Temporal niche partitioning of bacterial communities shaped by hydrologic fluctuations and drought regimes in karst caves

Abstract Background In monsoon regions, wet-dry cycles may establish environmental gradients that influence both the richness and composition of cave bacterial communities. However, how bacterial communities in different cave niches respond to wet-dry cycles remains poorly understood. Results Here, we examined the responses of three major cave habitats (bedrock, speleothem, and sediment) to wet-dry cycles spanning two drought events. Overall, sediment bacterial richness and diversity increased during dry seasons but decreased in rainy seasons, whereas bedrock/speleothem communities exhibited the opposite pattern—showing an increase during wet periods and maintaining stability. In this process, ventilation and drip water explained the majority of compositional variance in bedrock and speleothem bacterial communities. By mapping indicator species onto co-occurrence networks, we found that species co-occurrence explained compositional differences in sediment bacterial communities between the two drought events. However, this relationship was not observed in bacterial communities associated with bedrock or speleothem. Additionally, ecological drift showed a negative correlation exclusively with sediment bacterial richness. Conclusions Taken together, transport processes mediated by ventilation and drip water facilitate the post-drought recovery and stability maintenance of bacterial communities colonizing bedrock and speleothem surfaces. However, neutral processes exerted stronger influences on sediment bacterial communities, enhancing their vulnerability to drought.