Frost damage in Pinus sylvestris L. stems assessed by chlorophyll fluorescence in cortical bark chlorenchyma

? Several techniques were used to investigate the threshold minimum temperature inducing severe frost damage during winter in Scots pine (Pinus sylvestris L.) needles and stems from southern provenances in the Iberian Peninsula.

? Chlorophyll (Chl) fluorescence, electrolyte leakage (EL), visual scoring (VS), and the normalized difference vegetation index (NDVI) were compared.

? Chl fluorescence, and in particular the maximum potential photosystem II (PSII) efficiency — estimated through the dark-acclimated F_V/F_M ratio-, was found to be a simple, non-destructive indicator of freezing tolerance in needles, as expected.

? Moreover, the existence of a Chl-containing tissue, the cortical bark chlorenchyma, allowed us the use of Chl fluorescence as a new non-destructive indicator of frost damage in live tissues of Pinus sylvestris L. stems.

? Freezing tolerance values of southern provenances are compared with those found by other authors in the northern distribution limit of the species.