Clonal variation in gas exchange and freezing tolerance development of interior spruce (Picea glauca (Moench) Voss x P-engelmannii Parry ex Engelm.) during autumn acclimation

Variation in physiological response during autumn acclimation was investiga ted in somatic seedlings of 10 interior spruce (Picea glauca (Moench) Voss x P. engelmannii Parry ex Engelm.) clones from five full-sib families. Expe riments were conducted on 2-yr-old seedlings through simulation in a growth . chamber. Throughout the experimental period, gas-exchange parameters (net photosynthesis, stomatal conductance to water vapour and instantaneous wat er-use efficiency) were measured weekly and freezing tolerance was determin ed five times. Results showed that as seedlings acclimated to decreasing ai r temperature and photoperiod, stomatal conductance decreased linearly, pho tosynthesis was unchanged until air temperature and photoperiod were below 10 degrees C and 11 h, respectively, water-use efficiency nearly doubled an d freezing tolerance increased in a curvilinear fashion. There was signific ant between- and within-family clonal variation in all of these physiologic al parameters.