The anatomy and functioning of stem secondary xylem in relation to the decline of European ash (Fraxinus excelsior L.) was examined and the hypothesis that declining trees show changes in the structure of wood, resulting in impaired water transport was tested. Anatomical analyses were carried out on samples comprising annual rings formed between 1970 and 2009 and collected at the breast height of the main stem of fifteen trees 40−90 years old. Trees were based upon health condition and classified as healthy, weakened or dead. Tree−ring widths as well as diameter and density of earlywood vessels were measured and the theoretical hydraulic conductivity index through the secondary xylem calculated by application of Hagen−Poisseuille formula. Over the whole investigated period the smallest early vessels were attribute to ashes dead at the time of sampling. In the period when dieback symptoms where manifested in the stand, the diminishment of vessels diameter occurred in weakened and eventually dead trees, whereas healthy trees produced even slightly larger vessels than before. Having large vessels implies that healthy trees were able to keep high hydraulic conductivity index, whereas trees in decline at this time produce smaller vessels and hence had reduced conductivity in respect to previous.
This paper reviews the structure and formation of periderm and rhytidome in organs both of coniferous and broadleaves trees, in respect to their protective role. The periderm, which is composed of three tissues such as meristematic phellogen giving rise to suberized phellem at the outer side and phelloderm at the inner side. In older organs peridem is replaced with rhytidome composed of dead cells and included subsequent periderms separated by functioning phloem cells. Additionally, the structure and classification of lenticel as well as development of cork wings is described.
The paper describes the different types of cell death during the process of wood cell formation and terminological variety found in the literature concerned. The cell death referred to as programmed cell death (PCD), is genetically controlled and fundamental for the correct function of the whole organism of woody plants. The wood is mainly composed of the tracheary elements fulfil as conductors of water, fibers that provide the mechanical support and parenchyma cells playing an important role in the storage of water and reserve materials. The PCD of these elements constitutes the final stage of their differentiation and it is proceeded by: (i) cambial cell divisions, (ii) the enlargement of the cambial derivatives. The successive phase concerns (iii) deposition of secondary cell walls and its lignification. After that, the cell commences to digest protoplast, what means that each cell participates in the process of its own demise actively. However, the time and the sequence of the appearance of these phases are distinct among the woody cells. In the case of the tracheary elements the digestion of the protoplast occurs immediately after the tonoplast breakdown. Therefore, these cells are short−lived elements of wood. The life span of the fibers and the parenchyma cells is longer (from month for fibers and years in case of parenchyma cells). For the latter cells the positional information (distance from the cambium) and vicinity with short−lived tracheary elements are considered to be important for undergoing the process of death
The trade−off in case of water transport is captured in ecological theory by the safety vs. efficiency concept. As the efficiency of transport of water depends mainly on the dimensions of the conductive elements in wood, this paper presents the survey on some methods that allow to quantify the tracheids and vessels attributes including their diameter (tangential/radial, hydraulic), length as well as arrangement (axial, radial). Each trait of conductive elements is briefly described and formula for its calculation is given. Moreover, the usefulness of measurable traits for calculating the meso− and xeromorphy index is presented. Given the fact that the structure of pits and complexity of perforation plate (scalariform, ladder−like) are important factors in wood hydraulic resistance, the following parameters were additionally characterized: the pit membrane diameter, pit membrane thickness, pit chamber depth and the number of bars per perforation plate between the adjacent vessel elements.
This paper reviews the literature on heartwood and its formation process. The factors involved in the process of heartwood formation are described, with particular attention paid to molecular, intercellular, organismal and environmental ones. The spatial distribution of heartwood along longitudinal and radial axes of the stem as well as biochemical changes in the heartwood and durability of this zone are also presented. Based on the literature data, it turns out that the heartwood formation is neither clearly studied, nor fully understood. It seems that this part of wood can not only play a significant role from the point of view of tree biomechanics, but also is of great importance in their immune responses. In the era of observed dying processes of forest−forming trees, knowledge about the role of heartwood in these responses seems desirable.