The spatial structure of white spruce populations was studied in 52 stands. White spruce tree density increased with age in the 200-year chronosequence after fire. Tree height and DBH peaked at about 120 years after fire. Sapling density along the chronosequence after clearcutting exhibited similar pattern to that after fire, but peaked earlier. White spruce seedlings were present in various densities and heights along the chronosequence after fire, producing uneven-aged stands. Seedling regeneration was mostly on the LFH layer (72%) in younger plots and on logs (97%) in old plots. Seedlings in both regeneration types were evenly spaced at a young age. This pattern changed to random and clumped in older stands. Artificially planted clearcuts formed more even-aged stands. Physiological, morphological and growth responses to sun and shade treatments in the greenhouse were examined in white spruce seedlings collected from three naturally-regenerated (N1, N2 and N3) and three field-planted (P1, P2, and P3) stands. Dark respiration and light compensation points declined by 70 and 81% respectively, in shade- compared to sun-acclimated seedlings. Quantum yield, total chlorophyll content, specific leaf area and absolute water content increased by 45, 33, 32 and 50% respectively, in response to shade treatment. Height was not affected by light regime. Fewer and longer secondary branches were noticed in the shade compared to full sun. At light saturation, populations P1 and N3 showed similar photosynthetic responses under both light regimes (around 6 [mu]mol m-2 s-1). Populations P2, P3 and N2 performed more poorly in the sun than in the shade (8.2, 8.7 and 9.1 in shade, versus 5.1, 4.1 and 5.5 in full sun, respectively). Photosynthetic rate in N1 was greater in full sun than in shade (14.7 and 11.1 [mu]mol m -2 s-1, respectively). Differences in physiological responses to light among populations suggest the presence of more than one ecotype. The variation in physiological and morphological parameters within field-planted and naturally-regenerated populations was large, and did not show any obvious differences among populations. RAPD analysis showed abundant polymorphism in all populations. The naturally-regenerated arid the field-planted populations demonstrated similar within and among regeneration-type variation. Of the total genetic variation 82.9% was due to intra-population variation, while inter-population variation and regeneration type accounted for 16.7 and 0.4% of the total variation, respectively. It appears that selection pressure during reforestation was not great enough to cause a significant decline in the genetic diversity of field-planted compared to naturally-regenerated white spruce.

<p> In this thesis, the postglacial spread of three ecologically distinct species, Picea mariana (black spruce), Picea glauca (white spruce), and Pinus banksiana (jack pine), across the western interior of Canada are presented. The fossil pollen records from the sediments of thirteen lakes are used in reconstructing the population expansions of the three tree taxa. The objectives of this study are to examine temporal and spatial patterns in the growth of the populations and to determine if intraspecific and interspecific variations exist across a range of latitudes and elevations.</p> <p> Pollen accumulation rates (PAR) are calculated from pollen grain counts and sedimentation rates throughout the early-to mid-Holocene, and are used to represent the population level at the time of pollen deposition. Exponential equations are used to calculate population growth rates. Three dimensional diagrams (time, space, abundance) are constructed to illustrate the spread of the populations.</p> <p> The rates of population growth varied from south to north for all three species. Jack pine, on average had slower population growth rates, and its expansion across the region began over 3,000 years later than, and lasted approximately 1,000 years longer than the two spruce species. All three tree taxa experienced reduced rates of population growth at high elevation sites in the north. These variations are examined in light of the changing and static physical and botanical environmental conditions occurring during expansion.</p> / Thesis / Master of Science (MSc)

This research assesses whether a refinement of the temporal resolution of tree-ring data can improve our understanding of the radial growth-climate relationship. Two study sites in Northern Labrador were chosen, one coastal (Nain), and the other inland (Kamestastin). In Nain, microcore samples were taken weekly from the same five white spruce (Picea glauca) trees over the 2014 growing season. After cross sections were made and stained, the resulting 10µm thin radii provided a direct view of active ring development. In coastal Labrador, radial growth was initiated during the last week of June 2014, and ceased by August 25th. Circumference band dendrometers were installed on white spruce trees at both the Nain and Kamestastin sites. The dendrometers were used to measure micrometre-scale changes over the 2014 growing season. Analogous records of temperature were collected with equal temporal resolution, from an Environment Canada climate station (#8502800), and via a programmable data logger (UX120-006M, Onset HOBO). Correlation function analysis determined the relationship between daily temperature variables and daily variations in stem size. A strong relationship was found between minimum daily temperature and daily stem size at both sites over the eight week long growing season. Traditional dendrochronological sampling methods were utilized to retrieve tree cores from white spruce and eastern larch (Larix laricina) in Nain and Kamestastin. Site-specific master growth chronologies were created using crossdating and standardization techniques. After establishing long term records of monthly temperature and accumulated growing degree-days (GDD) at both study sites, a linear regression analysis was undertaken to determine the suitability of these two variables as predictors of annual-radial growth. An accumulated June/July GDD index was identified as an overall better predictor of annual ring-width than mean monthly temperature variables in northern Labrador. Exploring radial growth on an intra-annual scale helped to improve our understanding of the complex radial growth-climate relationship in Labrador. This allows for a strengthening of tree rings as a proxy climate indicator in remote regions of the northern boreal forest. The findings from this thesis provide the tools necessary to improve upon long-term climate reconstruction and forecasts of boreal forest structure in the face of climate change.

We examined the radial growth - climate association of a disjunct population of white spruce (Picea glauca (Moench) Voss) at its southern limit of distribution. Forty-four white spruce tree islands were sampled over four mixed-grass prairie preserves in the Spruce Woods Provincial Park located in the forestprairie boundary of southwestern Manitoba. Reduced radial growth occurred during the 1910s, 1930s, early 1960s, and the late 1970s to the early 1980s and corresponded to periods of drought on the Canadian prairies, and the Great Plains of the United States. Correlation and response function coefficients indicated that conditions in the summer and fall of the previous year (t-1), and the summer of the current year (t) strongly influenced white spruce growth. Growth was positively correlated with August-September (t-1) and May-June-July (t) precipitation and moisture index (precipitation minus potential evapotranspiration). Radial growth was positively associated with June-July-August (t) river discharge. Growth was most correlated with maximum and mean temperature compared with minimum temperature. Precipitation and maximum temperature accounted for the greatest variation in radial growth (61%). The results suggest that white spruce growth is sensitive to climatic fluctuations because growth is restricted by moisture deficiency exacerbated by temperature-induced drought stress.

The composition of lignin in the outer cell-wall layers of spruce and poplar has been studied and the data obtained have been compared with those of the mature reference wood in which the secondary cell wall predominates. Materials with exclusively or predominantly outer cell-wall layers were examined. Accurate data relating to the lignin monomer composition and the number of β-O-4´ bonds were obtained from pure middle lamella/primary cell wall lignin. Firstly, a 10 000 year old white spruce material, with most of the secondary cell wall missing, was studied. The aged lignin was composed of guaiacyl units only, and was slightly more condensed but otherwise similar to the reference lignin. Secondly, the developing xylem of a Norway spruce clone was analyzed during a growth season. In spring and early summer, growth is very rapid and the intention was to sample tissues in which the secondary cell-wall layers had not yet lignified, but where the outer layers at least had started to lignify. Microscopy, Klason lignin and carbohydrate analyses showed that the lignin in the developing xylem of samples from mid-June was located exclusively in the middle lamella. The lignin was more condensed, was composed of guaiacyl units only and contained more end-groups than the reference Norway spruce wood. Thirdly, the cambial tissues of a Balsam poplar clone were surveyed during a growth season. Both the phloem side and the xylem side of the cambial region were examined. The Klason lignin content and carbohydrate monomer distribution showed that in June and August the tissues on the phloem side contained material with mainly middle lamella/primary walls. In June, the xylem side in the cambial region contained mainly middle lamella/primary walls, and in August the secondary cell wall carbohydrates were being deposited. Both tissues contained lignin that was more condensed and had more end-groups than the reference lignin. In mid-June, the developing xylem had a ratio of syringyl to guaiacyl units of 0.6, whereas the ratio for the reference wood was 1.3. In the final study, lignin from the primary cell walls from a hybrid aspen cell suspension culture was investigated. The lignin contained only guaiacyl units which were more condensed than those observed in the reference poplar wood. / <p>QC 20100920</p>

The Arabidopsis chitinase-like1 (Atctl1) mutant, pom1 is compromised in primary cell wall development, resulting in short roots when grown on high sucrose and shortened hypocotyls when grown in darkness. To better understand this phenotype and the evolution of AtCTL1 and its homologue, AtCTL2, we obtained a large number of CTL sequences and determined the phylogenetic relationships among them. Since microarray analysis had suggested a change in auxin response or homeostasis in pom1, I used the auxin reporter DR5::GUS in the pom1 background to assess changes in distribution. To assess whether the biochemical functions of AtCTL1 homologues in Arabidopsis and other plants are conserved, I transformed pom1 with AtCTL2 and CTLs from poplar (Populus trichocarpa x Populus deltoides clone H-11) and from Picea glauca (spruce) and assessed rescue of the pom1 phenotype. To further understand CTL expression and function, Arabidopsis and poplar CTL promoter::GUS fusions were also expressed in Arabidopsis, PopCTL1 overexpressed in Arabidopsis, and CTL expression down regulated in poplar by RNAi. Our results indicate that CTL genes represent an ancient family encoding proteins of conserved biochemical function. In dicots, represented by Arabidopsis and poplar) duplicated CTL genes are differentially expressed in conjunction with primary and secondary cell wall development, respectively. Mutation of these genes results in improperly formed primary walls in certain cell types in the case of AtCTL1, and an impairment in the differentiation of vascular bundles for AtCTL2. Overexpression of PopCTL1 in Arabidopsis seems to over stimulate the differentiation of vascular bundles, and our studies show that auxin distribution is altered in the Atctl1 mutant. Down regulation of PopCTL1 and PopCTL2 in poplar appears to phenocopy aspects of these mutations, resulting in secondary cell walls that appear to have less deposition of lignin and an accelerated production of secondary xylem respectively. While specific biochemical function(s) of CTL genes were not studied, potential functions are discussed.

The Arabidopsis chitinase-like1 (Atctl1) mutant, pom1 is compromised in primary cell wall development, resulting in short roots when grown on high sucrose and shortened hypocotyls when grown in darkness. To better understand this phenotype and the evolution of AtCTL1 and its homologue, AtCTL2, we obtained a large number of CTL sequences and determined the phylogenetic relationships among them. Since microarray analysis had suggested a change in auxin response or homeostasis in pom1, I used the auxin reporter DR5::GUS in the pom1 background to assess changes in distribution. To assess whether the biochemical functions of AtCTL1 homologues in Arabidopsis and other plants are conserved, I transformed pom1 with AtCTL2 and CTLs from poplar (Populus trichocarpa x Populus deltoides clone H-11) and from Picea glauca (spruce) and assessed rescue of the pom1 phenotype. To further understand CTL expression and function, Arabidopsis and poplar CTL promoter::GUS fusions were also expressed in Arabidopsis, PopCTL1 overexpressed in Arabidopsis, and CTL expression down regulated in poplar by RNAi. Our results indicate that CTL genes represent an ancient family encoding proteins of conserved biochemical function. In dicots, represented by Arabidopsis and poplar) duplicated CTL genes are differentially expressed in conjunction with primary and secondary cell wall development, respectively. Mutation of these genes results in improperly formed primary walls in certain cell types in the case of AtCTL1, and an impairment in the differentiation of vascular bundles for AtCTL2. Overexpression of PopCTL1 in Arabidopsis seems to over stimulate the differentiation of vascular bundles, and our studies show that auxin distribution is altered in the Atctl1 mutant. Down regulation of PopCTL1 and PopCTL2 in poplar appears to phenocopy aspects of these mutations, resulting in secondary cell walls that appear to have less deposition of lignin and an accelerated production of secondary xylem respectively. While specific biochemical function(s) of CTL genes were not studied, potential functions are discussed.