Browsing by Author "Guo, Siying"

This thesis represents a thorough study on association between tree height and phloem anatomy of a tree. Phloem is one of the major components of the vascular system of a plant as it facilitates the transportation of products of photosynthesis from source to sink. In this research, a coniferous tree species, Picea abies (L.) Karst, which is commonly known as Norway spruce, was carefully examined as a model plant. Specifically, the correlation between tree height and the anatomical features of cells that constitute each compartment of a tree stem (i.e., outer bark, phloem, cambium, and xylem, which is composed of sapwood and heartwood) was investigated, aiming to help understand the phloem anatomy and elucidate the underlying mechanisms that govern the secondary tree growth. In particular, the variations of an array of anatomical properties of wood, such as cell number, cell size, structural dimensions, were measured at different height levels to establish the axial profiles for these anatomical features. Notably, the number of tracheid and sieve cells in the stem of Norway spruce was found to increase with tree height and water stress gradient. While the size of tracheid cell in radial direction exhibited no distinct axial pattern, a decrease in sieve cell size from the middle part of the living crown towards the top of the crown in both radial and tangential direction was observed. Also, the widths of wood layer, phloem and periderm exhibited dependence on tree height. This dissertation consists of a literature review relevant to this study, the detailed experimental methods involved in this work, a summary of the results and discussion, and a conclusion chapter.