The effect of sub-zero temperatures in the light and dark on cold-hardened, dehardened and newly flushed white spruce (Picea glauca [Moench.] Voss) seedlings
1997
Gillies, S.L. | Binder, W.D.
Cold hardened, dehardened, and newly flushed foliage of one year old white spruce (Picea glauca [Moench.] Voss) seedlings were exposed to various sub-zero temperatures (- 2 to -22.5 degrees Celsius) either in the dark or light. The freezing treatment had no significant effect on the variable fluorescence to maximal fluorescence ratio (Fv/Fm) of hardened seedlings, either in the light or dark. Also, no visible damage or increase 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 Fv/Fm increased electrolyte leakage and visible damage were observed at warmer temperatures in newly flushed needles than in dehardened needles. Seedlings exposed to sub-zero treatments in the light also had lower Fv/Fm, 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 LT50 as estimated from visible damage data was -10.8 degrees Celsius in the light and -12.1 degrees Celsius in the dark for dehardened, one year old needles. The LT50 in newly flushed needles was -4.8 degrees Celsius in the light and 6.2 degrees Celsius in the dark. Recovery of Fv/Fm values 3 days after freezing exposure was only evident in treatments where little visible damage was present. Both Fv/Fm and electrolyte leakage were strongly correlated with visible damage.
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