Study On The Physiological Responses Of The Coccolithophore Emiliania Huxleyi To Ocean Acidification And Aluminum

Since the industrial revolution,the extensive use of fossil fuels and the destruction of land vegetation and ecosystems have sharply increased the concentration of CO₂in the atmosphere,and also led to the ocean acidification.The physiological and biochemical effects of a series of Marine environmental factors caused by the increase of p CO₂level on phytoplankton have received much attention,especially the Marine calcification organisms.Different calcified phytoplankton have different responses to ocean acidification,and coccolithophores,as one of the most important calcified phytoplankton,have been widely concerned about their physiological and ecological effects.However,there is still a lack of scientific understanding and exploration on the possible changes of environmental factors（such as aluminum and variable light environment）and their compound effects under acidifying Marine environment,as well as the relevant responses of coccolithophores.In this paper,the physiological and evolutionary responses of Emiliania huxleyi to ocean acidification were investigated under the conditions of acidified seawater,varying aluminum concentration and light intensity.The main results are as follows:1.The physiological response of Emiliania huxleyi cultured in dark at low temperature（16℃）and normal temperature（20℃）under low CO₂（400μatm,pH8.2,LC）and high CO₂（1000μatm,pH7.8,HC）levels was explored.At the same temperature level,there was no significant difference in cell abundance between high and low CO₂condition,and the cell abundance at 20℃was 83.4%lower than that at16℃.At the same temperature,the initial particulate organic carbon（POC）content under high CO₂condition was 16.1%higher than that under low CO₂condition.With the extension of dark culture time,the POC content of all treatments decreased significantly.At the end of the dark period,the POC of the high CO₂condition at 20℃was the most significant decrease,which was 38.4%,while the low CO₂condition at16℃was the lowest decrease frequency.There was no significant difference in the POC reduction rate between the other two treatments,which was about 25%.The initial particulate organic nitrogen（PON）content per unit volume was not significantly different between high CO₂and low CO₂condition.At 16℃,the final PON content in HC condition decreased by 9.3%compared with the initial content,while the final PON content in low CO₂condition had no significant change.At 20℃,the final PON content of high CO₂and low CO₂treatments increased by 20.5%and 14.8%,respectively.The results showed that the increase of CO₂concentration significantly increased the carbon consumption of Emiliania huxleyi,induced to enhance its energy storage capacity,and made it absorb more inorganic carbon in the deposition process,which aggravated the acidification of CO₂concentration increasing with the increase of depth in the phobophobic zone.2.The physiological response of Emiliania huxleyi growing in seawater with no Al（0 nmol/L,NAl）,low Al（200 nmol/L,LAl）and high Al（2000 nmol/L,HAl）concentrations at low CO₂（400μatm,pH8.2）and high CO₂（1000μatm,pH7.8）levels was investigated.Under low CO₂conditions,the specific growth rate of NAl and LAl treatments had no significant difference,but was higher than that of HAl treatment under high CO₂conditions,the growth rate of NAl and LAl culture was inhibited,while that of HAl culture was not affected.Under low CO₂conditions,the addition of Al had no effect on the yield of POC（LAl）,but slightly increased the yield of POC（HAl）.With the increase of CO₂concentration,the POC yield of NAl treatment increased by 55.3%,but with the addition of 0.2μmol/L Al,POC yield increased by22.3%.The response regularity of PON yield,cell POC and PON content to different treatments was consistent with that of POC yield.Al had no effect on particulate inorganic carbon（PIC）production rate and PIC/POC ratio at low CO₂conditions,while the increase of CO₂concentration significantly decreased the PIC production rate and PIC/POC ratio in LAl and HAl medium.This results indicate that high CO₂might increase carbon export to ocean depths by enhancing the efficiency of the biological pump at low Al levels occurring in natural seawater（200 nmol/L）,and this could have large implications for the ocean carbon cycle.3.The physiological response of Emiliania huxleyi growing in seawater with no aluminum（0 nmol/L,NAl）,low aluminum（200 nmol/L,LAl）and high aluminum（2000 nmol/L,HAl）at three light levels:2500 lux（low light,LL）,4500 lux（adapted light,AL）and 10000 lux（high light,HL）.Under the condition of AL,high aluminum treatment decreased the cell growth rate,while low aluminum treatment had no significant difference;under LL condition,both LAL and HAl treatment could promote cell growth,while under HL condition,LAl treatment had no significant effect on the cell growth,but HAl treatment inhibited the cell growth.The content of chlorophyll an in the cells of Emiliania huxleyi was also regulated by light intensity and aluminum concentration.Under the condition of AL,LAl treatment did not affect the content of chlorophyll a,but HL treatment increased the content of chlorophyll a in the cells;when the algae was under LL condition,both LAl and HAl treatment could inhibit the synthesis of chlorophyll a per unit cell.Under the condition of HL,there was no significant change in LAl treatment compared with NAl,but HAl treatment significantly promoted the yield of chlorophyll a.Different from chlorophyll a content,in NAl treatment medium,the change of aluminum concentration had no significant effect on Fv/Fm value,but under LAl condition,HL treatment had an inhibitory effect on it;HL treatment further enhanced the decreasing effect of Fv/Fm value under HAl condition,and reduced this value to 42%of that under LL condition.The experimental results show that the addition of appropriate aluminum is beneficial for the algae to survive in the changeable surface water in the future,and alleviate the damage of cells in the process of sinking,while high concentration of aluminum will inhibit its growth and physiology.This is of great significance for us to understand the carbon cycle and ecological changes in the ocean in the future.