Effects of different Si concentrations on the growth and chlorophyll fluorescence of Chaetoceros gracilis and Phaeodactylum tricornutum

In this experiment, the effects of different Na2SiO3-Si concentrations (0, 12, 24, 48, 96 and 384 μmol/L) on the cell densities, chlorophyll contents and maximal photochemical efficiency of PSⅡ (Fv/Fm) of two marine diatoms (Chaetoceros gracilis and Phaeodactylum tricornutum) were studied. The algae were obtained from the Microalgae Culture Center (MACC), Ocean university of China. The experiment was carried out on the conditions of temperature 23±1 ℃, salinity 31, and light intensity 100 μmol/m2·s. One-way analysis of variance showed that Si produced significant effects on the growth and photosynthesis of the two diatoms. For C. gracilis, all of cell densities, chlorophyll contents and Fv/Fm increased with the increase of Si concentration at first, and then decreased with the increase of Si concentrations after reaching the highest values at the concentration of 96 μmol/L Si. With regard to P. tricornutum, the highest values appeared at the concentration of 384 μmol/L Si on day 7 for Fv/Fm, and day 3 for chlorophyll contents and cell densities. Multiple comparison tests showed that the optimal Si concentrations for the growth and photosynthesis of C. gracilis and P. tricornutum were 96 and 384 μmol/L, respectively.