Effect of combined action of light and silicon depletion on Asterionella formosa Hass

Summary

Silicon depletion in fresh waters is of ecological interest because it is recognized as a factor determining the close of spring maxima of diatoms. To study the lethal effect of light at silicon depletion, cultures of Asterionella grown at about 3 klx and alternate light and dark periods of 12 hours were used. It is found, by sampling after the dark periods, that the start of the Si-depleted phase is revealed not only by the end of cell increases, but also by an enhanced ratio caroteneïds: chlorophyll a. The relatively short stationary phase, characterized by more or less constant cell numbers, is followed by a phase in which the number of “living” cells decreases, pigment is broken down and “silicon” is detectable in the medium in increasing amounts. Besides, there is evidence that Asterionella cells of Si-depleted cultures have a faster rate of sinking than cells grown at sufficient Si-concentration.