Denis P. Lavender

Spring shoot growth in douglas-fir may be initiated by gibberellins exported from the roots.

Trials conducted under controlled environments demonstrated that the delay of bud activity of Douglas-fir (Pseudotsuga menziesii) seedlings occasioned by low temperature of the soil could be eliminated by application of gibberellic acid. Analyses of field-grown plants showed a parallel increase in bud activity, level of gibberellin-like compounds in xylem sap, and soil temperature during February and March.

Plant Physiology and Nursery Environment: Interactions Affecting Seedling Growth

Environmental factors (such as light, moisture, nutrients, density, and temperature) and plant physiological factors (such as carbohydrate reserves, hormone levels, frost hardiness, and dormancy) interact to shape growth and survival of coniferous seedlings in nursery fields and after outplanting. Nursery managers can manipulate moisture, nutrients, and density to achieve desired seedling morphology and vigor. However, the annual growth cycle of perennial plants has evolved in response to environmental pressures. When the environment is modified, as with heavy irrigation in a nursery, to permit growth at a time when natural seedlings are dormant, the ensuing phases of the growth cycle will not be properly synchronized with their environments. Seedlings so cultivated lack vigor after outplanting. Nursery managers should aim at keying their cultivation schedules to both environmental conditions and endogenous seedling physiology toensure production of high-quality seedlings.

Effect of Environment on the Development of Dormancy and Growth of Douglas-Fir Seedlings

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) first-year seedlings from seeds collected from stands in central British Columbia and different altitudes in Oregon were grown under a series of artificial environments for 4 months in each of 3 years. Vegetative growth of seedlings from all seed sources was-stimulated by long (15 hr) photoperiods, high (21 C) night temperatures, and moist soil. Early dormancy was induced by short (9 hr) photoperiods, low (3 C) night temperatures, and dry soil.

Urea fertilization and foliar nutrient composition of western hemlock (Tsuga heterophylla (Raf.) Sarc.)

Abstract Foliar mineral contents of hemlock stands in coastal and Cascade Mountain zones of the Pacific Northwest were studied to determine the effect of urea fertilization on foliar nutrients. The results demonstrate that mineral concentrations vary among foliage age classes, stands, and zones. Concentrations of N, P, K, Ca, Mg, Al, Mn, Fe, Cu, Zn and B were significantly higher in the Cascade Mountain stands than in the coastal stands. Urea fertilization significantly increased the N content in all age classes of foliage but reduced the concentrations of P, Ca, Mg, Mn, Fe, Al and B, especially in coastal stands. The poor response of coastal stands to urea fertilization, therefore, is probably due to further reduction in already low foliar levels of essential nutrients other than N.