Microbial biofilms on a giant monolithic statue of Buddha: The symbiosis of microorganisms and mosses and implications for bioweathering

Monolithic statues of Buddha are important cultural heritage objects. The inevitable coverage by moss with associated microorganisms is believed to drive weathering, but the functions of moss in bioweathering are still unclear. In this study, mosses and their associated microorganisms of the Leshan Giant Buddha in China from three distinct periods (e.g., growing, senescent, and residual) were examined using High-throughput sequencing and quantitative PCR techniques. The results showed that the period of active moss growth rather than species had a regulatory role on the microenvironment, which further affected the microbial communities and metabolism. The higher frequency of nucleotide sequences related to enzymes of nutrient cycling and weathering in the growing period indicated active interaction between microorganisms and substrate. Moss growth increased energy allocation to substratum surface through photosynthesis. Higher abundance of the ammonia monooxygenase gene (amoA) of the ammonia-oxidizing archaea was detected and responsible for nitrogen transformation. In particular, moss growth promoted iron-associated processes and likely electron transport processes. Iron-reducing bacteria were the main players responsible for transforming iron oxides on the statue. It is concluded that moss growth plays an important role in driving microbial weathering. This study highlights the urgency of moss symbiosis control for protecting monolithic statues in the field.