INFLUENCE OF DORMANCY INDUCTION TREATMENTS ON WESTERN HEMLOCK SEEDLINGS .1. SEEDLING DEVELOPMENT AND STOCK QUALITY ASSESSMENT

Western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedling were grown in a greenhouse and subjected to four dormancy induction treatments (DIT) (i.e., long-day dry, long-day wet, short-day dry, and short-day wet) during mid-summer. In the late summer and fall, seedling development was monitored and it was found that (1) short-day DIT caused a rapid cessation of shoot growth; (2) short-day DIT caused rapid fall development of needle primordia, while long-day DIT took until midwinter to produce the same number of needle primordia; and (3) short-day DIT seedling had lower saturated and turgor loss point osmotic potentials and greater maximum modulus of elasticity in October than long-day DIT. Seedlings were tested with a comprehensive stock quality assessment procedure just before late winter field planting. These tests showed the following: (1) morphological parameters: short-day DIT reduced shoot to root ratios; (2) pressure-volume analysis: short-day wet seedling had the lowest osmotic potential at saturation and turgor loss point; (3) soluble sugar analysis: greater levels of total soluble sugars were found in non water stressed DIT compared with water stressed DIT seedlings; (4) seedling water movement: short-day DIT seedlings had the lowest resistance to water movement at low root temperature (5-degrees-C); (5) low root temperature response: short-day compared with long-day DIT seedling had greater photosynthesis and stomatal conductance at low root temperatures; (6) root growth capacity: seedling from all DIT were capable of growing roots at optimum root temperature (22-degrees-C), but short-day compared with long-day DIT had greater root growth at low root temperatures; (7) drought stress response: short-day wet seedling had the highest photosynthesis and stomatal conductance levels as predawn shoot water potentials decreased; and (8) frost hardiness: short-day wet seedling had the least needle damage when tested at temperatures of -15 and -18-degrees-C.