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Nitrifier adaptation to low energy flux controls inventory of reduced nitrogen in the dark ocean.

Abstract：

:Ammonia oxidation to nitrite and its subsequent oxidation to nitrate provides energy to the two populations of nitrifying chemoautotrophs in the energy-starved dark ocean, driving a coupling between reduced inorganic nitrogen (N) pools and production of new organic carbon (C) in the dark ocean. However, the relationship between the flux of new C production and the fluxes of N of the two steps of oxidation remains unclear. Here, we show that, despite orders-of-magnitude difference in cell abundances between ammonia oxidizers and nitrite oxidizers, the two populations sustain similar bulk N-oxidation rates throughout the deep waters with similarly high affinities for ammonia and nitrite under increasing substrate limitation, thus maintaining overall homeostasis in the oceanic nitrification pathway. Our observations confirm the theoretical predictions of a redox-informed ecosystem model. Using balances from this model, we suggest that consistently low ammonia and nitrite concentrations are maintained when the two populations have similarly high substrate affinities and their loss rates are proportional to their maximum growth rates. The stoichiometric relations between the fluxes of C and N indicate a threefold to fourfold higher C-fixation efficiency per mole of N oxidized by ammonia oxidizers compared to nitrite oxidizers due to nearly identical apparent energetic requirements for C fixation of the two populations. We estimate that the rate of chemoautotrophic C fixation amounts to ∼1 × 1013 to ∼2 × 1013 mol of C per year globally through the flux of ∼1 × 1014 to ∼2 × 1014 mol of N per year of the two steps of oxidation throughout the dark ocean.

journal_name

Proc Natl Acad Sci U S A

journal_title

Proceedings of the National Academy of Sciences of the United States of America

authors

Zhang Y,Qin W,Hou L,Zakem EJ,Wan X,Zhao Z,Liu L,Hunt KA,Jiao N,Kao SJ,Tang K,Xie X,Shen J,Li Y,Chen M,Dai X,Liu C,Deng W,Dai M,Ingalls AE,Stahl DA,Herndl GJ

doi

10.1073/pnas.1912367117

subject

Has Abstract

pub_date

2020-03-03 00:00:00

pages

4823-4830

issue

eissn

0027-8424

issn

1091-6490

pii

1912367117

journal_volume

117

pub_type

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Nitrifier adaptation to low energy flux controls inventory of reduced nitrogen in the dark ocean.