Characterisation and Quantification of the Fluxes of Particulate and Dissolved Nitrogen in the Unicellular Diazotroph Crocosphaera watsonii - Towards a Closed Nitrogen Budget
| Type | : | AP |
|---|---|---|
| Nature | : | Production scientifique |
| Au bénéfice du Laboratoire | : | Oui |
| Statut de publication | : | Publié |
| Année de publication | : | 2019 |
| Type de thèse | : | Thèse de Doctorat |
| Date | : | 08/11/2019 |
| Nombre de pages | : | - |
| Directeur de thèse | : | Sophie Rabouille |
| Université | : | Université Pierre et Marie Curie |
| Département académique | : | |
| Auteur | : | RANDALL Ben |
| DOI | : | - |
| URL | : | - |
| Abstract | : | Nitrogen (N) fixation, or diazotrophy, exists as a major source of biologically available N in the marine environment, affecting important processes such as the marine food web and the biological carbon (C) pump. Despite this, important fluxes into and out of the dissolved N phase , which inform the overall N budgets of individual diazotrophs, are poorly understood. This is especially true of recently discovered diazotrophs which may not function to previously established paradigms. One such diazotroph is the unicellular cyanobacteria Crocosphaera watsonii (UCYN- B), which is easily culturable and widespread throughout sub-tropical oceans. Here we attempt to characterise N fluxes consequent to diazotrophy for Crocosphaera, including the importance of fluxes of nitrate (NO3-), ammonium (NH4+), and dissolved organic N (DON). Furthermore, we aim to use our results to assess the accuracy of commonly used biological N2 fixation assays. We first assessed the use of NO3- by Crocosphaera. To do this, batch cultures of Crocosphaera were grown long term with NO3-, with measurements made to quantify the uptake NO3- and its effect on diazotrophy, culture growth and other important physiological parameters. In short, we found little uptake with no effect on the assessed parameters, including diazotrophy. We next focussed on flux of DON and NH4+ in continuous cultures regulated for culture conditions such as temperature, turbidity, and pH. In addition we targeted light availability as an important parameter. Between two culture conditions of sub-saturating and saturating light, we found an important increase in N acquisition, C acquisition and cell population growth rate in the saturating light condition. Furthermore, we found a significant uptake of DON over a 24h period, with a far more important uptake in the sub saturating light scenario (42% v.s. 7%). We also found greater flux of NH4+ into the medium in said scenario. When using an isotopic approach, we found roughly 2.5-3.5% of recently fixed N was present in the medium after 24h. Our assessment of the accuracy of commonly used methodology found that 15N2 incubation consistently underestimated N2 fixation while the acetylene reduction assay overestimated. Overall however, 15N2 incubations were more reliable, especially when factoring in fluxes of dissolved N, which is often uncontrolled for. Our findings represent new perspectives into the importance of fluxes of dissolved N to N budgets of Crocosphaera watsonii. |
| Mots-clés | : | - |
| Commentaire | : | Cofinancement Région PACA-GEOMAR Jury : Amel Latifi, Rapporteur Eric Achterburg, Rapporteur Aurelien Paulmier, Membre de jury Nathalie Vigier, Membre de jury Andreas Oschlies, Membre de jury Sophie Rabouille, Directrice de Thèse |
| Tags | : | PISCO |
| Fichier attaché | : | - |
| Citation | : |
Randall B (2019) Characterisation and Quantification of the Fluxes of Particulate and Dissolved Nitrogen in the Unicellular Diazotroph Crocosphaera watsonii - Towards a Closed Nitrogen Budget. Université Pierre et Marie Curie
|