THE EFFECT OF IRON NUTRITION ON PHOTOSYNTHESIS AND NITROGEN-FIXATION IN CULTURES OF TRICHODESMIUM (CYANOPHYCEAE)

Cultures of Trichodesmium NIBB 1067 were grown in the synthetic medium AQUIL with a range of iron added from none to 5 × 10−7 M Fe for 15 days. Chlorophyll‐a, cell counts, and total cell volume were two or three times higher in medium with 10−7 M Fe than with no added Fe. Oxygen production rate per chlorophyll‐a was over 60% higher with higher iron. Increased iron stimulated photosynthesis at all irradiances from about 12–250 μE · m−2· s−1. Nitrogen fixation rate, estimated from acetylene reduction, for 10−7 and 10−8 M Fe cultures was approximately twice that of the cultures with no added Fe. The range of rates of O2 production and N2 fixation in cultures at the iron concentrations we used were similar to the rates from natural samples of Trichodesmium from both the Atlantic, and the Pacific oceans. This similarity may allow this clone to be used, with some caution, for future physiological ecology studies. This study demonstrates the importance of iron to photosynthesis and nitrogen fixation and suggests that Trichodesmium plays a central role in the biogeochemical cycles of iron, carbon and nitrogen. Copyright © 1990, Wiley Blackwell. All rights reserved