Date of Award


Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)


Forest Resources


Michael E. Day

Second Committee Member

Michael S. Greenwood

Third Committee Member

Laura Kenefic


There are concrete morphological and physiological differences in foliage found among crown positions, tree ages, and needle ages in conifer trees. This study investigated the influence of crown position, needle age, and tree age on photosynthetic pigments and nitrogen. General trends showed that old trees (~155 years old) were associated with high nitrogen and pigment plasticity values in previous to current year needles and no crown position plasticity related to sun and shade environments. Conversely, juvenile trees (~25 years old) showed high plasticity values in shade-adapted compared to sun-adapted leaves and little year to year foliar plasticity. While previous studies have demonstrated that variation in needle morphology due to development of foliage in sun and shade light environments is consistent across tree age classes, these results suggest that photosynthetic pigments do not follow that pattern.

Sun-shade differences in needle morphology have been attributed to detection of light environment by the pigment phytochrome. However, the lack of response of pigment composition to environment found in this study suggest a different physiological mechanism is involved. An alternative explanation for this interaction of ontogenetic trends and environment in regulating sun/shade characteristics in pigment physiology is based on the phytohormone cytokinin. In this hypothesis increased branch junctions, length and complexity of transpiration stream result in less cytokinin availability within the whole canopies of old trees independent of light environment and are responsible for pigment regulation.

To test the influence of cytokinin on photosynthetic pigment concentrations in red spruce, we applied three levels of exogenous cytokinin treatments to old and juvenile foliage. The optimum concentration for exogenous cytokinin treatments were found to be 50mg L-1 to l00mg L-1, with 100 being optimal for pigment response. Needle count, bud count, bud length (cm), bud width (cm), stem mass (g), stem diameter (cm) and stem length (cm) increased with cytokinin treatment, typical of its action enhancing growth of plant tissue, but all pigments were suppressed. Cytokinin suppression of chlorophyll synthesis has been reported in herbaceous species, but not in woody plants. These data support the concept that foliar sun-shade adaptation in physiological processes differ from morphology and may result from ontogenetic differences in hydraulic architecture and regulation by phytohormones.