TY - JOUR
T1 - Do phytoplankton require oxygen to survive?
T2 - A hypothesis and model synthesis from oxygen minimum zones
AU - Wong, Jane C.Y.
AU - Raven, John A.
AU - Aldunate, Montserrat
AU - Silva, Sebastián
AU - Gaitán-Espitia, Juan Diego
AU - Vargas, Cristian A.
AU - Ulloa, Osvaldo
AU - von Dassow, Peter
N1 - Funding Information:
We thank the chief scientists, captains, crews, and scientific support personnel of R/V Cabo de Hornos, R/V Nathaniel B. Palmer, R/V Robert Brown, and R/V New Horizon. We also thank Gadiel Alarcón and Cristian Venegas for assistance in sample collection. This work was supported by grants from the National Agency for Research and Development (ANID) of Chile (Grants ICN12_019‐IMO and Fondecyt 1161483) and the Instituto Milenio de Oceanografía (Grant 120019). The University of Dundee is a Scottish Registered Charity, No SC015096.
Publisher Copyright:
© 2023 Association for the Sciences of Limnology and Oceanography.
PY - 2023/7
Y1 - 2023/7
N2 - It is commonly known that phytoplankton have a pivotal role in marine biogeochemistry and ecosystems as carbon fixers and oxygen producers, but their response to deoxygenation has scarcely been studied. Nonetheless, in the major oceanic oxygen minimum zones (OMZs), all surface phytoplankton groups, regardless of size, disappear and are replaced by unique cyanobacteria lineages below the oxycline. To develop reasonable hypotheses to explain this pattern, we conduct a review of available information on OMZ phytoplankton, and we re-analyze previously published data (flow cytometric and hydrographic) on vertical structure of phytoplankton communities in relation to light and O2 levels. We also review the physical constraints on O2 acquisition as well as O2-dependent metabolisms in phototrophs. These considerations, along with estimates of the photosynthetic capacity of phytoplankton along OMZ depth profiles using published data, suggest that top-down grazing, respiratory demand, and irradiance are insufficient to fully explain the vertical structure observed in the upper, more sunlit portions of OMZs. Photorespiration and water–water cycles are O2-dependent pathways with low O2 affinities. Although their metabolic roles are still poorly understood, a hypothetical dependence on such pathways by the phytoplankton adapted to the oxic ocean might explain vertical patterns in OMZs and results of laboratory experiments. This can be represented in a simple model in which the requirement for photorespiration in surface phytoplankton and O2-inhibition of OMZ lineages reproduces the observed vertical fluorescence profiles and the replacement of phytoplankton adapted to O2 by lineages restricted to the most O2-deficient waters. A high O2 requirement by modern phytoplankton would suggest a positive feedback that intensifies trends in OMZ extent and ocean oxygenation or deoxygenation, both in Earth's past and in response to current climate change.
AB - It is commonly known that phytoplankton have a pivotal role in marine biogeochemistry and ecosystems as carbon fixers and oxygen producers, but their response to deoxygenation has scarcely been studied. Nonetheless, in the major oceanic oxygen minimum zones (OMZs), all surface phytoplankton groups, regardless of size, disappear and are replaced by unique cyanobacteria lineages below the oxycline. To develop reasonable hypotheses to explain this pattern, we conduct a review of available information on OMZ phytoplankton, and we re-analyze previously published data (flow cytometric and hydrographic) on vertical structure of phytoplankton communities in relation to light and O2 levels. We also review the physical constraints on O2 acquisition as well as O2-dependent metabolisms in phototrophs. These considerations, along with estimates of the photosynthetic capacity of phytoplankton along OMZ depth profiles using published data, suggest that top-down grazing, respiratory demand, and irradiance are insufficient to fully explain the vertical structure observed in the upper, more sunlit portions of OMZs. Photorespiration and water–water cycles are O2-dependent pathways with low O2 affinities. Although their metabolic roles are still poorly understood, a hypothetical dependence on such pathways by the phytoplankton adapted to the oxic ocean might explain vertical patterns in OMZs and results of laboratory experiments. This can be represented in a simple model in which the requirement for photorespiration in surface phytoplankton and O2-inhibition of OMZ lineages reproduces the observed vertical fluorescence profiles and the replacement of phytoplankton adapted to O2 by lineages restricted to the most O2-deficient waters. A high O2 requirement by modern phytoplankton would suggest a positive feedback that intensifies trends in OMZ extent and ocean oxygenation or deoxygenation, both in Earth's past and in response to current climate change.
UR - http://www.scopus.com/inward/record.url?scp=85158122175&partnerID=8YFLogxK
U2 - 10.1002/lno.12367
DO - 10.1002/lno.12367
M3 - Review article
AN - SCOPUS:85158122175
SN - 0024-3590
VL - 68
SP - 1417
EP - 1437
JO - Limnology and Oceanography
JF - Limnology and Oceanography
IS - 7
ER -