Study On The Response Of Metal Element Contents In Marine Phytoplankton To Nutrient Levels In Seawater

Marine phytoplankton is an important carrier in metal element cycles.Theelement contents in phytoplankton samples deffer from the species, biomass, primaryproductivity as well as other environmental factors. Element contents ofphytoplankton are important parameters which indicate concentration and migrationof metals in the sea. Nutrient level of seawater is an important factor not only to thegrowth rate but also influencing the metal content of phytoplankton. Therefore, studyon the element composition of marine phytoplankton varying with the nutrient levelhas been significant for sedimentation and biogeochemical cycle of metal elements.Three species, i.e., Skeletonema costatum (Greville) Cleve; Platymonassubcordiforus; Phaeodactylum were choosen for batch culture experiments, whichwere carried out under changing nitrogen and phosphorus level with fixed N:P ratio,changing nitrate concentration with fixed phosphate, and changing phosphateconcentration with fixed nitrate. The growth curve, specific growth rate, dry weightand chlorophyll contnent were checked to confirm the repeatibilty of the cultureexperiment. The cultured phytoplankton samples were decomposed for metalelements and phosphorus determination. Main results of these experiments are shownas follows:(1) With the increasing nutrient level under a fixed N/P ratio, the contents of Fein Skeletonema costatum and Phaeodactylum reduced, while that in Platymonassubcordiforus was constant. The contents of Zn in the three algae decreased. Thecontents of Cu in Skeletonema costatum and in Platymonas subcordiforus increased atfirst and then decreased, and that in Phaeodactylum increased. The contents of Mn inthe Skeletonema costatum and Phaeodactylum decreased and that in the Platymonassubcordiforus increased at first and then decreased. The contents of Ca were reducedin the three kinds of algae decreased with the increasing nutrient level.(2) With the increasing nitrate concentrations under a fixed phosphateconcentration, the contents of Fe in Skeletonema costatum, Platymonas subcordiforusand Phaeodactylum descreased and the contents of Cu increased at first and then decreased. The contents of Mn in the Skeletonema costatum and Phaeodactylumdescreased while that in Platymonas subcordiforus increased first and then decreasedThe Ca contents in Phaeodactylum decrease at first and increased afterwards.(3) With the increasing phosphate concentrations under a fixed nitrateconcentration, the content of Fe in three kinds of algae decreased at first and thenincreased, while the contents of Cu in Skeletonema costatum and Platymonassubcordiforus increased at first and then decreased. The content of Mn in Skeletonemacostatum and Phaeodactylum decreased at first and then increased. The contents of Znin Skeletonema costatum and Phaeodactylum decreaseed, and that in Platymonassubcordiforus increased at first and then decreased.The main conclusions are drawn as follows according to the change of metalcontents in phytoplankton samples:1. The response of metal element contents in algae to the changing nutrients hadtwo scenarios:(1) Algae has a strong absorbing ability to some metals and the ability is notaffected by the nutrient level; algae body has higher metal content under the conditionof nutrient limitation. The Fe, Mn, Zn in Skeletonema costatum and Phaeodactylumbelong to this situation.(2) Nutrient deficiencies may limit the absorbtion of certain metals by algae; themetal content in algae body is lower under the condition of nutrient limitation. Theabsorbtion of Cu, Mg in Skeletonema costatum, Platymonas subcordiforus andPhaeodactylum and the absorbtion of Mn in Platymonas subcordiforus belong to thiscase.2The uptake of metals in Platymonas subcordiforus were different from twokinds of diatom: the content of Fe in the algae body was constant and had no effect ofnutrition level; nitrate restrictions affect the absorption of Mn by algae body;Phosphate limit had a certain impact to the absorption of Zn element.3It was found that most of the metals has both intracellular components andextracellular adsorption that the experiments of cleaning algae body to Skeletonemacostatum, most of the elements is given priority to with intracellular absorption.4The comparison of metal elements in phytoplankton cultured and phytoplanktonin the network: the contents of Fe, Mn in laboratory cultures of algae body of contentare higher than that of the net in marine phytoplankton, the contents of Zn and Cumetals net by phytoplankton are higher, and it is ralated to the differences in environmental condition and phytoplankton species between phytoplankton culturedand phytoplankton in the network.