1. Department of Botany, University of British Columbia, Vancouver BC Canada V6T 1Z4
2. Department of Botany and Department of Earth and Ocean Sciences, University of British Columbia, Vancouver BC Canada V6T 1Z4
3. Present addresses: NIWA Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand (R.F.S.); Atmospheric, Marine & Coastal Environment (AMCE) Program, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (P.J.H.)

Correspondence to: Robert F. Strzepek^1,3 Correspondence and requests for materials should be addressed to R.F.S. (Email: roberts@alkali.otago.ac.nz).

Abstract

Diatoms are a key taxon of eukaryotic phytoplankton and a major contributor to global carbon fixation¹. They are ubiquitous in the marine ecosystem despite marked gradients in environmental properties, such as dissolved iron concentrations, between coastal and oceanic waters. Previous studies have shown that offshore species of diatoms and other eukaryotic algae have evolved lower iron requirements to subsist in iron-poor oceanic waters, but the biochemical mechanisms responsible for their decreased iron demand are unknown^{2, 3}. Here we show, using laboratory-cultured model species, a fundamental difference between a coastal and an oceanic diatom in their photosynthetic architecture. Specifically, the oceanic diatom had up to fivefold lower photosystem I and up to sevenfold lower cytochrome b₆f complex concentrations than a coastal diatom. These changes to the photosynthetic apparatus markedly decrease the cellular iron requirements of the oceanic diatom but not its photosynthetic rates. However, oceanic diatoms might have also sacrificed their ability to acclimate to rapid fluctuations in light intensity—a characteristic of dynamic and turbid coastal waters. We suggest that diatoms, and probably other eukaryotic algal taxa, exploited this difference in the underwater light climate between oceanic and coastal waters, enabling them to decrease their iron requirements without compromising photosynthetic capacity. This adaptation probably facilitated the colonization of the open ocean by diatoms, and contributes to their persistence in this iron-impoverished environment.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.