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 investigated in somatic seedlings of 10 interior spruce (Picea glauca (Moench) Voss × P. engelrnannii Parry ex Engelm.) clones from five full-sib families. Experiments 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 water-use efficiency) were measured weekly and freezing tolerance was determined five times. Results showed that as seedlings acclimated to decreasing air temperature and photoperiod, stomatal conductance decreased linearly, photosynthesis was unchanged until air temperature and photoperiod were below 10°C and 11 h, respectively, water-use efficiency nearly doubled and freezing tolerance increased in a curvilinear fashion. There was significant between- and within-family clonal variation in all of these physiological parameters.