ABSTRACT

All cell types of the secondary xylem arise from the meristematic cells (initials) of the vascular cambium and grow under mechanical constraints emerging from the circular-symmetrical geometry that characterises many tree trunks. The course of intrusive growth of cambial initials has been elucidated, but is yet to be described in the case of xylem fibres. This study explains the geometry of intrusive growth of the secondary xylem fibres in the trunk of Robinia pseudoacacia. Long series of serial semi-thin sections of the vascular cambium and the differentiating secondary xylem were analysed. Since fibres grow in close vicinity to expanding cells of the derivatives of the vascular cambium, we assumed that they have similar growth conditions. Dealing with the cylindrical tissue of the vascular cambium in a previous study, we used a circularly symmetrical equation for describing the growth mechanism of cambial initials. Like the cambial initials, some of the cambial derivatives differentiating into the various cell types composing the secondary xylem also exhibit intrusive growth between the tangential walls of adjacent cells. As seen in cross sections of the cambium, intrusively growing initials form slanted walls by a gradual transformation of tangential (periclinal) walls into radial (anticlinal) walls. Similarly, the intrusive growth of xylem fibres manifests initially as slants, which are formed due to axial growth of the growing cell tips along the tangential walls of adjacent cells. During this process, the tangential walls of adjacent cells are partly separated and dislocated from the tangential plane. The final shape of xylem fibres, or that of vessel elements and axial parenchyma cells, depends upon the ratio of their intrusive versus symplastic growths in the axial, circumferential and radial directions.

In: IAWA Journal

ABSTRACT

A remarkable, almost fur-like “indumentum” of velvety “hairs” (sometimes referred to as “fungi”) occurs on the roots (and to a lesser extent also on the trunk) of Lannea schweinfurthii var. stuhlmannii and is known as vhulivhadza in the Venda language (Tshivenḓa). The hairs are traditionally used by the Venda people (Vhavenḓa) of the Limpopo Province of South Africa, for various biocultural purposes. A detailed anatomical study of the origin, structure and development of these unusual “hairs” showed that they are of peridermal origin and develop from dense clusters of phelloid cells which are scattered within the stratified phellem. These cells are capable of considerable radial elongation thus forming hair-like radial files of elongated phelloid cells. The “hairy” patches on the bark may also develop from lenticels which become hypertrophied. These clusters of phelloid cells resemble the hyperhydric tissue which is reportedly formed in periderm of stems exposed to a water-saturated environment in some plant species. The formation of hyperhydric-like tissue in roots and stems of L. schweinfurthii var. stuhlmannii occurs, however, under relatively arid conditions. Since this tissue contains large intercellular spaces, it may also be regarded as a specialized type of aerenchymatous phellem. The adaptive significance, if any, of the phelloid “hairs” remains unknown.

In: IAWA Journal

Abstract

In this study, the ice nucleation activity (INA) and ice nucleation temperature (INT) as well as extracellular ice formation within the bark were determined for three woody species with different degrees of frost resistance, Betula nana, Betula albosinensis and Castanea sativa. Current-year stems and at least 2-year old stems of B. nana and C. sativa as well as current-year stems of B. albosinensis were compared, during summer (non-acclimated state) and winter (acclimated state), to evaluate possible ontogenetic and seasonal differences. Acclimated plant parts of the selected species revealed nearly similar results, with an INT from -7.52 to -8.43°C. The current-year stems of B. nana had a somewhat higher INT than the older stems. Microscopic analysis showed that extra-cellular ice formation occurred in the intercellular spaces within the bark of stems of B. nana, B. albosinensis and C. sativa. Size of the intercellular spaces of the bark were species-specific, and B. nana showed the largest intercellular space volume. While freezing behavior and extracellular ice formation thus followed principally the same pattern in all considered species, B. nana is obviously capable of dealing with large masses of extracellular ice which accumulate over extended periods of frost, making B. nana capable of protecting living tissue in colder regions from freezing damage.

In: IAWA Journal

ABSTRACT

Projected changes in drought occurrence in the Mediterranean region are raising concerns about the adaptive capability of rainfed crops, such as grapevine, to increasing aridity. Cultivation management, especially the techniques influencing the hydraulic pathway, can play a role in plant adaptation to drought for the consequent changes in wood anatomical functional traits. The aim of this study was to assess the effect of grafting on wood anatomy in tree-ring series of Vitis vini-fera L. ‘Piedirosso’ grapevine cultivated in a volcanic area in Southern Italy. Tree-ring anatomy was analysed in vines grown on their own roots or grafted onto 420A rootstock. Results showed that grafted vines had a higher occurrence of wood traits linked with safety of water transport if compared with non-grafted vines. Grafting induced the formation of tree rings with higher incidence of latewood also characterised by narrower and more frequent vessels if compared with non-grafted vines. This study suggested a different regulation of water flow in the grafted and non-grafted vines. Such findings support the analysis of wood anatomy as a tool to drive decisions linked with plant cultivation management. In this specific case, our results encourage to further explore the change from a traditional cultivation with own-rooted grapevines towards grafted models inducing better xylem adaptation to increasing drought.

In: IAWA Journal

ABSTRACT

Phytophthora austrocedri is a straminipilous (heterokonta) organism that causes mortality of Austrocedrus chilensis, an endemic Cupressaceae from the Patagonian Andes forest in temperate South America. This soil pathogen colonizes and kills the roots and extends up to the stem causing necrosis of cambium, phloem and xylem ray parenchyma. An anatomical study of affected tissues was conducted in order to better understand the process of pathogen colonization and tree response. It was found that tracheids of the xylem of affected trees showed large numbers of trabeculae, both rod- and plate-shaped. The occurrence of these structures was clearly associated with the necrotic lesion area, since the trabeculae were rare in healthy tissues above the necrotic lesion. Trabeculae occurred in a variety of arrangements: solitary or in long files, single, double or triple. Our results could indicate that trabeculae proliferation in tracheids of A. chilensis trees is induced by the stress generated by the P. austrocedri invasion. Whether this is triggered by a nonspecific stress response or in direct response to the pathogen remains to be tested.

In: IAWA Journal

Identification of archaeological or soil charcoal in a species-rich biome, such as the Central African rainforest, is challenging because of the large number of woody taxa with similar and overlapping wood anatomical features. Valid environmental or archaeological interpretations can only derive from reliable and transparent identifications that allow comparison of and referencing between different charcoal assemblages. The identification of 30 archaeological charcoal types from the site Dibamba in southern Cameroon serves as a starting point for a discussion on classification and naming. These 30 types are fully documented and illustrated in the Supplementary Online Material (SOM). The discussion underlines the basics of “good practice” of charcoal identification in a speciesrich tropical environment. The value of differential diagnosis is stressed, as is the importance of leaving identification levels on higher taxonomic level if necessary. We argue that the level of identification must be reflected in the name of the charcoal type. Names of charcoal types are written in small capitals to clearly distinguish them from botanical taxa with which they are not necessarily identical. The Dibamba charcoal assemblage offers the first and so far unique possibility to directly comprehend human impact on the structure and composition of West Central African rainforest over the last 3000 years. The paleoenvironmental significance of the results presented here will be subject of a forthcoming publication.

In: IAWA Journal

The first reports of a dead forest on Trindade Island are from the 18th century. Since then, the tentative identifications of the trees with red wood included Caesalpinia, Acacia, Rapanea, Pisonia, Eugenia and Colubrina, the latter having been confirmed by three independent wood anatomists familiar with Brazilian woods. In the 1960s Johann Becker was the last to sample a live Colubrina glandulosa Perkins var. reitzii on Trindade, which was presumed to be a remnant of the extinct forest. Based on this information, along with the eradication of feral goats from the island in 2005, thousands of C. glandulosa seedlings were reintroduced to Trindade. These trees, which grew well at first, are now collectively dying, less than two decades after planting. Their wood colour is much lighter than that of the dead trees, raising doubts about the latter’s correct identification. Herein we report the first detailed descriptions of two wood types from the extinct forest of Trindade, confirming the presence of C. glandulosa and reporting the presence of Paratecoma peroba (Bignoniaceae), a novel occurrence for the island. Radiocarbon dating of a dead C. glandulosa tree confirms that it belongs to the forest which died three centuries ago. The preserved wood proves that the extinct forest was not monospecific and suggests that further sampling of the remaining dead wood may enhance the floristic knowledge of the forest which once covered most of the island with additional species.

In: IAWA Journal