The influence of thinning at age eight on the photosynthetic rate, needle conductance, xylem water potential, water use efficiency and growth of loblolly pine trees was studied during their ninth and tenth growing seasons. Litterfall dynamics were monitored throughout the study period as well. At the end of the second post-thinning growing season, trees in thinned plots had greater stem diameters, greater live crown ratios, greater live crown diameters and greater average volumes and basal areas than did trees in control plots. Significant physiological changes due to thinning were observed only in the lower crowns where needles were found to adapt to the sudden increase in available light by adjusting their physiology to resemble that of sun needles. Lower crown photosynthesis and needle conductance in thinned plots were more similar to upper crown values for these parameters than to lower crown, control plot values. Foliage produced during the current year and measured after full elongation had a higher average photosynthetic rate, needle conductance and lower average water potential than did foliage in its second growing season during both 1988 and 1989. Additionally, the water use efficiency of current-year foliage was significantly greater than that of the second-year foliage. In both thinned and control plots, significant diameter growth and photosynthesis continued throughout the dormant season although at a slower rate than during the growing season. Litterfall timing did not differ between thinned and control plots, nor did the amount of litterfall per unit basal area during the first year following thinning. Partial second-year data suggest that subsequent litterfall amounts will mirror the greater average crown size in thinned plots. / Master of Science

Empirical and theoretical relationships between tree crown, stem and stand characteristics for unthinned and thinned stands of planted loblolly pine were investigated. The individual tree crown measurements of crown diameter (CD) and crown projection area (CPA), and stand level measurement of the sum of crown projection areas (SCPA) were particularly important in contributing to high levels of model fit and prediction abilities of common stem and stand characteristics. As these crown measures developed over time so did corresponding stem and stand attributes. The results were similar for trees and stands located in unthinned or thinned situations; however, a limited range of data may have accounted for these similarities. The stem attributes modeled included basal area and diameter and associated growth, while the stand attributes modeled were basal area and mean dbh and associated growth. Models were also developed for the individual tree crown characteristics of CD and growth, CPA, and height to crown diameter, and for the stand level crown attributes of SCPA and growth, mean crown projection area and mean height to crown diameter. Several common competition indices were adapted to include crown information and various structural changes. The most effective competition measures in helping to predict basal area growth were point in time crown measures of SCPA and CD for trees located in unthinned stands and SCPA and CPA for trees located in thinned stands. Lastly, the effects of planting rectangularity on stem basal area growth were investigated. Two measures of rectangularity were calculated: one dealing with the ratio of distances between adjacent competing trees and another involving the ratio of the major and minor axis distances of a subject tree's crown diameter. Depending on the age of the stand,. these measures of rectangularity were found to be significant in negatively affecting stem basal area growth of trees located in unthinned stands. / Ph. D.

M.S.

Drought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.

No description available.

No description available.

No description available.

Drought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.

Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references (p.71-87).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1962. / Includes bibliographical references (p. 42-45).