Unveiling the dual role of biocolonization: a case study on the deterioration and preservation of sandstone monuments in Leshan Giant Buddha, China.

For large, open-air lithic cultural heritage, colonization is an inevitable process. This study examines the dual impact of colonization on the Leshan Giant Buddha's sandstone monuments, focusing on both biodeterioration and protection. Over three years, we conducted field surveys and monitored biocrusts (bryophytes, lichens, and biofilms) on these monuments, observing significant biodeterioration primarily due to mechanical exfoliation and acid corrosion. To assess the potential of biota in conserving sandstone monuments, we replicated biotic crust colonization on laboratory sandstone samples. In the laboratory, we observed biomineral formation, primarily calcium carbonate, on the rock specimen surfaces after two years. Comparative analysis with control samples showed that biocolonization notably changed the rock's hydrophobicity, surface hardness, and weight loss, indicating a protective effect. Further analyses using XRD, SEM-EDS, and transcriptomics identified carbonic anhydrase as a key enzyme in the biomineralization process. Our findings suggest that under controlled conditions, biocolonization can be steered towards bioprotection, offering new strategies for the in-situ preservation of open-air lithic cultural heritage.