THE CONSEQUENCES OF FREEZING TEMPERATURES FOLLOWED BY HIGH IRRADIANCEON 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 m aximum quantum yield of photosynthesis, F-v/F-m, dry weight of branche s 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. Hi gh irradiance alone influenced F-v/F-m but not growth. Freezing temper atures 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 shor t-term measurements of chlorophyll fluorescence induction to predict c hanges in growth after a night of frost and subsequent high light was not a reliable method.