Scanning Electron Microscopy Protocol for Studying Anatomy of Highly Degraded Waterlogged Archaeological Wood

Angela Balzano,Maks Merela,Katarina Čufar

doi:10.3390/f13020161

Abstract

Waterlogged archaeological wood (WAW), approximately 4500 years old, from the prehistoric pile-dwelling settlement at Ljubljansko barje, Slovenia, was examined by scanning electron microscopy (SEM). We propose a simplified protocol for sample preparation and the SEM technique for the study of highly degraded WAW of Quercus, Faxinus, Acer, Salix and Populus, representing taxa with different wood properties. We present the advantages of the proposed technique for wood identification, the observation of various anatomical features and for the study of cell wall degradation. SEM, equipped with energy-dispersive X-ray spectroscopy (EDX), allowed us to detect significant amounts of Fe, S and Ca with different appearances, amounts and distributions in the wood of the studied taxa. In the case of Populus, an increased amount of Si was also detected. The applied SEM protocol allowed characterisation of the anatomy of the highly degraded WAW while reducing the time required for sample preparation and examination under the microscope, as well as extending the lifetime of the SEM components (e.g., tungsten filament), compared to the situation when we analyse wood samples with a greater volume.

Highlights

Archaeological wood is an important source of information about the past
We developed a scanning electron microscopy protocol (SEM) that allows simple but effective preparation of Waterlogged archaeological wood (WAW) for observation of large surfaces at low magnification, which is important for the study of wood anatomy and identification, while allowing observation of the progression of cell wall degradation at higher magnification and resolution
Unlike conventional protocols that sputter gold, we coated the samples with carbon only

Summary

Introduction

Archaeological wood is an important source of information about the past. It is the main material source in dendroarchaeology, a sub-discipline of dendrochronology, whose original focus on providing absolute dating is extended by the application of modern techniques that allow the reconstruction of past practices of wood selection and use, as well as the evolution of past environments and human societies [1,2].Archaeological wood is mostly preserved in waterlogged environments where it becomes saturated with water and, anoxic or suboxic conditions are created [3].Waterlogged archaeological wood (WAW), in environments with a low availability of oxygen, is over time invaded by fungi and bacteria that can degrade the cell walls. Archaeological wood is an important source of information about the past. Archaeological wood is mostly preserved in waterlogged environments where it becomes saturated with water and, anoxic or suboxic conditions are created [3]. Waterlogged archaeological wood (WAW), in environments with a low availability of oxygen, is over time invaded by fungi and bacteria that can degrade the cell walls. There are erosion bacteria that can be active under conditions of extremely low oxygen [4,5,6,7,8]. Erosion bacteria often coexist with other wood-degrading microorganisms, such as tunnelling bacteria and soft rot fungi [9]

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