Influence of CO2/HCO3- on Microbial Communities in Two Karst Caves with High CO2

There is limited knowledge about microbial communities and their ecological functions in karst caves with high CO2 concentrations. Here, we studied the microbial community compositions and functions in Shuiming Cave ("SMC", CO2 concentration 3 303 ppm) and Xueyu Cave ("XYC", CO2 concentration 8 753 ppm) using Illumina MiSeq high-throughput sequencing in combination with BIOLOG test. The results showed that Proteobacteria, Actinobacteria and Bacteroidetes were dominant phyla in these two caves, and Thaumarchaeota was the most abundant in the rock wall samples of SMC. The microbial diversity in the water samples decreased with increasing HCO3- concentration, and it was higher in XYC than that in SMC. The microbial community structures in the sediment and rock wall samples were quite different between the two caves. High concentrations of CO2 can reduce the microbial diversity on the rock walls in karst caves, probably through changing microbial preference for different types of carbon sources and decreasing the microbial utilization rate of carbon sources. These results expanded our understanding of microbial community and its response to environments in karst caves with high CO2.