Changes Of Fatty Acids Composition In Nitzschia Closterium Under Nitrogen Limiting Conditions

In recent years,the frequency,area and scope of red tides in China have become larger and larger,and the losses caused by them have become more and more serious.At present,the red tide is only based on the principle of prevention and prevention,and there is no accurate and effective monitoring.Indicators to forecast red tides.In order to better understand the mechanism of red tide occurrence and the new method of monitoring red tide,this paper mainly uses laboratory culture method to measure the red tide in the process of red tide in the process of red tide.Important monitoring indicators(cell growth,pH,chlorophyll a concentration,five nutrient salt concentrations,?13C,?15N values and relative fatty acid content of microalgae cells).The ?13C,?15N values,the relative content of fatty acids,the composition of the biomass and microalgae cells under nitrogen-limited conditions were discussed.The main experimental results are as follows:Although the number of cells in N.closterium is slowly increasing under the condition of nitrogen deficiency,there is no obvious change of growth cycle,such as logarithmic phase or stable phase.There was a significant negative correlation between biomass and chlorophyll a concentration in the nitrogen-deficient group,and the pH value in the culture medium was increasing in both experiments.There was a significant positive correlation between c(NO2-N)and c(NH3-N)and microalgae biomass in the control group,c(Po43--P),?(NO3--N)and p(SiO32--Si)showed a significant negative correlation with microalgal biomass.In the nitrogen-deficient group,the ?13C value decreased first and then increased,and the?15N value did not change significantly,and the range of variation was small.In different growth cycles,the fatty acid content in the rhododendron was not the same.In the stable and decaying microalgae,MUFA is accumulated in large amounts.In the nitrogen-deficient group,MUFA accounted for a greater proportion of total fatty acid content;by comparing the fatty acid composition of the control group and the nitrogen-deficient group,the two fatty acids C18:3n-3 and C24:ln-9 were only present in the nitrogen-deficient group.In the group.The conclusion is as follows:In the red tide process,the ?13C value must be changed before the ?15N value,which is more sensitive.The ?13C value can be used as the red tide monitoring index;after the red tide occurs,two fatty acids will appear in the red tide algae(C18:3n-3 and C24:ln-9),therefore,these two characteristic fatty acids can also be used as indicators for monitoring red tides;during the occurrence of red tide,the fatty acid synthesis pathway changes,the fatty acid content and composition of nitrogen source to C16 and above Will have a very significant impact,leading to the accumulation of MUFA.Innovative results of this research:(l)Using the method of stable isotope analysis,the ?13C and ?15N values of the whole rhizosphere of Rhododendron were analyzed.(2)Eight kinds of fatty acids in N.closterium were analyzed,and two fatty acids under nitrogen restriction conditions were identified as fatty acid biomarkers after red tide.