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Author: Sabine Rosner

Secondary xylem (wood) fulfills many of the functions required for tree survival, such as transport of water and nutrients, storage of water and assimilates, and mechanical support. The evolutionary process has optimized tree structure to maximize survival of the species, but has not necessarily optimized the wood properties needed for lumber. Under the impact of global warming, knowledge about structure-function relationships in tree trunks will become more and more important in order to prognosticate survival prospects of a species, individuals or provenances. Increasing our knowledge on functional wood anatomy can also provide valuable input for the development of reliable, fast, and at best quasi-non-destructive (e.g. wood coring of mature trunks) indirect screening techniques for drought susceptibility of woody species. This review gives an interdisciplinary update of our present knowledge on hydraulic and biomechanical determinants of wood structure within and among trunks of Norway spruce (Picea abies (L.) Karst.), which is one of Europe’s economically most important forest tree species. It summarizes what we know so far on 1) withinring variability of hydraulic and mechanical properties, 2) structure-function relationships in mature wood, 3) mechanical and hydraulic demands and their tradeoffs along tree trunks, and 4) the quite complex wood structure of the young trunk associated with mechanical demands of a small tree. Due to its interdisciplinary nature this review is addressed to physiologists, foresters, tree breeders and wood technologists.

Free access
In: IAWA Journal

Seasonal production of lenticel tissues was compared between Norway spruce trees (Picea abies (L.) Karst.) from a mountain site (1200 m), where they are autochthonous, and seven allochthonous lowland sites (250–600 m).

The periodic changes of lenticel structure were grouped into four stages, based on the degree of their opening: phase 1 - winter dormancy; phase 2 - beginning of meristem activity in spring; phase 3 - production of non-suberised filling tissue in early summer, which causes the disruption of the closing layer formed in the previous growing season; and phase 4 - differentiation of a new closing layer in late summer. Structural changes in lenticels of P. abies may be interpreted as a long-term reaction to climatic conditions, balancing transpiration and respiration. During the most active period of wood production, lenticels were found in their most permeable phase, phase 3. The production of a new closing layer takes place when summer temperatures reach maximum values, and when demand for effective regulation of transpiration is high. During phase 4 transpiration is successfully controlled because differentiating cells of the new closing layer are already suberised, although not in their final rounded shape, and therefore have small intercellular spaces. High annual variability in stratification of lenticel tissues, such as the proportion between closing layer and filling tissue, wall thickening and size of intercellular spaces, also indicates possible long-term regulation mechanisms for transpiration.

Free access
In: IAWA Journal
Authors: Sabine Rosner and Hugh Morris

Summary

Lenticels can be defined as pores that are the entrance of a continuous aeration system from the atmosphere via the living bark to the secondary xylem in the otherwise protective layers of the periderm. Most work on lenticels has had an anatomical focus but the structure-function relationships of lenticels still remain poorly understood. Gas exchange has been considered the main function of lenticels, analogous to the stomata in leaves. In this perspective review, we introduce novel ideas pertaining to lenticel functions beyond gas exchange. We review studies on lenticel structure, as this knowledge can give information about structure-function relationships. The number of species investigated to-date is low and we provide suggestions for staining techniques for easy categorization of lenticel types. In the follow-up sections we review and bring together new hypotheses on lenticel functioning in the daily “normal operation range”, including regulative mechanisms for gas exchange and crack prevention, the “stress operation range” comprising flooding, drought and recovery from drought and the “emergency operation range”, which includes infestation by insects and pathogens, wounding and bending. We conclude that the significance of dermal tissues and particularly of lenticels for tree survival has so far been overlooked. This review aims to establish a new research discipline called “Phytodermatology”, which will help to fill knowledge gaps regarding tree survival by linking quantitative and qualitative lenticel anatomy to tree hydraulics and biomechanics. A first step into this direction will be to screen more species from a great diversity of biomes for their lenticel structure.

In: IAWA Journal

ABSTRACT

Relationships between hydraulic vulnerability expressed as P 50 (the air pressure causing 50% loss of hydraulic conductivity) and within-ring differences in wood density (WD) and anatomical features were investigated with the aim to find efficient proxies for P 50 relating to functional aspects. WD and tracheid dimensions were measured with SilviScan on Norway spruce (Picea abies (L.) Karst.) trunk wood.

P 50 was strongly related to mean WD (r = -0.64) and conduit wall reinforcement ((t/b)2), the square of the ratio between the tracheid double wall thickness (t) and the lumen width (b), where use of tangential lumen width ((t/b t)2) gave better results (r = -0.54) than radial lumen width (r = -0.31). The correlations of P 50 with earlywood (EW), transition wood (TW) and latewood (LW) traits were lower than with the specimen averages, both for WD (r = -0.60 for WDEW, r = -0.56 for WDTW, r = -0.23 for WDLW) and all anatomical traits. The loss of hydraulic conductivity was addressed as a dynamic process and was simulated by defining consecutive phases of 5% theoretical conductivity loss. WD and tracheid traits were calculated and correlated with P 50 values of each specimen. Tightest correlations were found for (t/b t)2, at relative cumulated theoretical conductivities until 45 to 50% (r = -0.75).

We conclude that WD is one of the best available proxies for P 50, but does not necessarily reflect the mechanism behind resistance to cavitation. The new trait, based on estimation of conductivity loss as a dynamic process, provided even stronger correlations.

In: IAWA Journal