Graduate Thesis Or Dissertation
 

Effects of light preconditioning on the seasonal water relations of nursery-grown Douglas-fir

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  • Douglas-fir seedlings of a single seed source were grown in a nursery under three levels of light intensity: 9, 44, and 100 percent of full light. Growth over an entire growing season was monitored in terms of proportionate distribution of dry matter to shoot and root systems. This was replicated over two years, 1971 and 1972, with the subsequent effects of prior light treatment upon growth and phenology noted as well as current effects of first-year growth upon seedling water relations. Water relations analysis was based on the model, Plant Moisture Stress = f (Soil Moisture Stress, Leaf Conductance) and data subdivided as to summer, fall, and winter according to differing physiological states of the seedlings. By means of analysis of variance applied to regression models, effects of season of the year and light preconditioning upon water relations were demonstrated. These were attributed to differing influences of soil moisture stress and leaf conductance upon plant moisture stress Water relations analysis indicated that plant moisture stress of seedlings during active shoot growth is lower than after growth bas ceased. Decreased water Loss in the winter associated with low air temperatures was due to closure of stomata partially independent of moisture stress in the plant. Plant moisture stress was lower in seedlings during the winter than it was during fall at equivalent levels of soil moisture stress. Low light-preconditioned seedlings possess limited ability to avoid internal desiccation, probably due to a poorly-developed root system relative to their shoot. They are also more subject to spring frost damage. Indications are that low light. Preconditioning of seedlings’ growth the first year may have carry-over effect upon water relations behavior a year later. Light preconditioning has practical implicatior8 for forest nursery management through regulation of dormancy and morphology.
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