Degradation of reburied archaeological wood piles after preservative treatment for twenty years

This study investigated the degradation mechanism and microbial communities of a reburied stone-fixed wooden pile (SP) after being excavated and treated with pentachlorophenol/polyethylene glycol (PCP/PEG) preservatives for a 20-year period at the Jin Zhongdu Watergate Heritage Cultural Site. High-throughput sequencing (HTS) techniques were combined with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrum analysis, and quantitative chemical analyses. A foundation wooden pile (FP) forming the watergate supports, which has been in service for nearly 870 years at the site, was also examined. The results showed that preservatives still partially remained in the SP after burial. More abundant and richer microbial communities were found in the SP (including brown rot, soft rot, white rot fungi and bacteria) due to the hydrophilic PEG providing more favorable habitats for microbial. Therefore, it was indicated that the PCP had gradually lost its antibacterial function. Although brown rot fungi had not been detected using HTS, typical morphological characteristics were observed in the FP using SEM, thereby the characteristics of brown rot fungi were the results of previous decay. The absence of brown rot may have been attributed the competition among wood rot fungi.