermus acclimated to low temperatures but it kept on being a sensitive species (the lowest LT<sub>50</sub> values only achieved-9.9 ± 0.3ºC). bserved (LT<sub>50</sub> around 43.5ºC). Thus, according to R<sub>fd</sub> evaluation of the thermic threshold, this species could be in risk of damage at low temperatures in this alpine ecosystem. 2 56