Crocosphaera as a major consumer of fixed nitrogen despite its capability of nitrogen fixation

Masuda, T.; Inomura, K.; Kodama, T.; Shiozaki, T.; Kitajima, S.; Armin, G.; Matsui, T.; Suzuki, K.; Takeda, S.; Prasil, O.; Furuya, K.

doi:10.1101/2021.07.28.454264

bioRxiv · 10.1101/2021.07.28.454264

Crocosphaera as a major consumer of fixed nitrogen despite its capability of nitrogen fixation

Masuda, T.·Inomura, K.·Kodama, T.·Shiozaki, T.·Kitajima, S.·Armin, G.·Matsui, T.·Suzuki, K.·Takeda, S.·Prasil, O.·Furuya, K.

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Abstract

Crocosphaera watsonii (hereafter Crocosphaera) is a key nitrogen (N) fixer in the ocean, but its ability to consume combined N sources is still unclear. Using in situ microcosm incubations with an ecological model, we show that Crocosphaera has high competitive capability both under low and moderately high combined N concentrations. In field incubations, Crocosphaera accounted for the highest consumption of ammonium and nitrate, followed by pico-eukaryotes. The model analysis shows that cells have a high ammonium uptake rate ([~]7 mol N (mol N)-1 d-1 at the maximum), which allows them to compete against pico-eukaryotes and non-diazotrophic cyanobacteria when combined N is sufficiently available. Even when combined N is depleted, their capability of nitrogen fixation allows higher growth rates compared to potential competitors. These results suggest the high fitness of Crocosphaera in combined N limiting, oligotrophic oceans, and thus heightens its potential significance in its ecosystem and in biogeochemical cycling.

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Masuda, T., Inomura, K., Kodama, T., Shiozaki, T., Kitajima, S., Armin, G., Matsui, T., Suzuki, K., Takeda, S., Prasil, O., Furuya, K.. 2021-07-30. Crocosphaera as a major consumer of fixed nitrogen despite its capability of nitrogen fixation. https://doi.org/10.1101/2021.07.28.454264

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