We cultured different-sized fractions of dominant phytoplankton species,Skeletonema costatum,Chaetoceros curvisetus,and Thalassiosira nordenski ldii,collected in different sea areas in various seasons,and measured and compared their C,N,P,Si contents.The N content of these species is similar,while the C,P,and Si contents of S.costatum from eutrophic Changjiang (Yangtze River) estuary are higher than those from Jiaozhou Bay (JZB),particularly the content of Si.The C,N,P,and Si contents of cultured phytoplankton in JZB increase with size fraction augmentation,and the percentages of C,N,and P follow the same trend,while the percentage of Si remain constant.Moreover,S.costatum from small-sized fraction assimilated Si more easily than C.curvisetus and T.nordenski ldii,which is explained by the dominance of S.costatum under the conditions of low SiO 3-Si concentration in JZB.The C,N,P,and Si contents of cultured S.costatum collected during summer and winter are higher,which is consistent with the phytoplankton blooming seasons in JZB.The SiO 3-Si concentration of seawater during spring restrain the growth of phytoplankton,supported by the fact that the N,P,and Si contents and their ratios in cells of cultured S.costatum are low in spring season.
