Closing the gaps in freshwater diazotrophy across the global ecospace

New evidence and previous estimations indicate that dinitrogen fixation by diazotrophs may play a central role in the freshwater biosphere along the ecological scales. And yet little is currently known on freshwater DIAZOTROPHY, namely the diversity, abundance and N₂ fixation rates across the global freshwater ecospace, while even less is known on the environmental factors that control them. This research closes the knowledge gaps related to freshwater diazotrophy: from the abiotic factors that control diazotrophs abundance, diversity, and activity at the global scale. Achieving this global objective was done by sending a custom kit to 91 research groups from 68 countries that sampled 230 freshwater locations across the world. These samples were analysed for diazotrophs abundance, diversity and N₂ fixation rates as well as organic carbon, nitrogen and various nutrients. Sampling across the world was carried during April-May 2023, thus springtime at the northern hemisphere and autumn at the southern hemisphere. A few unicellular diazotrophs hotspots (>15 x10⁷ cells L^-1) were apparent across the freshwater ecospace. Corresponding N₂ fixation rates were relatively low (<4 nmol N L^-1 d^-1) at the northern hemisphere, yet few regions exhibited high values (>50 nmol N L^-1 d^-1) were apparent at Northern US and Spain. Alpha diversity was variable (<7.5), with high % of NCDs. Overall, this global research generates new insights on the environmental factors that control N fixation and its significance of freshwater diazotrophy to new N production across the freshwater ecospace.

Presentation Preference: Oral

Primary Presenter: Edo Bar-Zeev, Ben Gurion University of the Negev (edobarzeev@gmail.com)

Authors:

Edo Bar-Zeev, Ben Gurion University of the Negev  (edobarzeev@gmail.com)