Biodeterioration Control of the Longhu Pagoda Stone Heritage, China: Identification of Deteriogens and Evaluation of Biocidal Efficacy

Longhu Pagoda, a national key cultural heritage site located at the southern foot of Hushan Mountain in Liubao, Jinan, Shandong Province, is a masterpiece of Tang-dynasty stone pagoda architecture and a core component of the Shentong Temple heritage complex alongside the Four Gates Pagoda. The pagoda features a distinctive “Tang-dynasty body, Song-dynasty crown” structure: its stone base and main body, carved with intricate high-reliefs of dragons, tigers, heavenly kings, arhats, and apsaras, date back to the late Tang Dynasty (717–845 AD), while the brick eaves and roof were reconstructed during the Northern Song Dynasty. Severely threatened by biodeterioration induced by bryophytes, lichens, and associated microorganisms, the pagoda’s exquisitely carved stone surface has undergone irreversible aesthetic degradation and structural weakening, threatening its thousand-year-old artistic integrity. Biocide treatment is a commonly adopted strategy for stone heritage conservation. This study aims to characterize the specific biodeteriogens colonizing Longhu Pagoda and evaluate the efficacy of various biocides for targeted conservation intervention. In this study, biological samples collected from Longhu Pagoda were first identified: bryophyte samples contained chloroplasts, with some having morphological characteristics similar to Pottiaceae or Grimmiaceae; symbiotic algae isolated from lichen samples were identified as Chlorella sp.; four dominant fungal strains were isolated via morphological observation and molecular sequencing (ITS), namely Aspergillus niger (F1), Trichoderma yunnanense (F2), Talaromyces ruber (F3), and Aspergillus aflatoxiformans (F4). On this basis, the inhibitory effects of different biocides on dominant deteriorating organisms were systematically evaluated via chlorophyll fluorescence analysis, algal growth inhibition tests, and oxford cup assays, combined with field verification on Longhu Pagoda. The optimal biocide with stable inhibition efficacy and favorable stone compatibility was screened out. The results provide technical support for the biological conservation of Longhu Pagoda and similar stone cultural relics suffering from microbial biodeterioration.