Abstract
High-resolution X-ray computer tomography (microCT) is a well-established technique to analyse three-dimensional microstructures in 3D non-destructive imaging. The non-destructive three-dimensional analysis of lichens is interesting for many reasons. The examination of hidden structural characteristics can, e.g., provide information on internal structural features (form and distribution of fungal-supporting tissue/hypha), gas-filled spaces within the thallus (important for gas exchange and, thus, physiological processes), or yield information on the symbiont composition within the lichen, e.g., the localisation and amount of additional cyanobacteria in cephalodia. Here, we present the possibilities and current limitations for applying conventional laboratory-based high-resolution X-ray computer tomography to analyse lichens. MicroCT allows the virtual 3D reconstruction of a sample from 2D X-ray projections and is helpful for the non-destructive analysis of structural characters or the symbiont composition of lichens. By means of a quantitative 3D image analysis, the volume of internal cephalodia is determined for Lobaria pulmonaria and the external cephalodia of Peltigera leucophlebia. Nevertheless, the need for higher-resolution tomography for more detailed studies is emphasised. Particular challenges are the large sizes of datasets to be analysed and the high variability of the lichen microstructures.
Highlights
Published: 13 July 2021The availability of non-destructive 3D examination technologies and increases in personal computer hardware and software enables various 3D graphical applications, such as surface visualisations of biological specimens
We examined the shape and number of external and internal cephalodia in Peltigera leucophlebia and Lobaria pulmonaria, respectively
The L. pulmonaria sample had a total volume of 2.091 mm3 (Table 2) and nine cephalodia of volumes ranging from 0.000046 to 0.004525 mm3
Summary
The availability of non-destructive 3D examination technologies and increases in personal computer hardware and software enables various 3D graphical applications, such as surface visualisations of biological specimens. MicroCT may be a beneficial tool, providing a complementation to other morphological examinations It allows the visualisation and analysis of internal lichen microstructures, which could not be observed using routine light microscopy alone or can only be seen partially (with the need of preparing cross-sections). The two lichens Lobaria and Peltigera have a green alga as the primary photobiont and incorporate nitrogen-fixing cyanobacteria into gall-like structures, the cephalodia. These are located either on the thallus surface (external cephalodia) or in its interior (internal cephalodia) [19]. The shape and size of the internal cephalodia of L. pulmonaria were examined
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