Microscopic findings and soil genetic “indicators” in support of pedoarchaeological studies

Abstract

Archaeologists use historical artefacts and archaeological records to reconstruct the communities that produced them and the environment in which they lived. Soil protects our buried or damaged heritage of archaeological and historic remains from depletion, damage, and any disturbance. Here are presented some preliminary results obtained in the framework of the FP7 Project "MEditerranean MOntainous LAndscapes: an historical approach to cultural Heritage based on traditional agrosystems (MEMOLA)" where ancient soils horizons are themselves archaeological records. In order to implement the MEMOLA archaeological study and to identify soil genetic "indicators", two integrated approaches were used: 2) Ancient DNA extraction from soils and sediments and 2) a screening of microscopic details of soil sediments of archaeological horizons by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In fact, DNA contained in soils and sediments can provide novel insights into past environments and ecosystems. This represents the first step to explore the biodiversity and to potentially study the biodiversity of recent and no longer existing environments, in order to reconstruct the past landscapes (as proposed by project MEMOLA). In particular, looking for genetic markers of the former presence of vascular plants, and peculiar soil microorganisms that can hypothetically reveal important historical and paleo-ecological aspects that could help researchers depicting an ancient scenario, or telling facts happened in the past. Microorganisms are an integral part of soils, their assemblages and communities can be strong indicators of specific biomes, climatic conditions or vegetation coverage, and can have an important documentary role in archaeological studies. Soil microorganism can long withstand stressful conditions by transforming to a resting state, for example, and thus act, as testimonial of past environments and peculiar ecosystems no longer present. The scanning electron microscope (SEM) is a tool that allows the microscopic anatomy of the surfaces of organic or inorganic samples to be examined under high magnification; when coupled with a microanalysis probe (energy dispersive spectroscopy or EDS) one can also learn about the elemental chemical composition of the materials examined by SEM. SEM-EDS analysis has allowed us to document the structure of carbon and mineral particles found in the sediments. Ancient carbon remains can maintain many micro morphological details of the plants and vegetal parts buried in the deep soil horizons, moreover other micro-traces like phytolithes (siliceous bodies from plants), diatoms or carbonaceous micro-fossils could represent useful "indicators" in support of pedoarchaeological studies.