Cell death in three marine diatom species in response to different irradiance levels, silicate, or iron concentrations

Abstract

The effects of light, silicate, or iron limitation on cell death rates and the accompanying effects on growth rates and photosynthetic efficiencies were investigated for 3 species of marine diatoms, Chaetoceros brevis, Chaetoceros calcitrans and Thalassiosira antarctica. Cell death rates were based on changes in time of the percentage dead cells using the SYTOX Green membrane per- meability assay. The death rates increased with decreasing irradiance levels and silicate concentra- tions for T. antarctica. In contrast, the cell death rates were hardly affected by low irradiances or sili- cate for C. brevis and C. calcitrans. Iron limitation experiments did not affect algal death rates significantly in the species tested. Growth rates under limiting conditions decreased from 0.6-0.4 to 0.2-0.1 d -1 , and only under low light conditions did growth halt completely. Photosynthetic efficien- cies did not always co-vary with cell death rates and were shown to be a sensitive indicator of light and iron limitation, but not of silicate limitation. This is the first detailed study providing data on diatom cell death under different growth-limiting conditions. The differential response in cell death rates indicates irradiance as a determining factor in diatom species succession and distribution.