Effect Of Iron,Phosphorus And Irradiance On Growth Of Three Kind Of Phytoplankton

Red tide has become one of the several great marine disasters for its severe harm to marine economy in China.Three kinds of phytoplankton called Prorocentrum micans Ehrenberg,Cryptomonas sp.,and picophytoplankton diatom are selected as culture species,which widely distribute in coastal regions of China.The change of cell density,growth rate,cell microstructures,nutrient uptake and assimilation is researched on different irradiance and concentrations of iron and phosphorus in culture conditions.Results show as follows:In iron limitation condition,the growth rate and maximum cell density of the selected phytoplankton are influenced distinctly,especially when iron concentration is less than 10nmol L^-1.The influence on Prorocentrum micans Ehrenberg is the most obvious,which is followed by Cryptomonas sp.,and picophytoplankton diatom is the slightest.The microstructures of Prorocentrum micans Ehrenberg and Cryptomonas sp.vary obviously during longtime iron starvation,but picophytoplankton diatom does not distinctly.Firstly,the microstructure of chloroplast membrane begins to destroy and gradually vanish.Then, many twisted and metamorphosed Chloroplast is observed.Because structures of membrane of other organs break,the subcell microstructures boundary become indistinct,even cell nucleus and other organs vanish.Nutrient uptake and assimilation of Prorocentrum micans Ehrenberg and Cryptomonas sp.is influenced distinctly, when iron is deficient.At the same time manganese replaces iron to take relevant physiological activity.Phosphorus exerts a marked impact on phytoplankton growth.All three kinds of phytoplankton cease growing in the absence of phosphorus.The cell density of Prorocentrum micans Ehrenberg will increase with enhancing of phosphorus concentration in culture medium.Phosphorus consistency has an important impact on Cryptomonas sp.absorbing some trace elements.When phosphorus consistency in culture medium is 0.5μmol L^-1,the content of manganese,nickel,cobalt,zinc,and copper of Cryptomonas sp.is distinctly less than that when phosphorus consistency in culture medium is 5μmol L^-1and 15μmol L^-1.The optimum irradiance of three kinds of phytoplankton is different,of which Prorocentrum micans Ehrenberg is the highest,Cryptomonas sp.is slightly less and picophytoplankton diatom is the lowest.Under low irradiance,the chloroplast content increase obviously.In the co-limitation of the irradiance and iron condition,while phytoplankton is cultured at irradiance less than 30μE m^-2s^-1,Cryptomonas sp.growth rate is affected by irradiance more than iron.But while irradiance is more than 60μE m^-2s^-1,iron limitation becomes obviously.Especially when irradiance approaches to the saturated irradiance of Cryptomonas sp.,iron limitation becomes most obviously. It is observed during interbreeding culture that picophytoplankton diatom tend to predominate under low irradiance,whereas under high irradiance Cryptomonas sp. and Prorocentrum micans Ehrenberg are dominant.These results suggest that irradiance may regulate the composition of phytoplankton assemblage in marine ecosystem.A number of picophytoplankton diatom transform to spores after cultivated at irradiance less than 1μE m^-2s^-1for 60 days,while this phenomenon is not observed during cultured Prorocentrum micans Ehrenberg and Cryptomonas sp.Irradiance can obviously affect the phytoplankton growth and the nutrient uptake and assimilation. When Irradiance is 10μE m^-2s^-1,the uptake and assimilation of Al by picophytoplankton diatom is 70 times,Cryptomonas sp.is 80-100 times,in terms of the aluminum concentration in the culture solution.When irradiance is from 10μE m^-2s^-1to 200μE m^-2s^-1,the enrichment of lead decreases with irradiance enhancing. The biggest enrichment of Prorocentrum micans Ehrenberg is 160 times, Cryptomonas sp.is about 150 times and picophytoplankton diatom is about 80 times.The results are of implications for well understanding the limitation of iron, phosphorus,and irradiance in the control of marine primary production,and may provide novel insight for understanding the mechanisms of phytoplankton bloom and important theoretical and practical implications for seeking efficient pathways to control the occurrence of red tides.