Effects Of Long-term Ocean Acidification On The Formation And Germination Of Resting Spores Of Ditylum Brightwellii

With the rapid development of human society,the amount of CO2 emitted by industrial production and fuel combustion is increasing every year,which has become an irreversible trend in recent years.Excessive CO2 emissions are absorbed into the atmosphere and absorbed by the vast oceans,causing ocean acidification.Ocean acidification has had a tremendous impact on marine ecosystems,the Earth's environment,and climate,and has therefore become a research hotspot in recent years.Excessive absorption of CO2 by the ocean leads to an increase in dissolved CO2,while the pH of the seawater decreases,affecting the growth and reproduction of marine organisms,the primary productivity of phytoplankton,and the community structure of marine ecosystems.As an important part of the marine ecosystem,diatoms are also affected by ocean acidification.Many diatoms form resting spores when the environment becomes harsh,which is also considered a survival strategy for diatoms.The formation and germination of resting spores affects the survival of diatom populations,and also affects the community structure of marine diatoms and the outbreak of diatom blooms.The various physiological effects of ocean acidification on phytoplankton have been reported by many scholars.The effects of various conditions on diatom resting spores have also been studied.However,the synergistic effect of ocean acidification and nitrogen limitation on the production and germination of diatom resting spores is still rarely studied.In this study,the ocean acidification conditions were simulated in the laboratory by introducing CO2 into the medium.The experiment set high CO2 concentration group(CO2 concentration 1000 ppmv,High CO2,hereinafter referred to as HC group)and low CO2 concentration group(CO2 concentration 400 ppmv,Low CO2,hereinafter referred to as LC group),the Ditylum brightwellii as the research object was long-term cultured in this environment,and the nitrogen-induced resting spore and the resting spore germination experiment were carried out regularly.Cell density,resting spore formation rate,pH,photo synthetic efficiency,chlorophyll,nutrient concentration and other parameters were used to analyze the effects of long-term ocean acidification on the formation and germination of resting spores of D brightwellii.The main conclusions of this study are as follows:(1)In the f/2 medium,ocean acidification has a weak promotion effect on the growth rate of the exponential growth period of D.brightwellii,and significantly increases the peak density of the cell population of D.brightwellii.The peak density of the HC group was about 3 × 104—9×104/mL,and the peak density of the LC group was about 1.5×104—4 × 104/mL,which was significantly lower than that of the HC group.In the nitrogen-deficient ESAW medium,ocean acidification had no significant efTfect on the growth rate of D.brightwellii.(2)During the formation of resting spores of D.brightwellii,the pH of the medium was stable,and the acidification group and the control group were 7.41(±0.02)and 7.97(±0.04),respectively.Nitrate was rapidly consumed in the early stage of the experiment,and dropped to about 1 ?mol/L on the third day,and then remained in the lower range.Phosphate and silicate concentrations also decrease to some extent,but generally maintain a high concentration range.The Fv/Fm was higher in the first 3 days,about 0.60,and then gradually decreased,and the lowest value was about 0.40.The Chl a content continued to rise for the first 3 days and then began to slowly decrease.(3)Ocean acidification inhibits the formation of resting spores in the nitrogen-deficient state of the two-tailed algae.In the first generation of induced dormant spores,the formation rate of resting spores in the HC group and the LC group was 57.46%and 59.69%,respectively,and the formation rate of the LC group was slightly higher than that of the HC group.In the subsequent resting spore induction experiment,the LC group was higher than the HC group.The average formation rate of the resting spores in the HC group was 54.62%,and the average in the LC group was 63.13%.The mean value of the LC group was significantly higher than that of the HC group.Therefore,it can be considered that ocean acidification has a certain inhibitory effect on the production of resting spores by the nitrogen limitation of D.brightwellii.(4)Resting spores induced under short-term ocean acidification conditions have higher germination speed and germination rate.In the HC group and the LC group,no resting spore germination was observed on the first day of the germination experiment.In the first 3 days,the germination rates of HC group and LC group were 63.46%and 49.48%,respectively.The germination rates of HC group and LC group were 71.54%and 61.94%respectively in the first 5 days,and no resting spore germination occurred after 5 days.Most of the resting spores in both groups were germinated in the first 3 days.The germination speed of the HC group was higher than that of the LC group,and the germination rate was also higher than that of the LC group.The average germination rate of HC group was 73.65%in the multiple germination experiments of D.brightwellii cultured under long-term acidification conditions,and the average germination rate of LC group was 68.63%.The average germination rate of the HC group was slightly higher than that of the LC group.Statistical analysis showed that there was no significant difference between the two groups.The germination rate of the HC group or the LC group varied greatly with the algebra,but there was no obvious change trend.