THE CONSEQUENCES OF FREEZING TEMPERATURES FOLLOWED BY HIGH IRRADIANCE ON IN-VIVO CHLOROPHYLL FLUORESCENCE AND GROWTH IN PICEA-ABIES

Picea abies (L.) Karst. plants, propagated by cuttings, were subjected to one night of freezing temperatures (-5 degrees C), high irradiance (1200 or 1800 mu mol m(-2) s(-1)), or freezing temperatures followed by high irradiance. The treatments were applied at bud burst, at time of shoot elongation, and when the shoots had ceased to elongate. The maximum quantum yield of photosynthesis, F-v/F-m, dry weight of branches and needles, and length and survival of shoots were measured. F-v/F-m and growth decreased after a night of freezing temperatures followed by high irradiance, at the time of bud burst and shoot elongation. High irradiance alone influenced F-v/F-m but not growth. Freezing temperatures affected F-v/F-m and growth at the time of shoot elongation. F-o increased after a night of freezing temperatures and decreased with age of the current-year needles. It was concluded that the use of short-term measurements of chlorophyll fluorescence induction to predict changes in growth after a night of frost and subsequent high light was not a reliable method.