Integrating the impact of global change on the niche and physiology of marine nitrogen-fixing cyanobacteria

Wrightson, Lewis, Yang, Nina, Mahaffey, Claire ORCID: 0000-0002-4215-7271, Hutchins, David A and Tagliabue, Alessandro ORCID: 0000-0002-3572-3634
(2022) Integrating the impact of global change on the niche and physiology of marine nitrogen-fixing cyanobacteria. GLOBAL CHANGE BIOLOGY, 28 (23). pp. 7078-7093.

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Marine nitrogen fixation is a major source of new nitrogen to the ocean, which interacts with climate driven changes to physical nutrient supply to regulate the response of ocean primary production in the oligotrophic tropical ocean. Warming and changes in nutrient supply may alter the ecological niche of nitrogen-fixing organisms, or 'diazotrophs', however, impacts of warming on diazotroph physiology may also be important. Lab-based studies reveal that warming increases the nitrogen fixation-specific elemental use efficiency (EUE) of two prevalent marine diazotrophs, Crocosphaera and Trichodesmium, thus reducing their requirements for the limiting nutrients iron and phosphorus. Here, we coupled a new diazotroph model based upon observed diazotroph energetics of growth and resource limitation to a state-of-the-art global model of phytoplankton physiology and ocean biogeochemistry. Our model is able to address the integrated response of nitrogen fixation by Trichodesmium and Crocosphaera to warming under the IPCC high emission RCP8.5 scenario for the first time. Our results project a global decline in nitrogen fixation over the coming century. However, the regional response of nitrogen fixation to climate change is modulated by the diazotroph-specific thermal performance curves and EUE, particularly in the Pacific Ocean, which shapes global trends. Spatially, the response of both diazotrophs is similar with expansion towards higher latitudes and reduced rates of nitrogen fixation in the lower latitudes. Overall, 95%-97% of the nitrogen fixation climate signal can be attributed to the combined effect of temperature on the niche and physiology of marine diazotrophs, with decreases being associated with a reduced niche and increases resulting due to a combination of expanding niche and temperature driven changes to EUE. Climate change impacts on both the niche and physiology of marine diazotrophs interact to shape patterns of marine nitrogen fixation, which will have important implications for ocean productivity in the future.

Item Type: Article
Uncontrolled Keywords: climate change, earth system models, elemental use efficiency, marine nitrogen fixation, microbial thermal fitness
Depositing User: Symplectic Admin
Date Deposited: 18 Nov 2022 10:42
Last Modified: 18 Jan 2023 19:43
DOI: 10.1111/gcb.16399
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