Within-ring variability of wood structure and its relationship to drought sensitivity in Norway spruce trunks

ABSTRACTRelationships between hydraulic vulnerability expressed as P50 (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 P50 relating to functional aspects. WD and tracheid dimensions were measured with SilviScan on Norway spruce (Picea abies (L.) Karst.) trunk wood.P50 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/bt)2) gave better results (r = -0.54) than radial lumen width (r = -0.31). The correlations of P50 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 P50 values of each specimen. Tightest correlations were found for (t/bt)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 P50, 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.

Dynamics of cavitation in a Douglas-fir tree-ring: transition-wood, the lord of the ring?

The objective of this work was to investigate the dynamics of embolism formation within a Douglas-fir tree-ring. Four resistant and four vulnerable 10-year-old trees were selected among 50 trees, based on their P50. Stem samples, taken next to those used to obtain the vulnerability to cavitation curves, were collected and submitted to increasing positive pressures, in order to simulate increasing tension caused by water stress in the xylem. Then the conductive surface of the samples was stained and scanned and the images were analyzed. X-ray microdensity profiles were obtained on the same samples. The microdensity profiles of the 2011 ring were analyzed in three parts, earlywood, transition-wood and latewood. The dynamics of embolism propagation was observed separately in these three parts. Our results showed that the initiation and the propagation of the cavitation follow a discrete trend, with at least two successive initiation events: first cavitation initiates and propagates rapidly in the latewood. Then, a second cavitation event begins and spreads in the earlywood and eventually propagates to the transition-wood, which remains the last conductive part in the ring before full embolism. We observed that resistant to cavitation trees showed lower transition-wood density than vulnerable to cavitation trees.

Comparative Analysis of two DNA Extraction Protocols from Fresh and Dried wood of Cunninghamia Lanceolata (Taxodiaceae)

DNA was isolated from the sapwood, transition wood and heartwood of fresh and dried Cunninghamia lanceolata wood using two DNA extraction protocols: the modified CTAB method and the modified Qiagen kit. Our major objective was to (i) determine an optimized method for retrieving good quality and sufficient quantity of DNA from wood, and to (ii) investigate the effect of different radial positions of fresh and dried wood for DNA extraction. In comparison with the modified CTAB method, a greater quantity of higher quality DNA – both chloroplast and nuclear ribosomal DNA – was retrieved using the Qiagen kit protocol. The chloroplast DNA regions retrieved from both fresh and dried wood were successfully amplified using both protocols, but the PCR amplification for the rDNA-ITS region from the heartwood failed using both protocols. The quantity and purity of the DNA from the sapwood and transition wood (derived from nuclei and plastids in the parenchyma cells) was greater than that from the heartwood (derived mainly from amyloplasts). Due to the influence of the drying treatment, the quantity of DNA decreased by more than 50%. The optimized radial position for DNA extraction in the stem was demonstrated based on anatomical observation.

Genetic variation in wood properties of interior spruce. II. Tracheid characteristics

In this study we investigated quantitative genetic variation in tracheid characteristics in two genetic tests of British Columbia's interior spruce (the common name for white spruce, Picea glauca (Moench) Voss; Engelmann spruce, Picea engelmanni Parry ex Engelm.; and their hybrids). The study included 88 half-sib families from the East Kootenay and Prince George regions. We have developed a technique for quantitative assessment of tracheid characteristics by measuring cross-sectional dimensions. We obtained cell size, wall thickness and their ratio in early-, transition-, and late-wood classes within a growth ring. Tracheid length and microfibril angle were measured in the transition wood. A number of tracheid characteristics showed significant genetic variation, but heritability, phenotypic, and genetic correlation estimates varied across test sites within and outside regions of origin of parental trees. Ring width was determined, both phenotypically and genetically, by the number of tracheids and to a lesser extent by the by their mean size. On average, rings with larger tracheids did not have significantly thicker walls. Wider rings had lower mean wall to tracheid size ratio. Faster growth did not result in shorter tracheids in the transition wood. Longer tracheids had lower micro fibril angle. There were no particular benefits from considering the anatomical component traits for breaking the negative genetic correlation between growth and wood density.

Variations in Transverse Fibre Wall Properties: Relations Between Elastic Properties and Structure

Summary The transverse mechanical properties of the wood fibre play important roles in the use of wood and its fibres in various applications. However, the variation in properties of fibres from different parts of the tree and the relation of these properties to the structure of the fibre is not yet established. This study focuses on the variation in the transverse elastic modulus of the fibre wall and its relation to the fibril structure of the S2- and S1-layer. For this reason the local fibril angle of radial and tangential fibre walls were measured by polarisation confocal microscopy. It was shown that the variation in fibril angle of the S2-layer seems to have very little influence on the transverse modulus of the fibres. Instead the thickness and fibril angle of the S1- and thus also the S3-layer should contribute to the variation in transverse modulus between earlywood and transition wood fibres. The importance of the ray cells for the transverse elastic properties of the wood was also emphasised.