Mechanical Properties Of Individual Southern Pine Fibers. Part II. Comparison Of Earlywood And Latewood Fibers With Respect To Tree Height And Juvenility

This paper reports variations in mechanical properties of individual southern pine fibers and compares engineering properties of earlywood and latewood tracheids with respect to tree height and juvenility. Results indicate that latewood fibers exhibit greater strength and stiffness than earlywood fibers irrespective of tree height or juvenility. Average earlywood loblolly pine fibers had modulus of elasticity and ultimate tensile stress values of 14.8 GPa and 604 MPa, respectively. Corresponding latewood fibers had modulus of elasticity and ultimate tensile stress values that were, respectively, 33 and 73% higher. These differences are attributable to microfibril angles and pitting. Juvenility as defined by the mechanical properties of individual wood fibers is not a cylindrical cone surrounding the pith but appears to be biconical, tapering from the base to below the live crown and then again from the live crown to the apex

Mechanical Properties of Individual Southern Pine Fibers. Part III: Global Relationships Between Fiber Properties and Fiber Location Within an Individual Tree

This is the third and final paper in a three-part series investigating the effect of location within a tree on the mechanical properties of individual wood tracheids. This paper focuses on the definition of juvenile, transition, and mature zones as classified by fiber stiffness, strength, microfibril angle, and cross-sectional area. The average modulus of elasticity and ultimate tensile stress of all loblolly pine fibers were, in equal proportion of earlywood and latewood, 17.3 Gpa and 824 Mpa, respectively. The average microfibril angle was found to be 15.4 degrees, with rings 5 and 48 averaging 26.8 and 6.1 degrees, respectively. Normalization of all mechanical and physical properties showed that the juvenile zone is not cylindrical but rather biconical, tapering from stump to below the live crown and then again from the live crown to the bole tip. The transition zone parallels the juvenile zone, ranging in width from 3 to 15 rings. Fiber properties continued to improve slightly throughout the duration of the mature zone

Using DNA Metabarcoding to Identify the Floral Composition of Honey:A New Tool for Investigating Honey Bee Foraging Preferences

Identifying the floral composition of honey provides a method for investigating the plants that honey bees visit. We compared melissopalynology, where pollen grains retrieved from honey are identified morphologically, with a DNA metabarcoding approach using the rbcL DNA barcode marker and 454-pyrosequencing. We compared nine honeys supplied by beekeepers in the UK. DNA metabarcoding and melissopalynology were able to detect the most abundant floral components of honey. There was 92% correspondence for the plant taxa that had an abundance of over 20%. However, the level of similarity when all taxa were compared was lower, ranging from 22–45%, and there was little correspondence between the relative abundance of taxa found using the two techniques. DNA metabarcoding provided much greater repeatability, with a 64% taxa match compared to 28% with melissopalynology. DNA metabarcoding has the advantage over melissopalynology in that it does not require a high level of taxonomic expertise, a greater sample size can be screened and it provides greater resolution for some plant families. However, it does not provide a quantitative approach and pollen present in low levels are less likely to be detected. We investigated the plants that were frequently used by honey bees by examining the results obtained from both techniques. Plants with a broad taxonomic range were detected, covering 46 families and 25 orders, but a relatively small number of plants were consistently seen across multiple honey samples. Frequently found herbaceous species were Rubus fruticosus, Filipendula ulmaria, Taraxacum officinale, Trifolium spp., Brassica spp. and the non-native, invasive, Impatiens glandulifera. Tree pollen was frequently seen belonging to Castanea sativa, Crataegus monogyna and species of Malus, Salix and Quercus. We conclude that although honey bees are considered to be supergeneralists in their foraging choices, there are certain key species or plant groups that are particularly important in the honey bees environment. The reasons for this require further investigation in order to better understand honey bee nutritional requirements. DNA metabarcoding can be easily and widely used to investigate floral visitation in honey bees and can be adapted for use with other insects. It provides a starting point for investigating how we can better provide for the insects that we rely upon for pollination

Mechanical Properties of Individual Southern Pine Fibers. Part I. Determination and Variability of Stress-Strain Curves with Respect to Tree Height and Juvenility

This paper is the first in a three-part series investigating the mechanical properties of loblolly pine fibers. This paper outlines the experimental method and subsequent variation of latewood fiber mechanical properties in relation to tree position. Subsequent papers will deal with differences between earlywood and latewood fibers and effect of juvenility and tree height on global fiber properties. In this paper, the mechanical properties were determined on individual wood fiber with a user-built tensile testing apparatus. Cross-sectional areas of post-tested fibers were determined with a confocal scanning laser microscope and used to convert acquired load-elongation curves into stress-strain curves. The modulus of elasticity and ultimate tensile stress of loblolly pine latewood fibers tested in this study ranged from 6.55 to 27.5 GPa and 410 to 1,422 MPa, respectively. Fibers from the juvenile core of the main stem were on the low end of the mechanical property scale, whereas fibers beyond the twentieth growth ring were near the high end of the scale. Coefficient of variation for fiber stiffness and strength averaged around 20 to 25%. The shape of the fiber stress-strain curves is dependent on their growth ring origins: Mature fibers were linear from initial loading until failure, whereas juvenile fibers demonstrated curvilinearity until about 60% of maximum load followed by linear behavior to failure

The similarity of plant taxa found in nine honey samples using DNA metabarcoding and melissopalynology.

<p>The number of taxa detected (at family, genus or species level) is divided into those found with both techniques and those found using only one method. The taxa found using melissopalynology only are further subdivided into those where multiple pollen grains were found and those characterised with just a single grain. The values in the pie chart are the % of taxa within each category.</p

Species and genera found in more than one honey sample for DNA metabarcoding and melissopalynology.

<p>Species and genera found in more than one honey sample for DNA metabarcoding and melissopalynology.</p

The locations of the honey samples analysed using DNA metabarcoding and melissopalynology.

<p>Honey samples were provided by domestic beekeepers from hives located in gardens or smallholdings. The vegetation surrounding the hives was characterised based on descriptions from the beekeepers and observation of aerial images. H1 and H1_2 were two samples taken from the same hive.</p><p>The locations of the honey samples analysed using DNA metabarcoding and melissopalynology.</p