| Eighteen common taxons of phytoplankton were investigated to determine the relationship between cell volume and their contents of carbon, nitrogen and chlorophyll a. Firstly, the morphological characteristics of eighteen taxons were observed using a Nikon ECLIPSE TE2000-U optical microscope so that cell-geometry analogous models were built appropriately. From these models, the resulting cell volumes for each phytoplankton can be calculated by microscope measurement of distances including cell length, width or diameter, breadth. Furthermore, cell carbon and nitrogen content was determined using a CHN analyzer, cell chlorophyll a content was determined using a Turner Design analyzer. Then the relationships between carbon, nitrogen and chlorophyll a contents and cell volume could be established and analyzed.A set of cell geometric models is suggested as a practical and accurate method for calculating phytoplankton cell volumes. In the present study, eight geometric models were constructed for eighteen species belonging to five phyla while formulas of cell volumes were determined. A. tamarense, A. offline, P. reticulatum, Chlorella sp., I. galbana and Dicrateria sp. were constructed as sphere. A. sanguinea, A. carterae, P. donghaiense, P. minimum, P. gracile were constructed as ellipsoid. G. spinifera was constructed as cone and half sphere. L. polyedra was constructed as two cones. S. costatum was constructed as cylinder and two half sphere. T. rotula was constructed as cylinder. C. curvisetus was constructed as prism on elliptic base P. helgolandica and H.akashiwo were both constructed as prolate spheroid. So cell volume of each taxon could be determined. The results showed that large differences were observed among the ten dinoflagellates, three diatoms and other five algaes in cell volume. And the range of cell volumes of dinoflagellates were from 2.97×102μm3 (Amphidinium carterae) to 4.50×104μm3 (Akashiwo sanguinea). The range of cell volumes of three diatoms were from 1.55×102(S. costatum) to 5.74×103μm3(T. rotula). The cell volume of H.akashiwo among other five algaes was the greatest (3.91×102μm3), next P. helgolandica(3.60×102×m3) andⅠ. galbana(53.57μm3) and Dicrateria sp. (56.74μm3), however, the cell volume of Chlorella sp. was the lowest(13.43μm3).Large differences were observed among the ten dinoflagellates in cell carbon, nitrogen and chlorophyll a contents. A. carterae had the lowest carbon and nitrogen contents (60.18 pg·cell-1,12.71 pg·cell-1), while G. spinifera had the greatest carbon and nitrogen contents (1993.64 pg·cell-1,395.63 pg·cell-1). A. tamarense had the lowest chlorophyll a (1.26 pg·cell-1) while L. polyedra had the greatest chlorophyll a (21.45 pg-cell-1). And A. sanguinea had the lowest carbon, nitrogen and chlorophyll a contents per unit volume(0.042 pg·μm-3,0.009 pg·μm-3,0.0004pg·μm-3) while P. minimum had the greatest carbon and nitrogen contents per unit volume(0.213 pg·μm-3,0.053pg·μm-3) and A. carterae had the greatest chlorophyll a content per unit volume.Among the diatoms, S. costatum had the lowest carbon, nitrogen and chlorophyll a contents (5.37 pg·cell-1,1.42 pg·cell-1 and 0.205 pg·cell-1), on the contrary, T. rotula had the greatest carbon, nitrogen and chlorophyll a contents (299.11 pg·cell-1,142.32pg·cell-1 and 6.33 pg·cell-1). And T. rotula also had the greatest carbon and nitrogen content per unit volume(0.052pg·μm-3,0.025 pg·μm-3) while S. costatum had the lowest ones(0.035pg·μm-3, 0.009 pg·μm-3). But S. costatum had the greatest chlorophyll a content per unit volume(0.0013 pg·μm-3), C.curvisetus had the lowest one(0.0003 pg·μm-3).For other five algae, the carbon,nitrogen and chlorophyll a contents per cell of H.akashiwo were greatest(194.13 pg·cell-1,45.82 pg·ceH-1 and4.76 pg·cell-1), next P. helgolandica andⅠ. galbana and Dicrateria sp., the carbon,nitrogen and chlorophyll a content per cell of Chlorella sp. were lowest(2.71 pg·cell-1,0.55 pg·cell-1 and 0.01 pg·cell-1). Similarly, H.akashiwo had the greatest carbon,nitrogen and chlorophyll a contents per unit volume(0.498 pg·cell-1,0.117 pg·cell-1 and 0.0123 pg·cell-1) whileⅠ. galbana had the lowest carbon and nitrogen contents per unit volume(0.123 pg·μm-3,0.02 pg·μm-3), and Chlorella sp. had the lowest chlorophyll a content per unit volume(0.0008 pg·μm-3).It was found significant linear relationship between carbon and both nitrogen and chlorophyll a contents of ten dinoflagellages, three diatoms and other five algaes (P<0.0001).In order to allow conversion among cell volume, carbon, nitrogen and chlorophyll a in the marine ecology field, it is important to establish regression equations between these parameters. It was found more appropriate analyze these relationships by logarithmic models due to the wide range of cell volume, cell carbon and nitrogen contents in agreement with Verity et al (1992).In the present study, the cell volume thus determined from the dinoflagellates, positive linear distances correlated to their carbon, nitrogen and chlorophyll a contents per cell significantly (P<0.0001), however, negative linear distances correlated to their carbon, nitrogen and chlorophyll a contents per unit volume significantly (P<0.0001). Therefore, the results indicated that carbon, nitrogen and chlorophyll a contents both per cell and per unit volume were not constants and carbon, nitrogen and chlorophyll a contents per cell increased with cell volume increasing, but carbon, nitrogen and chlorophyll a contents per unit volume decreased with cell volume increasing. So the smaller cells contained more carbon, nitrogen and chlorophyll a contents.Different from dinoflagellates, the cell volume thus determined from both the diatoms and other algaes positive linear distances correlated to their cell carbon, nitrogen and chlorophyll a contents significantly (P<0.0001), which indicated that the bigger cells contained more carbon, nitrogen and chlorophyll a contents.Effect of temperature on growth, cell volume and cell biochemical composition for Heterosigma akashiwo Hada and Alexandrium tamarense (Lebour) Balech were studied.The results showed that temperature had significant effects on growth, cell volume, cell biochemical composition, C:Chla and N:Chl a of H, akashiwo Ten to thirty temperature were all suitable for normal growth of H. akashiwo. The highest growth rate (0.49d-1) was observed at 25℃, which was the optimum temperature for growth of H. akashiwo. Cell volume of H. akashiwo tended to significantly decreased firstly (10℃～25℃) and then increased (25℃～30℃) with increasing temperature, which was the greatest at 10℃(823.89μm3) and the least at 25℃(387.98μm3). Analysis indicated that there was a negative correlation between Log(cell volume) and Log(growth rate) of H. akashiwo(P<0.05). Cell carbon and nitrogen contents of H. akashiwo were determined significantly decreased to some extent, however, cell carbon and nitrogen contents per unit volume of H, akashiwo were determined significantly changing like single-peak type with temperature increasingly. Chlorophyll a content per cell and per unit volume changed consistently with temperature increasingly. Result indicated that cell C:Chla and N:Chla of H, akashiwo decreased firstly and then increased with increasing temperature, which was the greatest at 10℃,69.98 and 2.78 respectively, the least at 25℃,27.05 and 5.67 respectively.The results showed that temperature had significant effects on growth, cell volume, cell biochemical composition, C:Chla and N:Chl a of A. tamarense.20℃was the optimum temperature for growth of A. tamarense. Cell volume of A. tamarense tended to significantly decreased firstly and then increased with increasing temperature, which was the greatest at 10℃(15406.50μm3) and the least at 20℃(8170.38μm3). Analysis indicated that there was a negative correlation between Log(cell volume) and Log(growth rate) of A. tamarense (P<0.05). Carbon and nitrogen contents per cell of A. tamarense were determined significantly decreased firstly and then increased gradually, on the contrary, cell carbon and nitrogen contents per unit volume of A. tamarense were determined significantly increased firstly and then decreased with temperature increasing from 10℃to 25℃. Results indicated that cell C:Chla and N:Chla of A. tamarense decreased firstly and then increased with increasing temperature, which was the greatest at 30℃,262.01 and 62.03 respectively, the least at 20℃,163.05 and 49.31 respectively. |
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