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UBC Theses and Dissertations

Cambial and photosynthetic activity relations in untreated, wounded, and geotropically stressed white spruce (Picea glauca (Moench.) Voss) seedlings Falls, Robert William


This thesis reports results of a study of relationships between photosynthetic activity and developmental parameters, and cambial activity (wood formation rate), during and following the period of active wood formation in untreated white spruce seedlings, and in seedlings stressed either by extensive stem incisions, or by tilting. The approach involved the use of two non-destructive methods for measuring photosynthetic activity: chlorophyll a fluorescence using optical instrumentation, and CO₂ uptake using infrared gas exchange techniques. Photosynthetic development was examined by estimating chlorophyll a content from a specific fluorescence parameter (O-level), and by the relative occurence of specific chloroplast stroma and membrane (thylakoid) proteins using electrophoretic and immunoblotting techniques. Cambial activity was determined using digitized image analysis of prepared cross-sections of seedling stems. Several fluorescence parameters were strongly correlated to cambial activity in untreated seedlings during the period of active wood formation (in mid-summer). However, the correlations were severely diminished or non-existent when cambial activity was arrested (in late-summer and autumn). Correlations between fluorescence and cambial activity in stressed seedlings were not discernible at any time, suggesting that the induced stresses resulted in a substantial alteration in normal source:sink relationships. Carbon dioxide uptake measures, either uncorrected or corrected to estimated chlorophyll α content, were not measurably correlated to cambial activity in untreated or stressed seedlings at any time in this system. Chlorophyll α content estimated from O-level fluoresecence, was not related to cambial activity in untreated or stressed seedlings. The relative occurences of two enzymes and proteins associated with photosynthetic carbon fixation, i.e. ribulose 1,5-bisphosphate carboxylase (Rubisco) and Coupling Factor, did not appear to be influenced by applied wounding and geotropic stresses. In contrast to the strong correlations found between fluorescence parameters and current season stem vigour, pre-season seedling height and cross-sectional stem areas were not related to stem vigour. These results suggest that in unstressed white spruce seedlings, the measure of specific chlorophyll α fluorescence parameters, using the methods delineated in this study, offers an alternative and more strongly predictive means of assessing current stem vigour, than measures of seedling dimensions. The results of this study provide strong evidence for, and a degree of elucidation on, the anticipated but previously unestablished existence of a source:sink relationship between leaves and vascular cambium in conifer seedlings. This information should provide an initial foundation for the elucidation of non-invasive methodologies by which to assess stem vigour of white spruce seedlings, and to probe source:sink relationships in other conifer species.

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