Interactive Response Of Phytoplankton Community To Ocean Acidification,Warming And Phosphate Enrichment

Increased carbon dioxide concentration in the atmosphere caused by human activities,leading to global warming and ocean acidification.By the end of this century,pCO₂ in the atmosphere is expected to increase from 390 ppm to 700 ppm or higher,resulting in a downward trend in the global average surface seawater pH.Changes in the global marine environment may change the biochemistry of phytoplankton and thus the community structure of phytoplankton.In this paper,through the East India Ocean Scientific Investigation Project of the National Foundation of China in 2018 and March-May 2019,the ship's one-time cultivation experiment and the ship-based continuous cultivation experiment were used to study the phytoplankton community in the East Indian Ocean.In-depth study on the physiological and ecological changes of phytoplankton under the environment of warming and phosphorus enrichment.Our experimental results are multifaceted.The results show that the steady increase in the concentration of Chl a during the entire experiment can explain the steady increase in the number of phytoplankton cells throughout the experiment,that is,as the marine environment changes,phytoplankton community cells can gradually adapt to the environment.The rate of carbon fixation of marine phytoplankton further decreases in ocean acidification and high temperature environments,which may be due to the destruction of photosynthetic protein functional genes in the ocean acidification environment,resulting in a decrease in the carbon fixation rate of phytoplankton communities.The carbon fixation rate of the phytoplankton community in the separate high-temperature environment is also very low,which may be attributed to the quota of cell carbon fixation rate,which is also related to cell size and strain-specific reactions.In the ocean acidification and warming environment,the nitrogen fixation rate of the nitrogen-fixing phytoplankton dominated by Chaetoceros also shows a downward trend,which is especially obvious in the combined environment of ocean acidification and warming.This may be because the decrease in seawater pH caused by ocean acidification will cause the organic nitrogen produced by nitrogen fixation to be transported to the vegetative cells around the heterotypic cells,thereby reducing the rate of nitrogen fixation in phytoplankton cells.The low pH marine environment reduces the efficiency of nitrogenase in phytoplankton cells,thereby reducing the ratio of each enzyme in the cell and further affecting the nitrogen fixation of phytoplankton community cells.Ocean acidification and warming environments have been shown to fix nitrogen Negative effect of enzyme efficiency.Our experimental results show that the cultivation results of different experimental treatment groups have no significant effect on the marine silicon(Si)cycle.This is because silicon in the ocean mainly exists in the form of a silicate(H4SiO4)buffer system.In the process of environmental changes,the protonation form of its buffer system will not be affected too much,so ocean acidification,warming and phosphorus-enriched environment have little effect on the change of biosilicon in phytoplankton cells.From the perspective of the response of phytoplankton communities to changes in the marine environment,our experiments confirmed that the increase of marine carbon dioxide concentration,temperature and nutrient phosphorus will affect the growth rate of phytoplankton community,of which temperature has a more significant effect on the growth of phytoplankton community.In the ocean acidification and warming(heating)experiments,diatoms and cyanobacteria have absolute advantages in the phytoplankton community,but under the high temperature and acidification environment of the ocean,the relative abundance of diatoms is very low,indicating that this environment does not Conducive to the growth of diatoms.Although dinoflagellates do not occupy a population advantage in this experiment,the experimental results show that compared to ocean acidification,ocean warming is the main factor that stimulates the growth of dinoflagellates,and ocean acidification is the main factor that inhibits the growth of dinoflagellates.The experimental results in the ocean acidification and eutrophication(phosphorus enrichment)experiments show that ocean acidification and high phosphorus seawater can promote the short-term trend of diatoms,but it is difficult to stimulate the growth of dinoflagellates.The stimulation of the growth of phytoplankton community may be due to the downregulation of the mechanism of carbon concentration mechanisms(CCMs)in the phytoplankton community after environmental changes,which may cause phytoplankton to absorb HCO3 directly or indirectly.Therefore,CO₂ absorption may be an important factor affecting the growth rate of phytoplankton.The absorption of nutrients can further promote the growth of phytoplankton communities,and meanwhile,competition among phytoplankton communities is also an important factor that affects the changes in the structure of phytoplankton communities in the marine environment.Thus,changes in the marine environment will have a profound impact on the phytoplankton ecology and community structure changes.