Analysis by next-generation sequencing of bacterial communities in Japanese cedar logs buried for 2 years for ground improvement

Abstract Optimizing the effectiveness of the log-piling method, developed in Japan to mitigate soil liquefaction during seismic activity, relies on understanding log deterioration and bacterial interactions. This study explored the role of bacterial communities in degradation of logs buried in the ground for 2 years, focusing on the relationships between bacterial composition, soil environmental factors, and wood deterioration. Next-generation sequencing was employed to analyze the bacterial communities within the logs and the surrounding soil. Soil environmental factors such as pH, total carbon, total nitrogen, and the C:N ratio were measured to evaluate their influence on bacterial community structure. Bacterial communities in the logs predominantly originated from the surrounding soil, with shifts in taxon abundance driven by environmental conditions. Depth below the soil surface had a more substantial influence on bacterial community structure than soil environmental factors. Members of the classes Alphaproteobacteria and Gammaproteobacteria , particularly the orders Rhizobiales , Burkholderiales , and Enterobacterales , were primarily responsible for the observed minor log cell wall degradation, although the wood density did not change significantly during the experimental period. Our findings suggest that bacterial activity plays a role in early wood deterioration, and further research could help to improve the use of logs in ground improvement to enhance their durability in preventing soil liquefaction.