Fungal and algal community structures and their relationships with soluble salts at the Dazu Rock Carvings, China.

Fungi and phototrophic microorganisms can lead to the deterioration of heritage materials. In this study, Dazu Rock Carvings, a representative stone cultural heritage in China, was selected as the study site. Biofilms with different visible colors were systematically sampled and compared, as color serves as an easily observable in situ indicator reflecting differences in microbial composition and micro-environmental conditions. High-throughput sequencing was employed to characterize microbial community structure and composition, and their relationships with environmental factors were analyzed. The results showed that fungal and phototrophic communities differed among biofilms of distinct colors. Yellow biofilms were dominated by Hypocreales and Oculatellales, white biofilms by Agaricales and Vischeria, while green biofilms harbored diverse fungi (Pleosporales, Sporidesmiales, Verrucariales, Hypocreales) and elevated phototrophs (Nostocales, Didymodon), reflecting color-associated microbial composition patterns. Green biofilms exhibited the highest fungal alpha diversity, whereas white biofilms showed the highest phototrophic microbial alpha diversity, probably reflecting niche differentiation and distinct responses of fungi and phototrophic microorganisms to local micro-environmental constraints. Canonical correspondence analysis indicated that pH and multiple soluble ions were associated with variations in microbial community structure, suggesting that microbial assembly was shaped by the combined effects of local chemical conditions rather than by a single salt factor. The growth of cyanobacteria and fungal hyphae may penetrate or expand pore structures in the stone substrate, thereby exacerbating physical deterioration. These findings clarify the differences in community structure of biofilms with different colors, which is helpful to deepen the current understanding of sandstone biological degradation.