Uptake of dissolved inorganic nitrogen and N2 fixation by Crocosphaera watsonii under climate change scenarios Umbricht, J. Filella, A. Klett, A. Vogts, A. /Benavides, Mar Voss, M. nitrogen fixation ocean warming ocean acidification nitrogen assimilation Crocosphaera minicosm experiment The response of N-2 fixation to projected future conditions in the ocean cannot be reliably predicted to date. We conducted a minicosm experiment with pre-acclimated cultures of the globally significant diazotroph Crocosphaera watsonii strain WH8501 ("Crocosphaera"). PH and temperature were altered simultaneously to match the RCP scenarios 4.5 and 6 and investigate a more realistic future scenario compared to studies that focus on changes of a single stressor only. The cell abundance and nitrogen metabolism of Crocosphaera was monitored over 5 days. Our results imply that Crocosphaera is able to simultaneously perform N-2 fixation and assimilate dissolved inorganic nitrogen (DIN, i.e., nitrate and ammonium) under all the conditions tested and implies a competition with non-diazotrophic phytoplankton for DIN, which should be further investigated. Using NanoSIMS analysis of single cells, our results point towards a preference for DIN assimilation over N-2 fixation under more acidic and warmer conditions. Overall, our results show that while the combined alteration of pH and temperature had a negative effect on the diazotroph's growth and N-2 fixation, Crocosphaera is likely to cope well with conditions in the future ocean. The high intra-population variability in nitrogen assimilation pathways may give this species the flexibility to quickly react to environmental changes. 2024 text https://www.documentation.ird.fr/hor/fdi:010091090 fdi:010091090 Umbricht J., Filella A., Klett A., Vogts A., Benavides Mar, Voss M.. Uptake of dissolved inorganic nitrogen and N2 fixation by Crocosphaera watsonii under climate change scenarios. 2024, 11, 1388214 [13 p.] EN MEDITERRANEE