Influence of soil bacteria and carbonic anhydrase on karstification intensity and regulatory factors in a typical karst area

Sequestration of atmospheric CO2 is attracting considerable attention due to global warming. Karstification significantly affects the sequestration of atmospheric CO2. Microorganisms and carbonic anhydrase (CA) can promote karstification, but the actual contribution of microorganisms and CA to karstification intensity (KaI) under natural conditions remains unclear. In this study, the influence of soil microorganisms and CA on KaI and main regulatory factors was investigated through field soil column dissolution experiments. Guilin Yaji Karst Experimental Site was used as the typical karst area, and Silai clastic rock area was the control area. Results showed that surface soil in various geomorphological positions in the karst area presented KaI in the following order: saddle > slope > depression. Addition of composite CA-producing microbial inoculants or composite inhibitors regulated CA activity in surface soil, thereby influencing KaI. Illumina high-throughput sequencing results indicated that the soil dominant bacterial phyla were generally the same in various experimental groups and plots, and the bacterial abundance in surface soil was regulated by additives. Addition of composite microbial inoculants increased the total bacterial abundance of surface soil, whereas addition of composite inhibitors reduced the total bacterial abundance. The ratio of CA-producing bacterial abundance to total bacterial abundance was the largest at saddle in the karst area, in corresponding to the highest KaI. This finding suggested the significant role of CA-producing bacteria in promoting KaI. Correlation analysis revealed that the main soil regulatory factors of KaI were soil pH, total hydrogen, total organic carbon, and exchangeable calcium.