Studies On Photosynthetic Characteristics Of Phytoplankton In China Sea And The West Pacific

In this paper, photosynthetic characteristics of phytoplankton in China sea and the West Pacific were studied by using chlorophyll fluorescence technique, besides the in situ measurement, the effects of different phosphorus(P) concentrations and nitrogen(N)/P ratios on the growth and photosynthetic characteristics of Skeletonema costatum and Prorocentrum donghaiense were studied via laboratory controlled experiments. The main research work and conclusions are summarized as follows:(1). Photosynthetic characteristics of phytoplankton in winter in the Jiaozhou bay were measured by using Phyto-PAM. From the results we can know that though phytoplankton abundance was extremely low in December, strong photochemical activity combined with relatively stable hydrological, biological environment, and rich nutrients would lead to the peak of phytoplankton abundance in February in the Jiaozhou bay.(2). The detailed distribution of photosynthetic characteristics of phytoplankton in summer in the Yellow Sea and East China Sea was measured, the results show that photosynthetic characteristics and activity of phytoplankton were influenced by its biological characteristics and surrounding ecological factors, such as irradiance, nutrients and phytoplankton community. Meanwhile, the thermally strati?ed structure and the movement of water masses, such as the Yangtze River diluted water, the Yellow Sea cold water mass and other different water system, also had an important impact on phytoplankton photosynthetic activity and characteristics. F_v/F_m of phytoplankton in summer was significantly positively associated with nitrate content(NO2-), which reflects relationship between metabolism and photosynthesis of phytoplankton: accompanied by NO2- metabolism, photosynthesis and photosynthetic capacity may be enhanced simultaneously, so the F_v/F_m value would increase with the NO2- released by phytoplankton. Fundamentally speaking, the relationship between F_v/F_m and phytoplankton community structure in the natural sea area reflects the effects of different environmental conditions(such as light and nutrient salt) on the photosynthetic reaction mechanism of phytoplankton.(3). From the in situ study on photosynthetic characteristics of phytoplankton in winter in the West Pacific, we come to the conclusions as follows: in some high temperature, low nutrient and low productivity ocean area, the restriction of environmental factors inhibited the photosynthesis of phytoplankton, so the photosynthetic activity and carbon fixation ability of phytoplankton were decreased and this is one of the reasons for the low productivity of the ocean area; On transect DY, water layer with the maximum value of F_v/F_m was consistent with the Deep Chlorophyll Maximum(DCM) layer, which could not only protect the photochemical reaction center of phytoplankton from harm of intense light radiation, but also guarantee the contribution rate of DCM layer to the primary productivity of the whole water body.(4). The effects of different phosphorus(P) concentrations(0.36, 3.6, and 36 μmol/L corresponding to low-, middle-, and high-P concentration groups, respectively) and nitrogen(N)/P ratios on the growth and photosynthetic characteristics of Skeletonema costatum and Prorocentrum donghaiense were studied. For both species, the high-P(HP) concentration group showed the greatest algal density and highest specific growth rate. Changes in the maximum efficiency of photosystem II(F_v/F_m) were monitored under the various P and N/P conditions. The largest decrease in F_v/F_m was in the low-P(LP) group in S. costatum and in the HP group in P. donghaiense. There were high rapid light curves and photochemical quantum yields(ΦPS II) for S. costatum in the HP group, while the actual photosynthetic capacity was higher in P. donghaiense than in S. costatum in the MP group. Under the same P concentration and N/P ratio, P. donghaiense had a larger relative maximum rate of electron transport and higher ΦPS II values than those of S. costatum. Under eutrophic but relatively P-restricted conditions, P. donghaiense had higher photosynthetic activity and potential, which could cause this dinoflagellate to increasingly dominate the phytoplankton community in these conditions.