Preprints
https://doi.org/10.5194/egusphere-2024-775
https://doi.org/10.5194/egusphere-2024-775
19 Mar 2024
 | 19 Mar 2024
Status: this preprint is open for discussion.

Effects of CO2 on the nitrogen isotopic composition of Trichodesmium and Crocosphaera

Zuozhu Wen, Ruotong Jiang, Tianli He, Thomas Browning, Haizheng Hong, and Dalin Shi

Abstract. Biological nitrogen (N2) fixation is the main input of fixed nitrogen to ecosystems on Earth. Nitrogen isotope fractionation during this process is a key parameter for understanding the nitrogen cycle, however, relatively little is known about its regulatory mechanisms. Here we examine the effects of varying CO2 concentrations on biomass δ15N signatures of the cyanobacterial diazotrophs Trichodesmium erythraeum and Crocosphaera watsonii. We show that these organisms produce biomass up to ~3 ‰ lower in δ15N under either decreased (~180 µatm) or elevated (~1400 µatm) CO2 concentrations in comparison to modern levels (~380 µatm). Our results pointed towards changes in nitrogenase enzyme efficiency in response to CO2 perturbations impacting isotopic fractionation during N2 fixation and thus the biomass δ15N. This study contributes to an improved interpretation of the observed fluctuations in the δ15N records, and thus the past nitrogen cycle on Earth.

Zuozhu Wen, Ruotong Jiang, Tianli He, Thomas Browning, Haizheng Hong, and Dalin Shi

Status: open (until 18 May 2024)

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Zuozhu Wen, Ruotong Jiang, Tianli He, Thomas Browning, Haizheng Hong, and Dalin Shi
Zuozhu Wen, Ruotong Jiang, Tianli He, Thomas Browning, Haizheng Hong, and Dalin Shi

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Short summary
The isotope effect of biological N2 fixation is a key parameter for understanding the nitrogen cycle, however, little is known about its regulatory mechanisms. Here we show for the first time that CO2 exerts important controls on the N isotopic composition in diazotrophic cyanobacteria Trichodesmium and Crocosphaera, through the controls on nitrogenase enzyme efficiency. This study provides insights into understanding the fluctuations of δ15N records, and thus the past nitrogen cycle.