Microbial succession and microclimatic fluctuation in purple chromatic anomaly on Terracotta Warriors Pit 1

A purple chromatic anomaly emerged on the earthen surfaces of UNESCO Terracotta Warriors Pit No. 1. Integrating microscopy, 16S/18S rRNA sequencing, and microclimatic monitoring, we identified specialized troglophilic cyanobacteria ( Iphinoe sp. LOS-B1 and the Oscillatoriales EcFYyy-200 clade) as the dominant colonizers (>60% of surficial mats, up to 70% at epicenters). These taxa, previously known only from calcareous subterranean habitats, displayed violet-granulated cytoplasm, cylindrical-torulose cells (5–7 × 6–10 μm), and sheath-mediated hormocyst release—first documented on earthen heritage. Microclimatic data revealed a transient winter window (January–March 2023) with elevated illuminance (600–7,200 lux), frequent low humidity (relative humidity [RH] < 45% on 42.3% of days), and stable cool temperatures (−4°C to 10°C). This regime created a photic niche, enabling the rapid expansion of pre-adapted cave cyanobacteria. These findings demonstrate that semi-enclosed heritage sites can experience localized microbial outbreaks under specific microclimatic regimes, highlighting the need for integrated environmental and microbiological monitoring in conservation.