Depth drives microbial assembly while localized tourism selectively enriches bacterial indicator taxa in Lake Fuxian,...

Microbial communities play crucial roles in maintaining lake ecosystem stability. In this study, high throughput 16S rRNA gene sequencing combined with diversity and multivariate statistical analyses was used to investigate how anthropogenic activities, particularly tourism, influence the vertical distribution and composition of bacterial and archaeal communities in Lake Fuxian, a deep oligotrophic freshwater lake in southwestern China.

A total of 26 bacterial and 3 archaeal phyla were identified, among which Proteobacteria (20.12-32.80%) and Cyanobacteria (17.08-30.39%) dominated the bacterial communities, while Thaumarchaeota (73.29-99.90%) dominated the archaeal ones. Bacterial α-diversity was overall higher than that of archaea but showed no significant variations across depths or sites, whereas archaeal diversity varied significantly with depth but not between sites.

Clustering, NMDS and redundancy analysis (RDA) revealed that depth established the primary ecological scaffolding for both bacterial and archaeal communities. However, tourism drove a localized, taxon-specific restructuring of bacterial communities in the upper layers, while archaeal communities were highly resistant to horizontal spatial disturbances overall. LEfSe analysis showed that Prochlorotrichaceae and Prochlorothrix_PCC-9006 were significantly enriched at the tourism-impacted site L, whereas Acidobacteria and Sphingomonas were dominant at the deep-water site D. Correlation and RDA analysis indicated that Cyanobium_PCC-6307 was positively correlated with TN (p ≤ 0.01), while the ammonia-oxidizing archaea Candidatus Nitrosopumilus and Candidatus Nitrosoarchaeum displayed opposite relationships with depth and nutrient parameters.

These findings highlight that tourism-related disturbance may alter upper-layer bacterial community composition in deep oligotrophic lakes and provide a critical theoretical basis for evaluating the micro-ecological risks of anthropogenic disturbances, guiding the sustainable tourism development and environmental management of deep plateau lakes.