Mechanistic understanding of diazotroph aggregation and sinking: “A rolling tank approach” - Université de Bretagne Occidentale Access content directly
Journal Articles Limnology and Oceanography Year : 2023

Mechanistic understanding of diazotroph aggregation and sinking: “A rolling tank approach”


Diazotrophs are ubiquitous in the surface (sub)tropical ocean, where they sustain most new primary produc-tion. Several recent studies also report the presence of diverse cyanobacterial diazotrophs in the mesopelagicand bathypelagic ocean, suggesting that they gravitationally sink, potentially supporting organic matter exportand the biological carbon pump. Yet, the mechanisms leading to their export are not elucidated. Here, we simu-lated the sinking of diazotrophs in the water column by using rolling tanks, and measured the aggregationcapacity and sinking velocities of four globally distributed strains having different sizes, shapes, and abilities toproduce transparent exopolymer particles (TEP): twofilamentous diazotrophs (Trichodesmium erythraeum,Calothrixsp.) and two unicellular cyanobacterial diazotrophs (UCYN-B,Crocosphaera watsonii) and (UCYN-C,Cyanothecesp.). All diazotrophs tested, regardless their size and shape, were capable of forming aggregates andsunk, albeit at different velocities depending on the aggregation capacity. Overall, UCYN formed aggregates aslarge as those formed by thefilamentous diazotrophs (7000–32,014μm ESD, equivalent spherical diameter), andsunk at 100–400 m d1, i.e., at the same velocity asfilamentous diazotrophs (92–400 m d1). Although TEP aregenerally considered as enhancers of aggregation, TEP did not clearly influence aggregation rates nor sinkingvelocities during our study. We conclude that diazotrophs may be important contributors to carbon export inthe ocean and need to be considered in future studies to improve the accuracy of current regional and globalestimates of export.
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hal-04030404 , version 1 (16-03-2023)




Fatima-Ezzahra Ababou, Frédéric A. C. Le Moigne, Olivier Grosso, Catherine Guigue, Sandra Nunige, et al.. Mechanistic understanding of diazotroph aggregation and sinking: “A rolling tank approach”. Limnology and Oceanography, 2023, ⟨10.1002/lno.12301⟩. ⟨hal-04030404⟩
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