LIGHT MICROSCOPE OBSERVATIONS ON CYTOLOGICAL MANIFESTATIONS OF NITRATE, PHOSPHATE, AND SILICATE DEFICIENCY IN FOUR MARINE CENTRIC DIATOMS

SUMMARY Cytological changes induced by nitrate or phosphate limitation were reproducible and readily visible by phase contrast microscopy in Coscinodiscus wailesii, Ditylum brightwellii, Rhizosolenia hebetata f. semi‐spina, Skeletonema costatum, and Stephanopyxis turris. These effects included changes in chromatophore number and shape, pyrenoid location, and mitochondrial abundance and appearance. In S. costatum, a diatom containing only 1 chromatophore, only nitrogen‐deficient cells could be recognized. Silicate deficiency prevented cell division almost entirely. When a few cells did divide in the presence of low silicate, abnormalities in valve structure occurred in some cells. Cytological differences with N and P deficiency may permit a rough assessment of the physiological condition of the same or similar species in natural diatom communities.