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A New Sledge Microtome to Combine Wood Anatomy and Tree-Ring Ecology

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A New Sledge Microtome to Combine Wood Anatomy and Tree-Ring Ecology 452 IAWAIAWA Journal Journal 36 (4), 36 2015: (4), 2015 452–459 A NEW SLEDGE MICROTOME TO COMBINE WOOD aNaTOMY aND TREE-RING ECOLOGY H. Gärtner1,*, S. Lucchinetti2, and F.H. Schweingruber1 1Swiss Federal Research Institute WSL, Landscape Dynamics/Dendroecology, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland 2Schenkung Dapples, Mechanische Werkstatt, Flühgasse 80, 8008 Zürich, Switzerland *Corresponding author; e-mail: [email protected] AbsTracT Based on the Reichert Om E microtome a more sophisticated, nevertheless solely mechanically operated microtome was developed enabling to section specimens of various forms and sizes. The materials used and the special construction of the microtome resulted in a higher stability of the moving parts whilst simultaneously reducing weight. As a result of the high stability of the sledge guidance, bigger sections can be cut enabling more detailed analyses of anatomical structures within plant stems, roots or branches as well as their variation back in time. Consequently, wood anatomical parameters can be integrated more easily in time-series analyses supporting the aims of a quantitative wood ecology. Keywords: Dendroecology, sectioning, time-series analyses. [In the online version of this paper Figures 1–5 are reproduced in colour.] InTrodUcTion For detailed wood anatomical studies within the scope of a changing climate, the prep- aration of sections is essential to strengthen the understanding of the form and func- tional evolution of the xylem in different climatic regions. Nevertheless, details about micro-technique, especially the application of microtomes have hardly been discussed in scientific publications (Bracegirdle 1978; Gärtner & Nievergelt 2010; Gärtner & Schweingruber 2013; Gärtner et al. 2014, 2015). Most wood anatomical analyses are done on small specimens, mostly blocks of about 1 cubic cm to cut transverse, radial and tangential sections. To analyse age-dependent or environmentally induced anatomical variations, e.g., along a cross section of a tree stem, the ability to section bigger specimens would be of importance, but most current microtomes are not capable to cut big sections. The inability of cutting bigger sections of more or less dense woody material is as- tonishing when thinking about the serial production of big sections (2 × 5 cm; thickness 50–100 µm) prepared by Herrmann Nördlinger at the end of the 19th century (Nördlinger 1852–1888). The technical base for preparing sections of that size does no longer exist (Bubner 2008). However, when focussing on an anatomically based, annually resolved reconstruction of environmental conditions of the past, large sections are required to © International Association of Wood Anatomists, 2015 DOI 10.1163/22941932-20150114 Published by Koninklijke Brill NV, Leiden Downloaded from Brill.com10/06/2021 03:15:28AM via free access Gärtner et al. – Sledge microtome for tree-ring ecology 453 reduce the amount of sample preparation needed to an affordable minimum. Big sec- tions will allow to expand wood anatomical research to a highly resolved, time related, ecologically based wood anatomy. With this, the ability of analyzing new parameters and developing new methodologies to understand the short- and long-term effects of environmental factors on woody plant bodies is given. A first step in this direction was the development of the core microtome (Gärtner & Nievergelt 2010) for cutting micro sections of entire increment cores (Gärtner et al. 2015; Ivanova et al. 2015) as well as the GSL1 microtome (Gärtner et al. 2014). As a further step towards combining wood anatomy and dendroecology, we present a new sledge microtome enabling to cut big specimens of all forms for the detailed analyses of structural variations within the respective plant part to be analyzed back in time. Reichert OmE sled (block) sliding surfaces microtome body (cast iron) WSL-Lab-Microtome microtome body (aluminum) Figure 1. Photograph of a common Reichert Om E microtome (upper image) used as a base for the development of the WSL-Lab-Microtome (lower image). Downloaded from Brill.com10/06/2021 03:15:28AM via free access 454 IAWA Journal 36 (4), 2015 The Lab-microtome Basic principles A basic requirement for cutting sections of wood, no matter if using rotation or sledge microtomes, is the stability of the device. This is the main reason why old (and also recent) microtomes are extremely heavy, mostly made of (cast) iron. The pure weight of the device guarantees stability during the sectioning procedure. One of the most practicable sledge microtomes for wood anatomical purposes (although no longer produced) is the Reichert sledge microtome Om E (Fig. 1). Its design proved to be applicable for small specimens ranging from low to high density. The bigger the threaded rod to fix the stopper for the platform knife-holder block opening for stabilizing pole knife-holder platform sled 1 sled 2 angled stop for automated sample uplift linear guide 1 linear guide 2 stopper for the platform a b c Figure 2. Construction of the knife-holder platform. – a: Stabilizing pole in position; b and c: knife holder stabilized by the pole for cutting sections of high density woods. Downloaded from Brill.com10/06/2021 03:15:28AM via free access Gärtner et al. – Sledge microtome for tree-ring ecology 455 sample and/or the higher the density, the higher the forces occurring while cutting. When a certain threshold is exceeded, the knife is lifted up and cutting sections is no longer possible. We cannot specify this threshold, because it varies depending on the respective combination of sample size and density. For instance, we realized that it is not possible to cut a continuous thin section (15 µm) of a larch stem sample (Larix decidua Mill.; sample size: 1 × 3 cm) without special treatment (e.g., boiling), if severe compression wood occurs within the sample. Construction We aimed at developing a more sophisticated, nevertheless manually operated mi- crotome while increasing stability and nevertheless reducing weight. Consequently, the body of the microtome was constructed as a frame consisting of four aluminum plates forming the base for all components of the microtome. The knife holder is placed in the centre of an aluminum platform, which is mounted on two small sleds running on linear guides (Fig. 2). The central axis of the two guides are fixed parallel (spacing: 7 cm) on the top facing the aluminum plate of the micro- tome frame. The ball-bearing guided sleds only allow a two-dimensional movement (forward/backward). The ball bearings do have hardly any internal play (± 1µm) providing maximum stability of the knife holder in all directions other than along the guides while cutting. The knife holder (Fig. 3) used for the Lab-microtome was initially designed for the core microtome (Gärtner & Nievergelt 2010). Basically it is constructed the same way as the old proven holders in the past, but made of aluminum. The knife (or removable Figure 3. A: Side view of the mounted knife holder of the Lab-Microtome; 1: Knife-holder block; 2: Bar to adjust the vertical angle (arrows) of the knife; 3: Spherical head fixing the horizontal position of the knife-holder block on the platform. The position can be changed by opening and closing the head (see small arrows); 4: Two screws are used to fix the position of the knife (or 5: removable blade holder) in the block; 6: Knife-holder platform (compare Fig. 2). – B: Core holders of three different sizes (10, 5 and 2 mm diameter, length 6 cm) were developed to be placed in the sample holder of the microtome. Downloaded from Brill.com10/06/2021 03:15:28AM via free access 456 IAWA Journal 36 (4), 2015 blade holder) is horizontally and vertically adjustable to adapt its position depending on the size and density of the sample. When sectioning samples of high density, the knife holder can be additionally fixed with a small pole. This pole is placed 3.5 cm left of the threaded rod fixing the knife-holder block on the platform (Fig. 2). At this position, the pole stabilizes the knife holder and prevents it from being turned sideward around the threaded rod (compare Fig. 2a–c). The sample holder is placed within a frame that allows a fine correction of the ori- entation of the sample when it is basically fixed in the clamps to allow a precise cutting of transverse, tangential or radial sections. The frame is set on a pole which is placed into a mount fixed on an aluminum plate which is guided by two sleds running along parallel linear guides. The precise upward movement of the platform and with this of the sample is realized by a micrometer screw connecting the platform and a hand wheel allowing for upward movements of the sample in steps of 1 µm. The semi-automatic uplift system is constructed in the same way as it was done for the Reichert OM E. Sectioning procedure The basic sectioning procedure is comparable for all samples. After adjusting the optimal orientation of the sample in the holder (e.g., perpendicular to the longitudinal axis for transverse sections), the sample is fixed tight to prevent it from moving during sectioning. Depending on the size and density of the material, the vertical angle of the blade needs to be adjusted (Fig. 3A). The more dense the material is, the steeper the angle of the knife needs to be. The exact position has to be adapted for each specimen, in general an angle of about 20° (indicated on the side of the blade holder; Fig. 3A) is applicable for most softwoods. Although it is common practice to place the entire sample in water for several minutes before sectioning to soften the material, at least for bigger samples only the part to be Figure 4. Photograph of a 10-mm core fixed in the core holder of the microtome.
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