The utilization of organic nutrients in marine phytoplankton with emphasis on coccolithophores [Elektronische Ressource] / vorgelegt von Ina Benner

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• Biologie

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• Publié par: universitat_bremen
• Publié le: 01 janvier 2008
• Nombre de lectures: 18
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

The utilization of organic nutrients
in marine phytoplankton
with emphasis on coccolithophores
Dissertation
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
- Dr. rer. nat. -
am Fachbereich 2 (Biologie/Chemie)
der Universit¨ at Bremen
vorgelegt von
Ina Benner
Bremen, 10.04.2008”Willst du dich am Ganzen erquicken,
so musst du das Ganze im Kleinen erblicken.”
Johann Wolfgang von GoetheCONTENTS i
Contents
0Preface 1
1 Introduction 3
1.1 Phytoplankton ................................. 3
1.2 Marine carbon cycle, sea surface temperature, and the impact of phyto-
plankton ..................................... 5
1.3 Nitrogenandphosphorusintheocean . ................... 7
1.4 Outline of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Studies 13
Study I: The Effects of Increased pCO and Temperature on the North Atlantic2
Spring Bloom: I. The Phytoplankton Community and Biogeochemical Re-
sponse ...................................... 15
Study II: Effects of inorganic and organic nitrogen and phosphorus additions on
a summer phytoplankton community in the North Atlantic . . . . . . . . . 35
Study III: Effects of urea on calcification of the coccolithophore Coccolithus
pelagicus(Haptophyceae) ........................... 53
Study IV: Species-specific utilization of organic nutrients . . . . . . . . . . . . . 65
Study V: The effect of nickel addition on coccolithophores growing on urea . . . 79
3 Discussion 85
3.1 Phytoplanktoncommunitycomposition . ................... 85
3.2 Nutrient limitation and calcification . . . . . . . . . . . . . . . . . . . . . . 87
3.3 Utilization of organic nutrients . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.4 Perspectives for future research . . . . . . . . . . . . . . . . . . . . . . . . 90
4 Summary 92
5 Zusammenfassung 94
6 References 97
7 Danksagung 119ii CONTENTSPREFACE 1
Preface
The anthropogenically caused increase of atmospheric carbon dioxide (CO )has many2
effects on the environmental conditions of the oceans. It changes seawater carbonate chem-
istry, sea surface temperature, stratification and mixing, light conditions, and nutrient
cycling (e.g. Maier-Reimer et al. 1996, Sarmiento et al. 1998, Rost & Riebesell 2004).
The environmental conditions and changes have repercussions for the biosphere, influ-
encing succession, distribution, and productivity of phytoplankton (e.g. Hutchinson 1961,
Gaedeke & Sommer 1986). In turn, phytoplankton activity can impact the climate by
driving many of the oceanic elemental cycles which are connected to the global cycles.
In view of the rapid changes in environmental conditions due to the increasing anthro-
pogenic CO emission, the investigation of the biological responses to climate change is2
the prerequisite to predict the future climate.
Coccolithophores are an important group of phytoplankton, because they influence the
oceanic carbon cycle in two ways: The organic carbon pump, influenced by photosynthe-
sis, causes a net draw down of CO from the atmosphere into the ocean and the carbonate2
counter pump, influenced by calcification, causes a net release of CO to the atmosphere.2
The flux of CO between the surface ocean and the atmosphere is mainly determined by2
the relative strength of the pumps (Rost & Riebesell 2004). A changed seawater carbon-
ate chemistry can decrease the calcification rate of coccolithophores (Riebesell et al. 2000,
Zondervan et al. 2001, Delille et al. 2005). Also the effects of the combination of some
climate-induced changes of environmental conditions were studied (e.g. Sciandra et al.
2003, Leonardos & Geider 2005, Hare et al. 2007, Feng et al. 2008), but mostly on species
level as opposed to phytoplankton community level. The investigations on a species level
help to understand processes like calcification, but the interactions of species are too com-
plex to predict the response of a phytoplankton community based on experiments on a
species level.
Increasing sea surface temperature will enhance stratification, which in turn may reduce
the input of inorganic nutrients into the surface layer, prevent organic nutrients from
mixing down at the same time, and reduce therewith the ratio of inorganic to organic
nutrients. This would favor species, which are able to utilize organic nutrients, but the
effects of a changed inorganic to organic nutrient ratio on a phytoplankton community are
unknown. The utilization of organic nutrients in general is known for some coccolitho-2 PREFACE
phore species (Ietswaart et al. 1994, Palenik & Henson 1997, Waser et al. 1998, Dyhrman
& Palenik 2003, Shaked et al. 2006), but only a fraction of the organic nutrients is biolog-
ically utilizable (Bronk 2002). Nothing is known about species-specific differences in the
utilization of the diverse compounds of the organic nutrients and little is known about
strain differences (Dyhrman & Palenik 2003). Knowledge about differences in the utiliza-
tion of organic nutrients could help to understand succession and distribution patterns
of coccolithophores. The ability to utilize organic nutrients is often dependent on trace
metals like zinc or nickel which are cofactors of enzymes processing organic nutrient com-
pounds. One study showed a possible Zn-P co-limitation in Emiliania huxleyi (Shaked
et al. 2006), but nothing is known about other species and other possible co-limitations.INTRODUCTION 3
1 Introduction
1.1 Phytoplankton
Phytoplankton are free-floating, unicellular algae, mostly too small to see with the naked
eye. This group of plants is taxonomically diverse and consists of at least 20,000 species
(Falkowski et al. 2003). Like all plants, phytoplankton is capable of photosynthesis and
forms the basis of the marine food web. One prokaryotic and eight eukaryotic major
phytoplankton taxa are known, but three phytoplankton clades (dinoflagellates, cocco-
lithophores, and diatoms) dominate the modern ocean (according to Falkowski et al.
2004). The prokaryotic cyanobacteria are suggested to be the majority of phytoplankton
in the Proterozoic history (∼1.5 billion years ago) before oxygenic photosynthesis spread
via endosymbiosis to eukaryotic clades. The eukaryotic photoautotrophs rived into two
lineages, the green algae (and land plants) and the red algae which includes the three
dominant phytoplankton clades dinoflagellates, coccolithophores, and diatoms. The dino-
flagellates and coccolithophores emerged in the Middle Triassic, whereas the diatoms
emerged later in the Mesozoic Era (for detailed information see the review of Falkowski
et al. 2004). The phytoplankton could be assigned to different ‘functional groups’ (accord-
ing to Falkowski et al. 2003). Functional groups are groups of organisms that are related
through common biogeochemical processes, independent from phylogenetic relationship.
These biogeochemical processes influence the cycling of elements in the ocean and between
the ocean and the atmosphere. Functional groups of phytoplankton include diazotrophs,
silicifiers, calcifiers and dimethylsulfide (DMS) producers. Diazothrophs (or N fixers)2
reduces N to ammonium-N (and then to organic molecules), silicifiers converts soluble2
silicic acid to solid hydrated amorphous opal, calcifiers converts dissolved inorganic carbon
and calcium to solid-phase calcite, and DMS producers synthesis dimethylsulfoniopropio-
nate (DMSP) which is enzymatically cleaved to DMS by bacteria and phytoplankton (for
further information see the review of Hood et al. 2006).
Different taxa of phytoplankton have different demands on the environmental condi-
tions. Nutrient availability, light level, and temperature are only some conditions which
decide competitive advantage and distribution of the different phytoplankton species (e.g.
Hutchinson 1961, Gaedeke & Sommer 1986). The continuously changing physical, chem-
ical, and biological factors of the ocean cause a continuous change of different species4 INTRODUCTION
and algae groups. This process of continuous community reorganization within one water
mass is termed succession (Smayda 1980). The seasonal succession of the three dominant
phytoplankton clades starts in general with a diatom spring bloom which is replaced by
a summer dinoflagellate or coccolithophore community (for detailed information about
succession see Smayda (1980)).
Diatoms contribute to the functional group of silicifiers, they build opal frustules (Martin-
J´ ez´equel et al. (2000)). Diatoms account for 40% of the total primary production in the
ocean and occur in all oceans, but mostly in sub-polar, and polar zones, coastal zones
and nutrient-rich upwelling regions (Sarthou et al. 2005 and references therein). Diatoms
often bloom in spring and appear to dominate as long as silicate concentrations are high
(Egge & Aksnes 1992, Egge & Heimdal 1994).
Coccolithophores contribute to the functional groups of calcifiers and of DMS produc-
ers. The majority of coccolithophore species occurs in the warmer regions (Lalli &
Parsons 1994b), although some species thrive in colder regions (e.g. Emiliania huxleyi
and Coccolithus pelagicus) (Winter et al. 1994). E. huxleyi is the best studied coccolitho-
phore due to the easy culturing of this species, the easy observation of blooms by remote
sensing techniques (Brown & Yode