A neoproterozoic transition in the marine nitrogen cycle

TY - JOUR

T1 - A neoproterozoic transition in the marine nitrogen cycle

AU - Sánchez-Baracaldo, Patricia

AU - Ridgwell, Andy

AU - Raven, John A.

N1 - Copyright © 2014 Elsevier Ltd. All rights reserved.

PY - 2014/3/17

Y1 - 2014/3/17

N2 - The Neoproterozoic (1000-542 million years ago, Mya) was characterized by profound global environmental and evolutionary changes, not least of which included a major rise in atmospheric oxygen concentrations [1, 2], extreme climatic fluctuations and global-scale glaciation [3], and the emergence of metazoan life in the oceans [4, 5]. We present here phylogenomic (135 proteins and two ribosomal RNAs, SSU and LSU) and relaxed molecular clock (SSU, LSU, and rpoC1) analyses that identify this interval as a key transition in the marine nitrogen cycle. Specifically, we identify the Cryogenian (850-635 Mya) as heralding the first appearance of both marine planktonic unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing picocyanobacteria (Synechococcus and Prochlorococcus [6]). Our findings are consistent with the existence of open-ocean environmental conditions earlier in the Proterozoic adverse to nitrogen-fixers and their evolution-specifically, insufficient availability of molybdenum and vanadium, elements essential to the production of high-yielding nitrogenases. As these elements became more abundant during the Cryogenian [7, 8], both nitrogen-fixing cyanobacteria and planktonic picocyanobacteria diversified. The subsequent emergence of a strong biological pump in the ocean implied by our evolutionary reconstruction may help in explaining increased oxygenation of the Earth's surface at this time, as well as tendency for glaciation.

AB - The Neoproterozoic (1000-542 million years ago, Mya) was characterized by profound global environmental and evolutionary changes, not least of which included a major rise in atmospheric oxygen concentrations [1, 2], extreme climatic fluctuations and global-scale glaciation [3], and the emergence of metazoan life in the oceans [4, 5]. We present here phylogenomic (135 proteins and two ribosomal RNAs, SSU and LSU) and relaxed molecular clock (SSU, LSU, and rpoC1) analyses that identify this interval as a key transition in the marine nitrogen cycle. Specifically, we identify the Cryogenian (850-635 Mya) as heralding the first appearance of both marine planktonic unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing picocyanobacteria (Synechococcus and Prochlorococcus [6]). Our findings are consistent with the existence of open-ocean environmental conditions earlier in the Proterozoic adverse to nitrogen-fixers and their evolution-specifically, insufficient availability of molybdenum and vanadium, elements essential to the production of high-yielding nitrogenases. As these elements became more abundant during the Cryogenian [7, 8], both nitrogen-fixing cyanobacteria and planktonic picocyanobacteria diversified. The subsequent emergence of a strong biological pump in the ocean implied by our evolutionary reconstruction may help in explaining increased oxygenation of the Earth's surface at this time, as well as tendency for glaciation.

KW - Aquatic Organisms

KW - Biological Evolution

KW - Cyanobacteria

KW - Molybdenum

KW - Nitrogen Cycle

KW - Nitrogen Fixation

KW - Oceans and Seas

KW - Phylogeny

KW - Plankton

KW - Prochlorococcus

KW - Synechococcus

U2 - 10.1016/j.cub.2014.01.041

DO - 10.1016/j.cub.2014.01.041

M3 - Article

C2 - 24583016

SN - 0960-9822

VL - 24

SP - 652

EP - 657

JO - Current Biology

JF - Current Biology

IS - 6

ER -