The effect of photoperiod and thermoperiod on cold acclimation and growth of Pinussylvestris

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Abstract
Low temperature acclimation and growth of roots and shoots of Scots pine seedlings (Pinussylvestris L.) under long day or short day (SD), and warm temperature or low temperature (LT) treatments were compared. Three methods were used to evaluate shoot injury; measurement of electrolyte leakage, regrowth, and visual microscopic evaluation were also compared to determine their usefulness in root injury evaluation. Visual evaluation was the most accurate and convenient technique for assessing LT root injury. Under all treatments shoots were hardier than roots with maximum hardiness of −40 and −15 °C, respectively, induced by SD/LT treatment. Stems acclimated and ceased growth in response to SD and LT, while only LT induced root acclimation and growth cessation. SD treatment does not induce substantial root cold acclimation and it reduces root growth primarily by limiting the availability of assimilates. White root tips were acclimated to −10 °C and did not affect the cold hardiness of more mature portions of the root.