THE EFFECT OF SUBZERO TEMPERATURES IN THE LIGHT AND DARK ON COLD-HARDENED, DEHARDENED AND NEWLY HUSHED WHITE SPRUCE (PICEA-GLAUCA [MOENCH] VOSS) SEEDLINGS

Cold hardened, dehardened, and newly flushed foliage of one year old w hite spruce (Picea glauca [Moench.] Voss) seedlings were exposed to va rious sub-zero temperatures (-2 to -22.5 degrees C) either in the dark or light. The freezing treatment had no significant effect on the var iable fluorescence to maximal fluorescence ratio (F-v/F-m) of hardened seedlings, either in the light or dark. Also, no visible damage or in crease in electrolyte leakage were evident in either the light or the dark treated seedlings. Both dehardened and newly flushed foliage were significantly affected by the freezing treatment, and light enhanced the effect. A decline in F-v/F-m increased electrolyte leakage and vis ible damage were observed at warmer temperatures in newly flushed need les than in dehardened needles. Seedlings exposed to sub-zero treatmen ts in the light also had lower F-v/F-m, increased electrolyte leakage and showed more visible damage than seedlings exposed to the same sub- zero treatments in the dark. The temperature where 50% of the needles were damaged (LT(50)) as estimated from visible damage data was -10.8 degrees C in the light and -12.1 degrees C in the dark for dehardened, one year old needles. The LT(50) in newly flushed needles was -4.8 de grees C in the light and -6.2 degrees C in the dark. Recovery of F-v/F -m values 3 days after freezing exposure was only evident in treatment s when little visible damage was present. Both F-v/F-m and electrolyte leakage were strongly correlated with visible damage.