Unicellular Cyanobacterial Distributions Broaden the Oceanic N ₂ Fixation Domain

TLDR

Oceanic nitrogen fixation sustains global marine productivity and balances CO₂ export to the deep ocean, and was previously thought to be driven solely by the filamentous cyanobacterium Trichodesmium. The study investigates how newly discovered unicellular open‑ocean cyanobacteria contribute to global nitrogen fixation and how their distribution and activity compare to Trichodesmium. Using data from the southwest Pacific Ocean, the authors incorporated these findings into models to refine estimates of global oceanic nitrogen fixation and carbon sequestration. The unicellular nitrogen‑fixing cyanobacteria UCYN‑A and Crocosphaera watsonii exhibit distinct ecophysiologies and oceanic distributions, differing from each other and from Trichodesmium. The abstract.

Abstract

Oceanic Nitrogen Fixation Nitrogen fixation in the oceans is important in sustaining global marine productivity and balances carbon dioxide export to the deep ocean. It was previously believed that marine nitrogen fixation was due to a single genus of filamentous cyanobacteria, Trichodesmium . The recent discovery of unicellular open-ocean cyanobacteria has raised the question of how they contribute to global ocean nitrogen fixation and how they compare in distribution and activity to Trichodesmium . Using data collected from the southwest Pacific Ocean, Moisander et al. (p. 1512 , published online 25 February) show that the unicellular nitrogen-fixing cyanobacteria (UCYN-A and Crocosphaera watsonii ) have distinct ecophysiologies and distinct oceanic distributions from each other, and from Trichodesmium . These data can be incorporated into models to retune estimates of the global rates of oceanic nitrogen fixation and carbon sequestration.