EFFECTS OF COLD-STORAGE AND WATER-STRESS ON WATER RELATIONS AND GAS-EXCHANGE OF WHITE SPRUCE (PICEA-GLAUCA) SEEDLINGS

To determine the effects of lifting time and storage on water-stress r esistance of nursery-grown white spruce (Picea glauca (Moench) Voss) s eedlings, we compared gas exchange, water relations and mortality of 3 -year-old seedlings lifted in October 1991 and stored at -2 degrees C for 3 months with seedlings lifted in January 1992. The seedlings were placed in nutrient solution and subjected to -1.1 or -2.7 MPa water s tress induced by polyethylene glycol 3350 for 9 days. Water stress, bu t not lifting time, had a significant effect on seedling net assimilat ion, symplastic volume and turgor loss point. In a second experiment, seedlings lifted in October 1991 were stored at -2 degrees C for 7 mon ths and compared with seedlings lifted in May 1992. The seedlings were planted in pots, and their gas exchange and water relation parameters measured in response to gradual water stress. The results suggest tha t prolonged cold storage retards photosynthetic recovery of seedlings after planting. Higher rates of net assimilation in seedlings lifted i n May were not directly related to their water status. Nonstomatal lim itations were the primary factor influencing photosynthetic rate. We c onclude that the inferior ability of cold-stored seedlings to tolerate water stress was due to poor osmotic adjustment and a lag in recovery of photosynthesis.