Changes in thermic limits and acclimation assessment of an alpine plant by chlorophyll fluorescence analysis: Fv/Fm vs. Rfd
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A comparison between maximum quantum yield of PSII photochemistry (Fv/Fm) and chlorophyll (Chl) fluorescence decrease ratio (Rfd) in low and high temperatures resistance is assessed in a seasonal study of the acclimation of Pterocephalus lasiospermus. Analyzing the regression adjustment of both parameters and the lethal temperatures (LT50), Rfd resulted to be a more sensitive indicator parameter for low and high temperature treatments, since thermic resistance estimated with Rfd parameter was never higher than those estimated with Fv/Fm. Furthermore, the use of Fv/Fm led to an overestimation of the acclimation phenomena, with 6 Cº of maxima difference between both parameters. Using Rfd as indicator parameter, P. lasiospermus acclimated to low temperatures but it kept on being a sensitive species (the lowest LT50 values only achieved ¿9.9 ± 0.3ºC). However, any heat acclimation was observed (LT50 around 43.5ºC). Thus, according to Rfd evaluation of thermic threshold, this species could be in risk of damage for low temperatures in this alpine ecosystem.