Changes in thermic limits and acclimation assessment for an alpine plant by chlorophyll fluorescence analysis: F-v/F-m vs. R-fd

A comparison between maximum quantum yield of PSII photochemistry (F-v/F-m) and chlorophyll fluorescence decrease ratio (R-fd) 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 (LT50), R-fd resulted in being a more sensitive indicator for low and high temperature treatments, since the thermic resistance estimated with R-fd parameter was never higher than those estimated with F-v/F-m. Furthermore, the use of F-v/F-m led to an overestimation of the acclimation phenomena, with 6 degrees C of a maximum difference between both parameters. Using R-fd as the indicator parameter, P. lasiospermus acclimated to low temperatures but it kept on being a sensitive species (the lowest LT50 values only achieved -9.9 +/- 0.3 degrees C). bserved (LT50 around 43.5 degrees C). Thus, according to R-fd evaluation of the thermic threshold, this species could be in risk of damage at low temperatures in this alpine ecosystem.