## 4 Discussion  
### Effects of the F/B on In Situ CO\({}_{2}\) Fluxes  
In present study, the abundance of bacteria and fungi in KA was higher than that in NKA, which indicated that higher soil nutrients shaped higher abundance of microorganisms. In KA, high levels of cations (such as Ca\({}^{2+}\) and Mg\({}^{2+}\)) tend to combine with easily decomposed organics to form more stable large aggregates and organic carbon \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Microbial Taxa** & **Groups** & **Region** & **Percentage** & **Correlation Coefficient** \\ \hline Bacteria & Acidobacteria Gp6 & KA & 7.05\% & \(-\)0.565 \({}^{*}\) \\ Fungi & _Stellatospora_ & NKA & 0.07\% & 0.571 \({}^{*}\) \\ Functional & Plant pathogen & KA & 2.61\% & 0.582 \({}^{*}\) \\ groups of fungi & Endomycorrhizal-plant & & & \\ pathogen-undefined & & & & \\ saprotroph & & & & \\  & Dung saprotroph- & & & \\  & endophyte-litter & & & \\  & saprotroph & & & \\  & saprotroph & & & \\ Functional & Aerobic nitrite oxidizers & & & \\   groups of bacteria & (Nitrifiers) & & & \\ \hline \hline \end{tabular} Note. \({}^{*}\) Significant at the 0.05 level (two-tailed); KA, karst areas; NKA, non-karst areas.  
\end{table} 
Table 2: Correlation between soil respiration and bacterial and fungal functional. Figure 6: The heatmap clustering and distribution of bacterial (**a**) and fungal (**b**) functional groups. Note: KA, karst areas; NKA, non-karst areas. pools [40; 41]. Therefore, compared with fungi, bacteria are more susceptible to partly inhibition in KA environment. The higher contents of chitin and chitosan in fungi cell wall could not be easily degraded, so that the total biomass of fungi was significantly higher than that of bacteria, which indicated that refractory organic matter form fungi is an important sources of SOC accumulation [42]. Long-term combination of organic and inorganic fertilization increased SOC accumulation of paddy fields in South China. The numbers of fungi and bacteria both also increased significantly, but fungi increased more than bacteria, thereby increasing the F/B [14]. [PERSON] argued that fungi didn't have greater growth efficiency than bacteria in greater C storage and slower C turnover in fungal-dominated soils [43]. [PERSON] et al. [40] reported that there was a significant correlation between the SOC and F/B with the reason of increased fungal necromass resulting in a change in the SOC composition. The above result is in accordance with the findings of higher SOC content and F/B in KA in present study. The KA with high temperature and humidity, the dissolution of carbonate brings a large amount of Ca\({}^{2+}\) and HCO\({}_{3}\)\({}^{-}\) into the soil. HCO\({}_{3}\)\({}^{-}\) combines with H\({}^{+}\) in the water to generate CO\({}_{2}\), which increases soil CO\({}_{2}\) concentration [44]. Though some CO\({}_{2}\) in KA soil was consumed through reversibly combining with H\({}_{2}\)O to form H\({}_{2}\)CO\({}_{3}\) to a certain [3], CO\({}_{2}\) concentration of surface soil in KA is still higher than that in NKA. The higher concentration of soil CO\({}_{2}\) also change the quantity and quality of soluble sugars, organic acids, amino acids and other compounds secreted by rice roots. The bacterial abundance was significantly decreased and the fungal abundance and biomass were significantly increased, resulting in a significant increase in the F/B as previously reported [45; 46]. More studies in the past 20 years have shown that the primary producers of CO\({}_{2}\) in soils are microorganism [13; 14; 47]. In present study, soil respiration in KA was lower than that in NKA, and the communities of both bacteria and fungi in KA were also significantly different with those in the NKA. Moreover, the F/B was higher in the KA than in the NKA. We also found that there was a significant negative correlation between soil respiration and the F/B across KA and NKA. In KA, soil carbon turnover rate would increase due to the changes on soil physical properties and the effect of fungi on physiology [43].