Decay patterns and associated microbial communities in waterlogged archaeological compression wood from an organic-rich wetland deposit

By integrating microscopy with microbial community analyses, we investigated microbial degradation of waterlogged archaeological compression wood (CW) from an organic-rich wetland deposit (hard pine, AD 682–719). Erosion bacterial decay predominated in both earlywood (EW) and latewood (LW) CW tracheids, with tunneling bacterial decay more frequent in EW and soft rot more frequent in LW. The highly lignified outer S 2 layer (S 2L ) was degraded either by gradual erosion from exposed surfaces toward the middle lamella or by simultaneous attack from the inner S 2 and outer S 1 layers. In the latter pathway, preferential S 1 degradation preceded complete S 2L degradation through erosion or tunneling bacterial activity. Degradation was more extensive in ray parenchyma cells and ray tracheids than in adjacent CW tracheids. Microbial community analyses identified ascomycetous fungi as potential contributors to soft rot, while dominant bacterial taxa were mainly associated with metabolic and environmental processes that may indirectly facilitate wood degradation rather than direct degradation of wood cell wall components. Overall, these findings provide a broader environmental context for previously reported variability in microbial decay behavior of CW, highlighting that both burial environment and the degree of CW development (mild to severe) may influence microbial decay patterns in waterlogged archaeological CW.