Artificial lighting as a manageable anthropogenic driver of microbial risks in subterranean stone heritage

Artificial lighting in grottoes creates persistent light pollution that can act as a controllable anthropogenic disturbance, reshaping surface microbial communities and increasing biodeterioration risk to stone heritage. To evaluate the ecological effects of light pollution, biological covers on sandstone surfaces in the Longyou Grottoes were investigated under artificial light, sunlight, and dark conditions using 16S rRNA high-throughput sequencing and metagenomic sequencing. Microbial communities were dominated by Bacteria, with relative abundances exceeding 98% in most samples. Cyanobacteriota were markedly enriched under artificial light and sunlight, both exceeding 40% relative abundance, whereas Pseudomonadota and Actinomycetota dominated in darkness. Community structure differed significantly among the three light environments, and the dark environment showed the highest alpha diversity and the most complex co-occurrence network. Neutral community model and normalized stochasticity ratio analyses indicated that community assembly under artificial light was more strongly driven by stochastic processes, whereas sunlight- and dark-associated communities were mainly governed by environmental filtering. Functional analysis showed that the biofilm protection ratio increased with light intensity. Artificial light favored assimilatory nitrogen and sulfur metabolism, darkness promoted nitrification, denitrification, and sulfur oxidation, and sunlight enhanced nitrogen fixation potential. These results demonstrate that artificial light pollution not only alters microbial community structure and assembly, but also changes metabolic strategies and potential microbe–material interactions on heritage surfaces. Artificial lighting should therefore be treated as a key management factor, together with humidity and salt migration, in strategies for biodeterioration control and sustainable conservation of grotto heritage.