Low temperature effects on physiological characteristics of dormant white spruce (Picea glauca) bareroot seedlings

The effects of low temperature storage on spring-lifted and fall-lifted white spruce (Picea glauca (Moench) Voss) bareroot seedlings were studied. Seedlings grown in the nursery beds photosynthesized in early spring. This photosynthesis resulted in a drastic increase in carbohydrate levels in both needles and roots before spring lifting. The carbohydrate levels were positively correlated with new root growth of seedlings planted in the forest and with terminal shoot growth in the second year following planting. The recovery of photosynthesis was accompanied by changes in the composition of soluble carbohydrates. These changes included an increase in sucrose and a decrease in raffinose and monosaccharides. Spring changes in seedling physiology also included decreases in cell wall elasticity, osmotic potential and relative water content at turgor loss point followed by an increase in osmotic potential and relative water content at turgor loss point shortly before bud break.; Spring-lifted seedlings could be stored at −2°C and +4°C for a limited time without negative effects on their physiology. The duration of safe storage depended on seedling physiological status at lifting time. The maximum recommended storage duration was 9 weeks. Seedlings stored for longer than 9 weeks showed bud flushing or terminal bud injury in storage and poor survival and reduced shoot growth after planting. Storage temperature did not significantly affect seedling total non-structural carbohydrate levels. However, −2°C storage resulted in an increase in sugar levels in needles and roots while 4°C storage maintained similar sugar levels to those before storage. Root growth potential declined with the duration of −2°C storage, but in 4°C storage, high root growth potential was maintained for 6, 9 and 3 weeks in seedlings lifted on April 20, April 27 and May 4, respectively.; Fall-lifted seedlings could be safely stored at temperatures lower than −2°C. However, lowering storage temperature did not significantly affect tissue carbohydrate levels. Storage temperature affected seedling water relations, gas exchange, bud dormancy release and root growth potentials. Lower storage temperatures resulted in higher osmotic adjustment, decreased cell wall elasticity and delayed bud flushing following planting. At −6°C storage, higher electrolyte leakage was measured in shoots and roots, and seedlings had lower root growth potential compared with those at −2°C and −4°C. Seedlings stored at −4°C had superior stress resistance characteristics including relatively low osmotic potentials at turgor loss point and at full saturation, rigid cell walls, high carbohydrate content and high root growth potential.