The Effect And Significance Of Phosphorus On Key Physiological And Ecological Process Of Pleurochrysis Sp. Under Eutrophic Conditions

Coccolithophores is the most important and widely distributed marine micro phytoplankton after diatoms and dinoflagellates in modern marine. It has calcified coccolith on the cell surface as the most significant character. Pleurochrysis sp. is common specie distributed in coastal area and aquaculture environments. Besides Emiliania huxleyi, Pleurochrysis sp. is the most frequently studied species. Because it has typical calcification closely related to carbon cycle and it is DMSP high-yield species, and it victimize the aquaculture object. Phosphorus is an important biological source element. Phosphate content in water directly influences the phytoplankton productivity. Also phosphorus is one of eutrophication elements. In this study, we take Pleurochrysis sp. as our research object. We studied phosphorus absorption characteristics during the population dynamics and analysed and discussed several key physiological ecology processes response under different phosphorus specieses and quantities and its ecological environment effect.CO1showed APA (alkaline phosphatase activity) enhance in the later at9th day. while there was a trace of phosphate in the medium. But CO2didn’t show any APA increase during the experiment. After a period of phosphate starvation, two Pleurochrysis sp. rapidly absorbed phosphate in water, and showed "extravagant absorption phenomenon". Compared to the phosphorus, nitrogen absorption was relatively stable. Meanwhile we found that cell calcification of the two Pleurochrysis sp. showed a cyclical change:calcification declined at the exponential phase, maintained stable at early platform phase, and increased at later platform phase. The change of APA was very similar with calcification trend.Based on the above results, we found that phosphorus linked more closely to several key physiological and ecological processes. Therefore we study further about the response characteristics of two Pleurochrysis sp. under different phosphorus specieses (ATP, glycerol phosphate sodium and KH2PO4) and different concentrations of KH2PO4. The results showed that organic phosphorus sources, especially ATP, could not only improve the biomass, but also significantly affect photosynthetic and calcification. As for photosynthesis, ATP not only increased the chlorophyll content but also activity. Chlorophyll fluorescence parameters, such as Ft and QY, were much higher than that of other experimental groups. But the ATP group calcification was far lower than other experimental group. The ATP group had not detected high APA. So we supposed that it should be absorbed directly, glycerol phosphate sodium’s contribution on population growth was less than ATP, but its alkaline phosphatase activity was high only less than the phosphorus deficiency. So it should be decomposed by AP (alkaline phosphatase) to form inorganic phosphorus before being absorbed.While the population growth was not obviously inhibited under phosphorus deficiency, chlorophyll content and activity were significantly reduced. Phosphorus deficiency has apparently decreased the photosynthesis efficiency but phosphorus strengthened cell calcification.Different phosphorus sources showed both similar and different effects on two Pleurochrysis sp. For example, ATP could improve the photosynthesis efficiency and reduce cell calcification of two Pleurochrysis sp but chlorophyll fluorescence parameters of CO1showed a certain relevance with different KH2PO4concentration. Ft and QY enhannced as KH2PO4concentration increasing. But CO2didn’t show the relevance.Two Pleurochrysis sp. showed higher Artemia lethal rate than hungry, which illustrated that both of them had certain physiological toxicity which was consistent with previous published results. But Artemia lethal rate of two Pleurochrysis sp. were different:CO1LD7211was higher than CO2. And Artemia lethal rate had a close relationship with phosphate specieses. Artemia lethal rate reduced under the condition of ATP and increased under phosphorus deficiency condition. DMSP content showed the same change:DMSP content decreased significantly under the condition of ATP and increased under phosphorus deficiency condition. But whether there is direct relationship between DMSP and Artemia lethal rate still need further research.