The Interactive Effects Of CO₂ And Temperature On The Physiology Of Marine Phytoplankton

In this thesis,the coccolithophore Emiliania huxleyi NIWA1108 and Emiliania huxleyi PMLB was selected to assess the effects of ocean acidification and warming on their physiological responses.A laboratory semi-continuous incubation experiment was conducted.Six experimental treatments were performed:10?,partial pressure of carbon dioxide(pCO2)400 ppm;15?,pCO2 400 ppm;25?,pCO2 400 ppm;10?,pCO2 800 ppm;15?,pCO2 800 ppm;25?,pCO2 800 ppm.The results showed that the optimum growth temperature for the two strains of coccolithophores was 15?.Increasing or decreasing the temperature reduced the size of the coccosphere,and the contents of chlorophyll a(Chl-a),particle organic nitrogen(PON),particle organic phosphorus(POP).Elevating pCO2 increased the cellular Chl-a,PON and POC contents of NIWA1108,but decreased its cellular POP content.The cellular Chl-a,PON and POP contents of PMLB also increased with the rising pCO2,whereas,it had no significant effect on POC content of PMLB.The PIC/POC ratio of NIWA1108 was reduced under high temperature or high pCO2 condition,and the ratio decreased further with the combined effect of high temperature and pCO2,and decreased with the sinking rate.It showed that the high temperature and acidification have a potential synergistic effect on the physiology and biogeochemical indicators of coccolithophores,especially calcification.Furthermore,we also conducted a shipboard continuous incubation experiment on the coastal and open sea of the South China Sea.Four experimental treatments were examined with 2 temperature sets:original seawater temperature,4? higher than it,and 2 pCO2:400 ppm,800 ppm.The experimental results showed that the effects of high temperature and acidification on the composition of phytoplankton community in different sea areas had similarities and differences.The POP and PIC concentrations and PIC:POC ratio decreased in both sea areas,when the temperature and pCO2 increased at the same time.On the condition of high temperature and pCO2,the ratio of POC:PON decreased,while the Chl-a concentration and PON:POP ratio increased in the inshore area.However,the oceanic area had the opposite trend.With the simultaneous action of high temperature and high pCO2,the community structure of phytoplankton in the nearshore and oceanic stations changed,and the sedimentation rate decreased significantly.Overall,this series studies help us understand the potential interactive effects of ocean acidification and warming on marine phytoplankton related biogeochemistry.