A NEW SLEDGE MICROTOME TO COMBINE WOOD ANATOMY AND TREE-RING ECOLOGY - BRILL
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452 IAWAIAWA
Journal 36 (4),
Journal 362015: 452– 459
(4), 2015
A new sledge microtome to combine wood anatomy
and tree-ring ecology
H. Gärtner 1,*, S. Lucchinetti 2, and F.H. Schweingruber1
1 Swiss Federal Research Institute WSL, Landscape Dynamics/ Dendroecology, Zürcherstrasse 111,
8903 Birmensdorf, Switzerland
2 Schenkung Dapples, Mechanische Werkstatt, Flühgasse 80, 8008 Zürich, Switzerland
*Corresponding author; e-mail: holger.gaertner@wsl.ch
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
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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).
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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.
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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 (± 1 µm)
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.
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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. An 800-µm-
thick section (small image, section fixed between two glass slides) was cut from the core using
a stable microtome blade.
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Figure 5. – A: Reproduction of “Nördlinger” sections of exposed roots (thickness 60 µm);
A1 and A4: Fagus sylvatica; A2 and A3: Larix decidua. – B: Examples for the range of pos-
sible sample sizes to be sectioned with the Lab-Microtome (cross sections; scanned slides and
related micro photos); B1: Acer campestre, stem, sample size 1.2 × 8.5 cm; B2: Fagus sylvatica,
exposed root, sample size 3.3 × 2.4 cm; B3: Pinus sylvestris, stem, sample size 1.1 × 6.5 cm;
B4: Piper nigrum, stem, sample size 0.5 × 0.5 cm; B5: Cycas circinalis, leaf, enrolled, sample
size 0.1 × 0.3 cm.
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sectioned should be water-saturated. The problem is the fact that the entire sample gets
softened when it is completely water-saturated and, as a result, bigger samples tend to
be deformed (= pressed upward) in the centre while cutting because of the relatively
high forces always occurring while the knife cuts off a section. In extreme cases, the
sample is lifted up in the central part to such an amount, that the knife gets stuck in the
sample.
A solution for this problem is to fix the sample dry in the holder. Then just moisten
the surface of the sample with water by using a brush, wait for a moment until it is
soaked in the upper part of the sample and start cutting. Make sure, that the part to be
sectioned is always wet when cutting. The way a sample needs to be fixed in the holder
always depends on the specimen. The construction allows disks of branches, roots or
small stems up to a diameter of 2.5 cm to be fixed directly in the clamps of the holder.
The same is true for rectangular samples (inner size of sample holder: 2.5 × 6 cm).
Special clamps were developed to allow cutting 5-mm and 10-mm increment cores
up to a length of 6 cm, but also micro cores taken using, e. g., a Trephor device (Rossi
et al. 2006) having a 2-mm diameter (Fig. 3B). Moreover, the ability to fix 10-mm
cores enables preparing cores for isotopic analysis. The surface can be prepared to
analyze the common ring structure and micro sections can be taken to further analyze
the anatomical structure without contaminating the remaining sample. Furthermore,
when stabilizing the blade with the pole, 800 µm sections can be cut from the core
(Fig. 4) for “en bloc” cellulose extraction before the annual rings are separated from
the section for isotopic analyses (e. g., Schollän et al. 2014). This procedure also re-
quires to fix the core dry in the holder. Only the surface needs to be wetted for trimming
the core to a certain amount and then soak the surface until roughly a 1-mm layer is
soaked before the micro sections can be cut.
The stability of the construction even enables cutting the so-called “Nördlinger”
sections (Fig. 5), if the samples are fixed dry in the holder.
Conclusion
A big drawback in sectioning woods until nowadays was the fact that samples were
restricted to a relatively small size. The enhanced stability of the Lab-microtome helps
resolving this problem and enables cutting a wide range of specimens, from petioles
to long radii sampled from tree trunks (Fig. 5).
References
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Accepted: 10 August 2015
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