Study On Marine Primary Production By Fast Repetition Rate Fluorometry

Phytoplankton primary productivity process is one of the most important processes in marine ecosystems.It is the beginning of the food chain and drives the function of marine biological pump.It is of great significance to carbon fixation and storage of marine ecosystems as well as global change.At present,the methods of measuring marine primary production is mainly 14C,3C isotope tracer,dissolved oxygen and so on.However,a newly chlorophyll induced fluorescence technique-Fast Repetition Rate fluorometry(FRRf)is emerging in the latest twenty years.It can not only measure the electron transport rate of photosystem ?(ETRPS?)rapidly,and also some important photosynthetic parameters.In this study,we investigated Kuroshio influenced region of the South China Sea and Yangtze River plume influenced region of the East China Sea.We established a new method to calculate ETRPPS?.In the meanwhile,combined with the data of phytoplankton net primary production(NPP)by 14C,photosynthetic pigments et al.?the influence of Kuroshio intrusion and Yangtze River plume on photosynthetic activity and primary production were studied,.The main results are as follows:(1)Compared with 14C isotope tracing method,ETRPPS? and NPP had a good correlation(p<0.0001),the profile distribution characteristics of ETRPPS? and NPP were very similar in the euphotic zone,and it was found that ETRPS? and NPP were not coupled with chlorophyll a concentration.At the same time,different ETRPS?/NPP ratios(?e:C,Electron requirement for carbon fixation)were observed in different sea areas and seasons.The values of ?e:c in the ESC in summer,Taiwan Strait in summer,SCS and Luzon Strait in winter,South China Sea and Luzon Strait in summer were 2.44,5.26,9.08 and 10.70 respectively.The regulation of ?e:c is:the ECS in summer<the Taiwan Strait in the summer<the SCS and the Luzon Strait in the winter<the SCS and the Luzon Strait in the summer.And ?e:c is mainly regulated by nutrients and phytoplankton groups.Lower the concentration of nutrients,smaller the size of phytoplankton,higher ?e:C,and lower quantum carbon fixation efficiency.(2)In the South China Sea basin,the Daliy-ETRPS? and NPP of SEATS station affected by Kuroshio were approximately three times higher than SS1 station,which was not influenced by Kuroshio.At the same time,the functional cross section of PSII(aps1i)and functional PSII reaction center concentration(RCII)of SEATS station which was affected by Kuroshio were higher than those of SS1 station which was not affected by Kuroshio,but the influence on PSII maximum quantum efficiency(Fv/Fm)to Kuroshio intrusion could be neglected.In the Luzon Strait,the photosynthetic activity and primary productivity of phytoplankton could be improved by mix:ing the Kuroshio water with the South China Sea in an appropriate proportion.When the mixing proportion of Kuroshio reaches 50-70%(F4 station),the photosynthetic activity of phytoplankton,electron transfer rate and primary productivity of photosynthetic system? reach the maximum.Ave.Fv/Fm-100(Every depth averaged Fv/Fm in the upper 100 m),Ave.?PS?-100(Every depth averaged ?PS? in the upper 100 m)and Ave.RC?100(Every depth averaged RCII in the upper 100 m)at F4 station were 0.437,2.01 nm2 and 0.638 nmol/m3 respectively.And the Ave.Fv/Fm-ioo,Ave.aps?100,Ave.RC?100 at L5 station were 0.404,1.76 nm2 and 0.326 nmol/m3 respectively.At the same time,the integrated ETRPS? in the euphotic zone(IETRPS?)of F4 was approximately 2.5 times higher than that of L5,while the integrated NPP(INPP)in the euphotic zone of F4 was approximately 7.5 times higher than that of L5.(3)In terms of phytoplankton community composition,compared with less influenced region by Yangtze River plume,the composition of phytoplankton community in the area more influenced by Yangtze River plume tended to transfer from Pico(Synechococcus)to Nano(Prasinophytes,Cryptophytes).It could be observed that the concentration of Fv/Fm and RCII in the area more effected by Yangtze River plume were obviously higher than those less affected by Yangtze River plume(p<0.05),while opsii of the former was not significantly higher than opsii of the latter(p>0.05).In addition,the Daily-ETRPPS? of surface phytoplankton was significantly increased,which was caused by the Yangtze River diluted water(p<0.05),but the integrated Daily-ETRPS? of euphotic zone was not significantly increased(p>0.05).However,the integrated Daily-ETRPS? of euphotic zone reached higher level at intermediate influenced region by Yangtze River plume(intermediate surface salinity and light attenuation coefficient).It was because of the high turbidity of more influenced area by Yangtze River plume,and less concentration of chlorophyll a and nutrients of less influenced area by Yangtze River plume that integrated Daily-ETRPS? was at lower level in this two regions.However,when the light quantum numbers,nutrients and chlorophyll a were relatively sufficient in the meanwhile,the integrated Daily-ETRPS?of euphotic zone reached higher level.