Nickel limitation of nitrogen fixation in Trichodesmium

I show that the growth of Trichodesmium, the primary diazotrophic phytoplankton in tropical and subtropical oceans, can be limited by Ni availability in both trace metal‐defined culture media and natural seawater when the supply of Fe and P is sufficient. I further show that the increase of Ni concentrations elevates cellular superoxide dismutase (SOD) activities and nitrogen fixation rates, suggesting that NiSOD may be involved in the protection of nitrogenase from superoxide inhibition during photosynthesis in this nonheterocystous diazotroph.