| 其他摘要 | The increasing concentration of CO2 has been an unneglected global issue. The carbon sink effects by karstification attract more and more extensive attention, whereas microalgae play an important role in biokarst process. Not only microalgae can promote the carbonate dissolution, forming the “ Carbon Sink ”, but also can utilize the DIC from the carbonate dissolution, forming the biological sequestration and leading to the precipitation of CaCO3. Therefore, a coupling system of “water (H2O)-rock(CaMg(CO3)2)-gas(H2O)-biology(CH2O)” interaction will be formed with the participation of mircroalgae in the karst dynamic system, which has a great influence on the global carbon cycle. The Extracellular Carbonic Anhydrase (CAext) and the anion channel are the significant pathways for the CCM mechanism of mircoalgae being realized and play a major part in the coupling system. In addition, the PCO2 and pH also have great controlling effect on the interaction between microalgae and carbonate. The typical microalgae (i.e.C.R, C.P and M.A) in karst lakes were collected in this reasearch. With the laboratory-controlled simulations method, we performed our experiment on different concentration of Acetazolamide (AZ), anion channel inhibitors (DIDS) and gradients of pH in the nutrient solution added with calcite powder under open or isolated CO2 conditions. Using the two-way isotope tracer model, the biological dissolution quantitative model and reverse recognition technology, we successfully quantified the effect on the biological dissolution of calcite, resulting from CAext, the anion channel, PCO2 and pH of water. On this basis, we evaluated the direct and indirect carbon sequestration ability of microalgae in karst lakes every month in the whole year, as well as the effect of microalgae CAext on its carbon sequestration. The present study leads to the following conclusions: 1. With the increasing concentration of AZ, the amounts of Mg2+ released from calcite per unit algal biomass and unit time in C.R decrease, accordingly, the utilized proportion of the carbon in calcite by microalgae increase. Thus, the CAext of microalgae can promote the biological dissolution of calcite, contrarily, the CAext of microalgae can also catalyze and utilize the HCO3- in water, resulting the precipitation of CaCO3. In general, the CAext of microalgae has a negative effect on carbon sink effects by biological dissolution of calcite. 2. With the increasing DIDS, the amounts of Mg2+ released from calcite per unit algal biomass and unit time in M.A decrease, accordingly, the utilized proportion of the carbon in calcite by M.A decrease. The anion channel, on the one hand, can promote the biological dissolution of calcite by ultilizing the HCO3- in water, on the other hand, will lead to the precipitation of CaCO3 with the ultilization of HCO3-. In summary, the union channel play a more exceeded effect on the CaCO3 precipitation than the dissolution effect of calcite, therefore, it has a negative effect on carbon sink effects by biological dissolution of calcite as well. 3. The PCO2 outside, on the one hand, affect the activity of CAext, on the other hand, control the chemical dissolution of calcite. With the decreasing PCO2, the total dissolution amounts decrease, and the biological dissolution of microalgae decrease. However, this will promote the utilized proportion of carbon in calcite and enhance the biological sequestration ability of DIC from calcite by microalgae. 4. For the C.R, with strong CAex activity, the amount of Mg2+ released from calcite per unit algal biomass and unit time in microalgae decrease with the increasing pH, contrarily, the C.P and M.A, with less or no CAext activity behavior reversely. In addition, the utilized proportion of carbon in calcite decrease with the increasing pH in water. Overall, the lesser pH, the more amount of inorganic carbon from calcite is utilized by microalgae and form DIC, thus, the net carbon sink effects become |
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