Characteristics Of Inorganic Carbon Utilization By Chlorella And Nostoc Calcicola Breb Based On Isotope Tracer Technique

This thesis reveals that the stable carbon isotopic fraction fractionation of two kinds of karst microalgae?Chlorella and Nostoc Calcicola Breb?using inorganic carbon and distinguish the fractionating value amonging by CA?carbonic anhydrase?in two kinds of karst microalgae transfering HCO₃^-into Intracellular.And then using ¹³C-NaHCO₃ to establish a hybrid model for two kinds of microalgae inorganic carbon utilization.Finally,using the stable carbon isotope fractionation in CO₂ assimilation process,we calculated the share of microalgae utilizing inorganic carbon under different CO₂ concentrations.The results show that both karst microalgae can use HCO₃^-as carbon source when CO₂cannot meet their growth needs.On the one hand,two kinds of karst microalgae use inorganic carbon as the carbon element for growth.On the other hand,karst microalgae use calcium ions in water to produce calcium carbonate precipitation.In the process of carbon utilization,light ¹²C transferred to the algae and CaCO₃ making ¹³C enrichment in DIC and CO₂,and ¹²C enrichment in algae and CaCO_3.Compared with the light culture and dark culture experiments,it is found that illumination results in-1.3‰fractionation when Nostoc Calcicola Breb absorbing DIC?Dissolved inorganic carbon?.This process is influenced by the??coefficient of photosynthesis fractionation?.Light causes Chlorella take up about-1.1‰DIC fractionation in the utilization of inorganic carbon,and pH affects the value of?¹³C_DIC.Compared with field culture and laboratory culture,Nostoc Calcicola Breb and Chlorella DIC fractionation decreased by 6.8‰and 6.25‰per thousand,respectively.P?pressure?is an important factor of?13C_DIC,and T?temperature?determines?13Calgae.In addition to the effect of light on the carbon stable isotope fractionation,the temperature and pressure in the natural environment are important factors affecting the stable carbon isotope fractionatio n of microalgae in karst water.By adding extracellular CA inhibition study,it is found that the stable carbon isotope fractionation effect caused by extracellular CA should be paid attention to in the study of paleoclimate with microalgae stable carbon isotopes.The fractionation effect caused by CA from different algae is different.It should be distinguished when model is calculated.Cell type and cell volume affect the stable carbon isotope fractionation of CO₂ during the assimilation of karst microalgae.In the process of CO₂ assimilation,the stable carbon isotope fractionation of the Chlorella is 16.53‰,and the Nostoc Calcicola Breb is 15.63‰.Microalgae in karst water showed long-term adaptation to environment.the Microalgae which exist in Karst underground river outlet principal using HCO₃^-as carbon source.The utilization share of two microalgae to HCO₃^-can be over 96%.karst microalgae could adapt the habitat impact of elevated carbon dioxide by rapidly regulating its carbonic anhydrase activity in the environment of less than 3%carbon dioxide concentration.The activities of carbonic anhydrase in Chlorella increased by 1.46 times and Nosioc calcicola Breb increased by 2.12 times respectively in the environment of 2.5%carbon dioxide concentration.In response to the challenge of global war ming,Karst microalgae play an important role in coping with the decrease of pH and HCO₃^-.With the increase of incubation time,the pH and the HCO₃^-in the culture environment is recovered,indicating that the karst area is an important participant to Regulating water pH.in the karst area,microalgae?13C_DIC values affected by karst geological conditions.Under CO₂ conditions,DO is an important factor that can not be ignored.Although CA enzyme can not directly affect?¹³C_DICIC value,it can indirectly affect the value of?¹³C_DIC.The concentration of CO₂ will lead to increased use of share of two microalgae on using HCO₃^-.