Effects of urea concentration in supporting growth of certain marine microplanktonic algae

Abstract

The effects of a range of concentrations of urea, supplied as sole nitrogen source for growth, were tested on eight assorted species of marine microplanktonic algae in axenic culture. Five species showed ready growth response to urea at low concentration, but a Porphyridium strain required considerable adaptation and a high threshold concentration for successful growth, whilst Chlamydomonas palla and Cyclotella cryptica failed to grow over the entire concentration range. Higher concentrations improved growth and pigmentation of species having difficulties in assimilating urea, and generally supported excellent growth of all species with any potential to utilize urea. The highest concentration tested (12·5 mM) was not inhibitory to growth, except in the case of a cryptomonad (Rhodomonas lens) which showed sudden autolysis after an initial phase of accelerated growth. It was inferred that phytoplankton potential for urea utilization may be broadly divided into three nutritional types of taxonomically-unrelated species, based on characteristic threshold concentrations and adaptation requirements for successful growth.