Oceanographic and ecological consequences of iron localization in phytoplankton photosystems
Iron limits phytoplankton productivity and biomass in significant portions of the global ocean. A number of studies over the past decade have shown that iron's primary role in phytoplankton is as a cofactor in photosynthetic light processing and electron transport proteins, linking its availabi...
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ftcdlib:oai:escholarship.org/ark:/13030/qt9ng743pd 2023-05-15T16:02:36+02:00 Oceanographic and ecological consequences of iron localization in phytoplankton photosystems Hopkinson, Brian Matthew 2007-01-01 application/pdf https://escholarship.org/uc/item/9ng743pd unknown eScholarship, University of California qt9ng743pd https://escholarship.org/uc/item/9ng743pd public UCSD Oceanography. (Discipline) Dissertations Academic etd 2007 ftcdlib 2020-06-06T07:55:46Z Iron limits phytoplankton productivity and biomass in significant portions of the global ocean. A number of studies over the past decade have shown that iron's primary role in phytoplankton is as a cofactor in photosynthetic light processing and electron transport proteins, linking its availability directly to primary productivity. Multiple consequences of this localization were explored in this thesis. Because photosynthetic iron demands dominate phytoplankton iron requirements, it has been suggested that primary productivity may be co-limited by iron and light when the availability of both factors is reduced. Support for this hypothesis had been previously obtained in iron limited regions with deep mixed layers, but the possibility that iron-light co-limitation may occur outside areas conventionally thought to be iron limited was explored in Chapter II of this thesis. Phytoplankton, particularly larger diatoms, displayed responses indicative of iron-light co-limited at subsurface chlorophyll maxima in the Southern California Bight and the eastern tropical North Pacific. In these water columns, lack of iron availability limits the growth of larger organisms with consequences for carbon export efficiency and ecosystem structure. The distribution and speciation (redox and organic) of iron in one of these regions, the eastern tropical North Pacific, is discussed in Chapter IV. Photosynthetic physiology is strongly impacted by iron limitation, due to the high iron content of the photosynthetic apparatus. Assessment of variability in photosynthetic physiological states has proven useful as a diagnostic of iron stress in laboratory cultures and mesoscale iron addition experiments. In Chapter III, changes in photosynthetic physiology across a gradient in iron stress are examined in relation to experimental responses to iron addition. It was determined that in a region of natural iron fertilization in the southern Drake Passage, photosystem II characteristics were correlated with responses to iron addition, and could serve as good indicators of the degree of iron stress in a system. microbial ecosystems. The cycling of heme in the ocean is not well understood, but because it is hydrophobic and photosensitive, direct uptake by bacteria from particulates may be an important pathway of recycling. In Chapter V, the ability of a particle associated bacterium, Microscilla marina, to take up heme is discussed and a potential heme transport system is identified in its genome. The putative heme transport system is expressed and upregulated under iron stress and when growing on heme as an iron source. The genomes of many diverse marine bacteria were searched for similar uptake systems and genes with strong similarity to known heme transporters were identified in alpha- and gamma- proteobacteria. However, no putative heme transporters were identified in cyanobacteria or oligotrophic bacteria such as Pelagibacter ubique, suggesting heme is primarily available on particles or in rich environments, in agreement with its chemistry. Further investigations into the uptake capabilities of marine microorganisms may provide additional insights into trace metal cycling Other/Unknown Material Drake Passage University of California: eScholarship Drake Passage Pacific |
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University of California: eScholarship |
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UCSD Oceanography. (Discipline) Dissertations Academic |
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UCSD Oceanography. (Discipline) Dissertations Academic Hopkinson, Brian Matthew Oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
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UCSD Oceanography. (Discipline) Dissertations Academic |
description |
Iron limits phytoplankton productivity and biomass in significant portions of the global ocean. A number of studies over the past decade have shown that iron's primary role in phytoplankton is as a cofactor in photosynthetic light processing and electron transport proteins, linking its availability directly to primary productivity. Multiple consequences of this localization were explored in this thesis. Because photosynthetic iron demands dominate phytoplankton iron requirements, it has been suggested that primary productivity may be co-limited by iron and light when the availability of both factors is reduced. Support for this hypothesis had been previously obtained in iron limited regions with deep mixed layers, but the possibility that iron-light co-limitation may occur outside areas conventionally thought to be iron limited was explored in Chapter II of this thesis. Phytoplankton, particularly larger diatoms, displayed responses indicative of iron-light co-limited at subsurface chlorophyll maxima in the Southern California Bight and the eastern tropical North Pacific. In these water columns, lack of iron availability limits the growth of larger organisms with consequences for carbon export efficiency and ecosystem structure. The distribution and speciation (redox and organic) of iron in one of these regions, the eastern tropical North Pacific, is discussed in Chapter IV. Photosynthetic physiology is strongly impacted by iron limitation, due to the high iron content of the photosynthetic apparatus. Assessment of variability in photosynthetic physiological states has proven useful as a diagnostic of iron stress in laboratory cultures and mesoscale iron addition experiments. In Chapter III, changes in photosynthetic physiology across a gradient in iron stress are examined in relation to experimental responses to iron addition. It was determined that in a region of natural iron fertilization in the southern Drake Passage, photosystem II characteristics were correlated with responses to iron addition, and could serve as good indicators of the degree of iron stress in a system. microbial ecosystems. The cycling of heme in the ocean is not well understood, but because it is hydrophobic and photosensitive, direct uptake by bacteria from particulates may be an important pathway of recycling. In Chapter V, the ability of a particle associated bacterium, Microscilla marina, to take up heme is discussed and a potential heme transport system is identified in its genome. The putative heme transport system is expressed and upregulated under iron stress and when growing on heme as an iron source. The genomes of many diverse marine bacteria were searched for similar uptake systems and genes with strong similarity to known heme transporters were identified in alpha- and gamma- proteobacteria. However, no putative heme transporters were identified in cyanobacteria or oligotrophic bacteria such as Pelagibacter ubique, suggesting heme is primarily available on particles or in rich environments, in agreement with its chemistry. Further investigations into the uptake capabilities of marine microorganisms may provide additional insights into trace metal cycling |
format |
Other/Unknown Material |
author |
Hopkinson, Brian Matthew |
author_facet |
Hopkinson, Brian Matthew |
author_sort |
Hopkinson, Brian Matthew |
title |
Oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
title_short |
Oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
title_full |
Oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
title_fullStr |
Oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
title_full_unstemmed |
Oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
title_sort |
oceanographic and ecological consequences of iron localization in phytoplankton photosystems |
publisher |
eScholarship, University of California |
publishDate |
2007 |
url |
https://escholarship.org/uc/item/9ng743pd |
geographic |
Drake Passage Pacific |
geographic_facet |
Drake Passage Pacific |
genre |
Drake Passage |
genre_facet |
Drake Passage |
op_relation |
qt9ng743pd https://escholarship.org/uc/item/9ng743pd |
op_rights |
public |
_version_ |
1766398258310021120 |