Long-Term Efficacy of Essential Oil Treatments on Monument Biofilms and Microbial Recolonization

Open-air stone monuments, such as the Feilaifeng Cliff Carvings (Hangzhou, China), are highly vulnerable to persistent microbial colonization and biodeterioration. Essential oils (EOs) have recently been proposed as environmentally compatible antimicrobials, yet their long-term performance and the ecological trajectories of post-treatment recolonization remain insufficiently understood. Here, we systematically evaluate three EO-based delivery strategies – EO combined with water-repellent agents (TEB), EO loaded in polyacrylonitrile membrane (TPA), and EO encapsulated in chitosan nanoparticles (TCC) – through an integrated assessment combining field monitoring, microscopy, chromatic analysis, high-throughput sequencing, diversity metrics, differential abundance testing, and co-occurrence network modeling. Among the three approaches, the TEB formulation displayed the most sustained inhibitory effect on microbial colonization under open-air conditions. Microbial community analyses revealed that Chlorophyta functioned as pioneer recolonizers following treatment, with deterministic processes predominantly governing biofilm reassembly. The observed attenuation patterns of EO efficacy and the associated shifts in bacterial and fungal community structures provide mechanistic insights into recolonization dynamics on treated stone surfaces. These findings offer an evidence-based foundation for designing adaptive, long-term biocontrol strategies for the preventive conservation of open-air stone heritage.