| In recent decades,the frequency and intensity of algal blooms in the sea have increased because of climate change and eutrophication mainly resulting from human activity.The blooms especially of dinoflagellates have also become increasingly frequent in China,causing devastating impacts on the marine ecosystem,local fisheries industry,and even health problems in humans.Nutrients are the most important limiting factors for the growth of phytoplalkton.So3 understanding of mechanism of nutrient uptake and assimilation by dinoflagellates is ecologically significant.Here,two typically harmful dinoflagelltes,Karenia mikimotoi and Noctiluca scintillans,were chosen to exprlore the effects of nutrients on algal growth as well as bloom formation.Firstly,we explored the availability of different phosphorus and molecular mechanism of dissolved organic phosphorus(DOP)utilization by K.mikimotoi using suppression subtractive hybridization(SSH)combined with 454 pyrosequencing.The results showed that K mikimotoi was able to utilize DOP such as ATP and G6P as the sole P source efficiently.A nucleotidase instead of alkaline phosphatase was used to hydrolyze ATP.The three Pi groups of ATP could be cleaved in sequence based on the ambient P stress.Conversely,K.probably took in the whole G6P.Besides,we compared and analyzed the growth of K,mikimotoi under different concentrations of N vs P.Our results indicated N limitation(N:P<16:1)slowed down the growth of this species.Correspondingly,two kinds of nitrogen transporter showed higher expression.Also,effciency of carbon assimilation changed under N stress.We also studied the characteristics of nutrient uptake and metabolism as well as species succession during different stages of dinoflagellate blooms at sea based on our laboratory work of DOP utilization.(1)During the bloom in the sea near Xiapu,China in 2017,the dominant species were K.mikimotoi and Prorocentrum donghaiense.Our data showed that dissolved inorganic nutrients(DIN)are preferred sources for dinoflagellates,but when DIN concentrations are extremely low,DOP will be very vital to support algal growth.The rate of different nutrients such as N and P also can regulate the formation of bloom as well as community stucture of phytoplankton.Lower rate of N and P(<16)contributed to the growth of dinoflagellate.Sexual reproduction of K.mikimotoi,revealed by cell cycle analysis,was likely to give this species competition advantage against other phytoplankton.(2)An investigation of green Noctiluca scintillans bloom was conducted along the coast of Oman.Our study showed diatom population decreased drastically during Noctiluca bloom,but recovered quickly once the bloom vanished,indicating feeding diatom might be a very important way to aquire nutrients for the formation and presistance of the Noctiluca bloom.We also detected more nutrients and less oxygen during the bloom,which probably contributed to the growth of Noctiluca.Further laboratory experiments indicated that Noctiluca cells released these nutrients,which could fuel growth of other phytoplankton species such as diatom,the preferred food of Noctiluca.Physiological measurements and advanced molecular techniques were applied to this study.Combining laboratory work and field investigation,we gained understanding on the role of nutrients in bloom formation and species succession.Our findings will be helpful for us to know more about harnful algae blooms and the detrimental effects of nutrient discharge to the sea on the marine ecosystem.Also,our studv,especially the construction of transcriptomic libraries,provides useful resources for future research. |
PDF Full Text Request