Phytotransferrin was first described in 2018, and phytotransferrin-encoding gene sequences can be found in most major phytoplankton groups. However, the phytotransferrin mechanism has only been characterized in a model organism, and iron-carbonate co-limitation has never been documented in the environment. To fill these knowledge gaps, project IRONBIND set out to answer three fundamental questions: How widespread is the phytotransferrin mechanism? Can the effect of carbonate on iron uptake be measured in the environment? And if there is an effect, what are the ramifications for climate change and the global carbon cycle?
To determine whether carbonate co-limited iron uptake is common, IRONBIND collaborated with the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) to measure iron uptake rates in environmentally relevant species of Southern Ocean phytoplankton, including diatoms, coccolithophores, cryptophytes, chlorophytes and Phaeocystis. All tested phytoplankton showed a negative influence of low carbonate on iron uptake rates, particularly in the absence of light. The effect was consistent whether synthetic or natural iron chelators were evaluated. To determine whether this effect could be detected in the natural marine environment, IRONBIND collaborated with the Department of Environmental Affairs, Republic of South Africa, to participate in the SCALE expedition to the spring ice edge in the Southern Ocean. IRONBIND was able to confirm that carbonate co-limitation could be detected in iron uptake rates from natural populations of marine phytoplankton, and that acidification has an effect on phytoplankton growth rates. The Covid-19 pandemic of 2020 has delayed some of the analytical work; however, IRONBIND is currently preparing the dataset for modelling to provide broader ecological and biogeochemical context. These results will be archived in the PANGAEA Data Publishing portal for Earth & Environmental Science, hosted by the Alfred Wegener Institute and available to the public. Additionally, the results will be disseminated at the 2021 Ocean in a High CO2 World conference in Lima, Peru, and are being prepared for publication in a high-impact, broad interest journal.
