07 Jan 2022

07 Jan 2022

Review status: this preprint is currently under review for the journal BG.

Controlling factors on the global distribution of a representative marine heterotrophic diazotroph phylotype (Gamma A)

Zhibo Shao and Ya-Wei Luo Zhibo Shao and Ya-Wei Luo
  • State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, 361102 Xiamen, Fujian, China

Abstract. Heterotrophic diazotrophs emerge as a potentially important contributor to the global marine N2 fixation, while the factors controlling their distribution are unclear. Here, we explored what controls the distribution of the most sampled heterotrophic diazotroph phylotype, Gamma A, in the global ocean. First, we analyzed the relationship between nifH-based Gamma A abundance and climatological biological and environmental conditions. The carrying capacity of Gamma A abundance increased with net primary production (NPP) and saturated when NPP reached ~400 mg C m−2 d−1. The reduction in Gamma A abundance from its carrying capacity was mostly related to low temperature, which possibly slowed the decomposition of organic matter, and high concentration of dissolved iron, to which the explanation was elusive but could result from the competition with autotrophic diazotrophs. Using a generalized additive model, these climatological factors together explained 41 % of the variance in the Gamma A abundance. Second, in additional to the climatological background, we found that mesoscale cyclonic eddies can substantially elevate Gamma A abundance, implying that Gamma A can respond to short-term features and benefit from stimulated primary production by nutrient inputs. Overall, our results suggest that the distribution of Gamma A is most likely determined by the supply of organic matters, not by those factors controlling autotrophic diazotrophs, and therefore insight a niche differentiation between the heterotrophic and autotrophic N2 fixation. More samplings on Gamma A and other heterotrophic diazotroph phylotypes are needed to better reveal the controlling mechanisms of heterotrophic N2 fixation in the ocean.

Zhibo Shao and Ya-Wei Luo

Status: open (until 18 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-349', Anonymous Referee #1, 23 Jan 2022 reply

Zhibo Shao and Ya-Wei Luo

Data sets

Gamma A nifH abundance in the global ocean Zhibo Shao and Ya-wei Luo

Zhibo Shao and Ya-Wei Luo


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Short summary
Heterotrophic bacteria emerge as an important type of diazotrophs that fixing N2 in the ocean. We found that the most influential factor controlling the distribution of a representative marine heterotrophic diazotroph phylotype, Gamma A, is the sufficient supply of organic matters. Gamma A is also more abundant in low-iron regions. Our study suggests a niche differentiation of heterotrophic diazotrophs from autotrophic diazotrophs, as the latter prefers low-productive and high-iron oceans.