Influence Of Soil Bacteria And Carbonic Anhydrase On Karstification Intensity And Regulatory Factors In Karst Area

The recycle of atmospheric CO2 attracts wide attention due to the global warming, and karstification has a significant effect on the recycle of atmospheric CO2. Although previous studies have demonstrated that microorganisms and carbonic anhydrase(CA) can promote karstification, but the actual contribution of microorganisms and CA to the intensity of karstification still need to be investigate. In this paper, Yaji Karst Experimental Site in Guilin was chosen as the typical karst area, and Silai clastic rock area as the control. The effects of microorganisms and CA to the intensity of karstification and the regulation factors were investigated through soil column leaching experiments in the fields. Moreover, the bacterial diversity and abundance of surface soil in different experimental groups and different physiognomy positions were studied using High throughput sequencing and real-time PCR. The relationship between the diversity and abundance of soil bacteria and the strength of karstification was discussed. The main results obtained in this paper are as follows:(1) The intensity of karstification in the surface soil at different geomorphological positions in the Karst Experimental Site showed Saddle>Slope>Depression. The addition of composite microbial agents which could produce CA and composite inhibitors which could regulate the CA activity of topsoil affected the intensity of karstification. Affected by temperature and rainfall, the topsoil karstification intensity was higher in summer and autumn than that in spring and winter. The main soil regulatory factors of karstification intensity was pH, total hydrogen, organic carbon and exchangeable calcium of soil.(2) The predominant topsoil bacteria at different geomorphological positions in karst area was basically the same as the superior bacteria which mainly includes Acidobacteria?Proteobacteria and Verrucomicrobia and their relative abundance varies with geomorphological positions. The differences in relative abundance of Acidobacteria and nitrospirae were related to soil pH and nitrogen content. The species and relative abundance of predominant soil bacteria of each experimental group was basically the same.(3) The addition of composite CA producing microbial agents decreased the bacterial diversity of topsoil, but increased the total bacterial abundance, the addition of composite inhibitors decreased the total bacterial abundance of topsoil, and its influence to the bacterial diversity was more complicated. The analysis on the abundance of topsoil dominant CA producing bacterias at each sampling site showed that, the ratio of CA producing bacterial abundance and total bacterial abundance in Saddle is the largest, corresponding to the highest intensity of karstification, whcih suggest that bacteria which produce CA has a significant promoting effect on the intensity of karstification.The results of this study provided a scientific basis for revealing the contribution of soili microorganisms and CA to the karst carbon sink under natural conditions, and strengthen the scientific understanding of the carbon sink potential in karst ecosystem.