Enzyme activities and compositional shifts in the community structure of bacterial groups in English wetland soils associated with preservation of organic remains in archaeological sites

To extend our previous research on preservation in situ of organic archaeological remains in wetland soils, physicochemical variables and extracellular enzyme activities (β-d-glucosidase, phosphatase, and leucine aminopeptidase) were measured in two archaeological wetland soils in northern England, from the soil surface down to 100 cm during two years. These two locations, with a proven potential to contain and preserve archaeo-environmental remains, were of interest because they had different hydrological and land-management history. In addition, for one of the sampling years, the structure of soil bacterial communities was monitored using polymerase chain reaction followed by denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rRNA gene-coding fragments amplified from soil DNA, using primers specific for eu bacteria, actinomycetes, and α-proteobacteria. The physicochemical monitoring data indicated that at Sutton Common the buried conditions were less stable and more heterogeneous throughout the soil profile than at Hatfield Moor. Extracellular enzyme activities decreased with depth at both sites and higher average enzyme activity was found at Hatfield Moor than at Sutton Common. Phosphatase and leucine aminopeptidase were the most active enzymes throughout the soil profile. Our results indicated that the enzymatic potential for organic matter (OM) degradation at both sites was strongly correlated to pH and OM content in the soil. DGGE patterns for eubacterial, α-proteobacteria, and actinomycete populations indicated intra-site changes in community structure with time of sampling and depth. The sampling site with a high and stable water table, Hatfield Moor, showed higher enzyme activities above 50 cm depth and as a consequence had more potential for OM degradation than the site with fluctuating hydrological conditions. These trends provide insight into the potential for biodegradation over time and with depth at these two sites, information that is relevant to the in situ preservation of buried organic archaeological artefacts in wetland soils.