THE RELATIONSHIP BETWEEN ORGANIC NITROGEN AND THE CAROTENOID TO CHLOROPHYLL a RATIO IN FIVE FRESHWATER PHYTOPLANKTON SPECIES1

A linear relationship of positive slope was found between the ratios of organic nitrogen: chlorophyll a and total carotenoids: chlorophyll a in cultures of five freshwater phytoplankters as they recovered from N‐deficiency. This differed markedly from information in the literature for a marine diatom under similar conditions. This relationship in cultures of a freshwater diatom was not significantly different from one calculated from data in the literature for a N‐deficient natural population of marine diatoms. Therefore it is suggested that, under conditions of limiting nitrogen, the natural ratio of plant pigments can he used in conjunction with the nitrogen: pigment relationship to estimate the quantity of nitrogen in natural phytoplankton as distinct from other sources of particulate nitrogen in surface waters.